common/colorchecker.c

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/*
    This file is part of darktable,
    Copyright (C) 2025-2026 Guillaume Stutin.
 
    darktable is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
 
    darktable is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License
    along with darktable.  If not, see <http://www.gnu.org/licenses/>.
*/
 
#include "colorchecker.h"
#include "common/colorspaces_inline_conversions.h"
#include "darktable.h"
#include "file_location.h"
 
#include <glib.h>
#include <inttypes.h>
#include <lcms2.h>
 
// In some environments ERROR is already defined, ie: WIN32
#if defined(ERROR)
#undef ERROR
#endif // defined (ERROR)
 
#define ERROR           \
  {                     \
    lineno = __LINE__;  \
    goto error;         \
  }
  
typedef enum parser_state_t {
  BLOCK_NONE = 0,
  BLOCK_BOXES,
  BLOCK_BOX_SHRINK,
  BLOCK_REF_ROTATION,
  BLOCK_XLIST,
  BLOCK_YLIST,
  BLOCK_EXPECTED
} parser_state_t;
 
typedef struct cht_box_t {
  char key_letter; // 'D', 'X', or 'Y'
  char *label_x_start;
  char *label_x_end;
  char *label_y_start;
  char *label_y_end;
  float width;
  float height;
  float x_origin;
  float y_origin;
  float x_increment;
  float y_increment;
} cht_box_t;
 
typedef struct cht_box_F_t {
  float ax; // top left corner
  float ay; // top left corner
  float bx; // top right corner
  float by; // top right corner
  float cx; // bottom left corner
  float cy; // bottom left corner
  float dx; // bottom right corner
  float dy; // bottom right corner
  float width; // width of the frame
  float height; // height of the frame
} cht_box_F_t;
 
#define TWO_SQRT2f 2.8284271247461900976f // sqrt(2) * 2
 
static void _dt_colorchecker_copy_patch(dt_color_checker_patch *dest, const dt_color_checker_patch *src)
{
  if(IS_NULL_PTR(dest) || IS_NULL_PTR(src)) return;
 
  dest->name = g_strdup(src->name);
  dest->x = src->x;
  dest->y = src->y;
  dest->Lab[0] = src->Lab[0];
  dest->Lab[1] = src->Lab[1];
  dest->Lab[2] = src->Lab[2];
}
 
void dt_colorchecker_copy(dt_color_checker_t *dest, const dt_color_checker_t *src)
{
  if(IS_NULL_PTR(dest) || IS_NULL_PTR(src)) return;
 
  dest->name = g_strdup(src->name);
  dest->author = g_strdup(src->author);
  dest->date = g_strdup(src->date);
  dest->manufacturer = g_strdup(src->manufacturer);
  dest->type = src->type;
  dest->radius = src->radius;
  dest->ratio = src->ratio;
  dest->patches = src->patches;
  dest->size[0] = src->size[0];
  dest->size[1] = src->size[1];
  dest->middle_grey = src->middle_grey;
  dest->white = src->white;
  dest->black = src->black;
 
  if(!IS_NULL_PTR(src->values))
  {
    dest->values = dt_colorchecker_patch_array_init(src->patches);
    if(IS_NULL_PTR(dest->values))
    {
      fprintf(stderr, "Error: Memory allocation failed for color checker values.\n");
      return;
    }
 
    for(int i = 0; i < src->patches; i++)
    {
      _dt_colorchecker_copy_patch(&dest->values[i], &src->values[i]);
    }
  }
  else
  {
    dest->values = NULL;
  }
  dest->finished = TRUE;
}
 
static cht_box_F_t *_dt_cht_extract_F(const char **tokens)
{
  cht_box_F_t *frame_coordinates = (cht_box_F_t *)malloc(sizeof(cht_box_F_t));
  if(IS_NULL_PTR(frame_coordinates)) return NULL;
 
  size_t index = 0;
  float extracted_coords[8] = { 0.f };
  for(size_t i = 0; tokens[i] != NULL; i++)
  {
    if(index >= 8) break; // Prevent overflow
 
    if(g_ascii_isdigit(tokens[i][0])) // note : always positive numbers
    {
      extracted_coords[index] = (float)g_ascii_strtod(tokens[i], NULL);
      index++;
    }
  }
 
  // copy the extracted coordinates to the frame_coordinates structure
  frame_coordinates->ax = extracted_coords[0];
  frame_coordinates->ay = extracted_coords[1];
  frame_coordinates->bx = extracted_coords[2];
  frame_coordinates->by = extracted_coords[3];
  frame_coordinates->cx = extracted_coords[4];
  frame_coordinates->cy = extracted_coords[5];
  frame_coordinates->dx = extracted_coords[6];
  frame_coordinates->dy = extracted_coords[7];
 
  // Compute the width and height of the frame
  frame_coordinates->width = extracted_coords[2] - extracted_coords[0];
  frame_coordinates->height = extracted_coords[5] - extracted_coords[1];
 
  return frame_coordinates;
}
 
static dt_colorchecker_chart_spec_t *_dt_colorchecker_chart_spec_init()
{
  dt_colorchecker_chart_spec_t *result = (dt_colorchecker_chart_spec_t *)malloc(sizeof(dt_colorchecker_chart_spec_t));
  if(IS_NULL_PTR(result)) return NULL;
 
  result->type = NULL;
  result->radius = 0.f;
  result->ratio = 0.f;
  result->size[0] = 0;
  result->size[1] = 0;
  result->middle_grey = 0;
  result->white = 0;
  result->black = 0;
  result->num_patches = 0;
  result->colums = 0;
  result->rows = 0;
  result->patch_width = FLT_MAX;
  result->patch_height = FLT_MAX;
  result->patch_offset_x = 0.f;
  result->patch_offset_y = 0.f;
  result->guide_size[0] = 0.f;
  result->guide_size[1] = 0.f;
  result->patches = NULL;
 
  return result;
}
 
static void _dt_colorchecker_chart_spec_cleanup(dt_colorchecker_chart_spec_t *chart_spec)
{
  if(IS_NULL_PTR(chart_spec)) return;
 
  dt_free(chart_spec->type);
 
  // Free the patches' gslist
  if(chart_spec->patches)
    g_slist_free_full(chart_spec->patches, dt_colorchecker_patch_cleanup_list);
 
  dt_free(chart_spec);
}
 
static dt_color_checker_patch *_dt_colorchecker_patch_init()
{
  dt_color_checker_patch *patch = (dt_color_checker_patch *)malloc(sizeof(dt_color_checker_patch));
  if(IS_NULL_PTR(patch)) return NULL;
 
  patch->name = NULL;
  patch->Lab[0] = 0.f;
  patch->Lab[1] = 0.f;
  patch->Lab[2] = 0.f;
  patch->x = -1.f;
  patch->y = -1.f;
 
  return patch;
}
 
static void _dt_cht_box_cleanup(void *data)
{
  cht_box_t *box = (cht_box_t *)data;
  if(IS_NULL_PTR(box)) return;
 
  dt_free(box->label_x_start);
  dt_free(box->label_x_end);
  dt_free(box->label_y_start);
  dt_free(box->label_y_end);
  dt_free(box);
}
 
static cht_box_t *_dt_cht_box_extract(const char **tokens)
{
  cht_box_t *box = (cht_box_t *)calloc(1, sizeof(cht_box_t));
  if(IS_NULL_PTR(box)) return NULL;
 
  size_t index = 0;
  size_t i = 0;
  while(!IS_NULL_PTR(tokens[i]) && index <= 10)
  {
    if(tokens[i][0] != '\0')
    {
      float value = 0;
      const char *string = tokens[i];
 
      // Check if the token is a digit or a negative number before converting the string to float
      if(g_ascii_isdigit(tokens[i][0]) || (tokens[i][0] == '-' && g_ascii_isdigit(tokens[i][1])))
        value = (float)g_ascii_strtod(tokens[i], NULL);
 
      switch(index)
      {
        case 0: box->key_letter    = tokens[i][0]; index++; break; // 'D', 'X', or 'Y'
        case 1: box->label_x_start = g_strdup(string); index++; break;
        case 2: box->label_x_end   = g_strdup(string); index++; break;
        case 3: box->label_y_start = g_strdup(string); index++; break;
        case 4: box->label_y_end   = g_strdup(string); index++; break;
        case 5: box->width         = value; index++; break;
        case 6: box->height        = value; index++; break;
        case 7: box->x_origin      = value; index++; break;
        case 8: box->y_origin      = value; index++; break;
        case 9: box->x_increment   = value; index++; break;
        case 10: box->y_increment  = value; index++; break;
        default: fprintf(stderr, "Unexpected token in cht box extraction: %s\n", tokens[i]);
                 _dt_cht_box_cleanup(box);
                 return NULL;
      }
    }
    i++;
  }
 
  return box;
}
 
static char *_increment_string(const gchar *in)
{
  if (IS_NULL_PTR(in) || *in == '\0') return NULL;
 
  gchar *result = g_strdup(in);
  if(IS_NULL_PTR(result)) return NULL;
 
  size_t len = strlen(result);
 
  if(len == 0)
  {
    dt_free(result);
    return NULL;
  }
 
  for(int i = (int)len - 1; i >= 0; i--)
  {
    // for numbers
    if(g_ascii_isdigit(result[i]))
    {
      if(result[i] == '9')
      {
        result[i] = '0';
        continue;
      }
      result[i]++;
      break;
    }
    // for letters
    else if(g_ascii_isalpha(result[i]))
    {
      if(result[i] == 'z' || result[i] == 'Z')
      {
        result[i] = (result[i] == 'z') ? 'a' : 'A';
        continue;
      }
      result[i]++;
      break;
    }
    // there should not be other cases
    else
    {
      break;
    }
  }
 
  return result;
}
 
static inline const char *_remove_leading_zeros(const char *in)
{
  if(IS_NULL_PTR(in) || *in == '\0') return "";
  const char *start = in;
  while(*start == '0') start++;
 
  return start;
}
 
static gboolean _dt_cht_generate_patch_list(dt_colorchecker_chart_spec_t *chart, const cht_box_t *cht_patch, const cht_box_F_t *F_box)
{
  gboolean result = FALSE;
  int lineno = 0;
 
  gchar *current_colum = NULL;
  gchar *current_row = NULL;
  gchar *last_label = NULL;
  GSList *patch_tail = NULL;
 
  // Input validation
  if(IS_NULL_PTR(cht_patch))
  {
    fprintf(stderr, "Invalid cht_patch");
    ERROR;
  }
 
  if(IS_NULL_PTR(chart))
  {
    fprintf(stderr, "Invalid chart");
    ERROR;
  }
 
  // The key letter determines the axes to begin to iterate
  gboolean swap_axes = (cht_patch->key_letter == 'Y') ? TRUE : FALSE;
 
  // Unpack strings from cht_patch
  const char *start_colum = swap_axes ? cht_patch->label_y_start : cht_patch->label_x_start;
  const char *end_colum = swap_axes ? cht_patch->label_y_end : cht_patch->label_x_end;
 
  const char *start_row = swap_axes ? cht_patch->label_x_start : cht_patch->label_y_start;
  const char *end_row = swap_axes ? cht_patch->label_x_end : cht_patch->label_y_end;
 
  // start shouldn't be greater than end
  if(g_strcmp0(start_colum, end_colum) > 0 || g_strcmp0(start_row, end_row) > 0)
    ERROR
 
  // we want the center of the patch.
  const float patch_w = cht_patch->width / 2;
  const float patch_h = cht_patch->height / 2;
 
  // Prepare the initial x and y coordinates
  float origin_x = cht_patch->x_origin - (chart->guide_size[0] / 2) + patch_w - F_box->ax;
  float origin_y = cht_patch->y_origin - (chart->guide_size[1] / 2) + patch_h - F_box->ay;
 
  // build the last label name, for comparison
  const char *last_label_colum = (end_colum[0] != '_') ? _remove_leading_zeros(end_colum) : NULL;
  const char *last_label_row = (end_row[0] != '_') ? _remove_leading_zeros(end_row) : NULL;
  last_label = g_strconcat(last_label_colum ? last_label_colum : "", last_label_row ? last_label_row : "", NULL);
  if(IS_NULL_PTR(last_label)) ERROR
 
  // Copy string for manipulation
  current_colum = g_strdup(start_colum);
  if(IS_NULL_PTR(current_colum)) ERROR
  const char *colum_last = swap_axes ? cht_patch->label_y_end : cht_patch->label_x_end;
  const char *row_last = swap_axes ? cht_patch->label_x_end : cht_patch->label_y_end;
  const float inv_frame_width = 1.f / (F_box->width - chart->guide_size[0]);
  const float inv_frame_height = 1.f / (F_box->height - chart->guide_size[1]);
 
  patch_tail = g_slist_last(chart->patches);
 
  // Iterate over chart columns and rows, creating one patch per label until the CHT end label is reached.
  int index_colum = 0;
  while(g_strcmp0(current_colum, colum_last) <= 0)
  {
    current_row = g_strdup(start_row);
    if(IS_NULL_PTR(current_row)) ERROR
    int index_row = 0;
 
    while(g_strcmp0(current_row, row_last) <= 0)
    {
      // Create the label
      const char *label_colum = current_colum[0] != '_' ? _remove_leading_zeros(current_colum) : NULL;
      const char *label_row = current_row[0] != '_' ? _remove_leading_zeros(current_row) : NULL;
 
      gchar *label = g_strconcat(label_colum ? label_colum : "", label_row ? label_row : "", NULL);
      if(IS_NULL_PTR(label)) ERROR
 
      // Create the patch
      dt_color_checker_patch *patch = _dt_colorchecker_patch_init();
      if(IS_NULL_PTR(patch))
      {
        dt_free(label);
        ERROR
      }
 
      // Set the patch properties
      patch->name = label;
      label = NULL;
 
      int index_x = swap_axes ? index_row : index_colum;
      float temp_x = (origin_x + (cht_patch->x_increment * index_x)) * inv_frame_width;
 
      int index_y = swap_axes ? index_colum : index_row;
      float temp_y = (origin_y + (cht_patch->y_increment * index_y)) * inv_frame_height;
 
      patch->x = temp_x;
      patch->y = temp_y;
 
      // Add the node explicitly at the current tail: g_slist_append() would rescan
      // the whole list for every patch and turn large charts into quadratic work.
      GSList *patch_node = g_slist_alloc();
      patch_node->data = patch;
      patch_node->next = NULL;
      if(!IS_NULL_PTR(patch_tail))
        patch_tail->next = patch_node;
      else
        chart->patches = patch_node;
      patch_tail = patch_node;
 
      const gboolean last_patch_reached = !g_strcmp0(patch->name, last_label);
      if(last_patch_reached) goto out;
      if(!g_strcmp0(current_row, "_")) break;
 
      // increment x in a new string and pass the ownership to current_row
      gchar *temp = _increment_string(current_row);
      dt_free(current_row)
      current_row = temp;
 
      chart->colums = MAX(chart->colums, index_row + 1);
      index_row++;
    }
 
    dt_free(current_row)
    current_row = NULL;
 
    // increment y in a new string and pass the ownership to current_colum
    gchar *temp = _increment_string(current_colum);
    dt_free(current_colum)
    current_colum = temp;
 
    chart->rows = MAX(chart->rows, index_colum + 1);
    index_colum++;
  }
 
out:
  result = TRUE;
  goto end;
 
error:
  fprintf(stderr, "error parsing CHT file, in %s %s:%d\n", __FUNCTION__, __FILE__, lineno);
 
end:
  dt_free(last_label)
  dt_free(current_row)
  dt_free(current_colum)
  return result;
}
 
static GList *_parse_cht(const char *filename)
{
  GList *result = NULL;
 
  if(IS_NULL_PTR(filename))
  {
    fprintf(stderr, "Invalid filename for CHT parsing");
    return NULL;
  }
 
  int lineno = 0;
  GIOChannel *fp = g_io_channel_new_file(filename, "r", NULL);
  if(IS_NULL_PTR(fp))
  {
    fprintf(stderr, "Error opening '%s'\n", filename);
    return NULL;
  }
 
  // parser control
  GString *line = g_string_new(NULL);
  parser_state_t last_block = BLOCK_NONE;
  int skip_block = 0;
 
  // main loop over the input file
  while(g_io_channel_read_line_string(fp, line, NULL, NULL) == G_IO_STATUS_NORMAL)
  {
    if(line->len == 0)
    {
      skip_block = 0;
      continue;
    }
    if(skip_block) continue;
 
    // we should be at the start of a block now
    const char *c = line->str;
    if(IS_NULL_PTR(c)) continue;
 
    while(*c == ' ') c++; // skip leading spaces
    gchar **line_tokens = g_strsplit(c, " ", 0);
 
    if(!IS_NULL_PTR(line_tokens[0]) && !g_strcmp0(line_tokens[0], "BOXES") && last_block < BLOCK_BOXES)
    {
      last_block = BLOCK_BOXES;
 
      // let's have another loop reading from the file.
      while(g_io_channel_read_line_string(fp, line, NULL, NULL) == G_IO_STATUS_NORMAL)
      {
        if(line->len == 0) break;
 
        c = line->str;
        while(*c == ' ') c++; // skip leading spaces
 
        gchar **box_tokens = g_strsplit(c, " ", 0);
        if(!IS_NULL_PTR(box_tokens[0])
            && (!g_strcmp0(box_tokens[0], "F")
                || !g_strcmp0(box_tokens[0], "D")
                || !g_strcmp0(box_tokens[0], "X")
                || !g_strcmp0(box_tokens[0], "Y")))
        {
          result = g_list_append(result, box_tokens);
        }
        else
        {
          g_strfreev(box_tokens);
        }
      }
    }
 
    if(!IS_NULL_PTR(line_tokens[0]) && !g_strcmp0(line_tokens[0], "BOX_SHRINK") && last_block < BLOCK_BOX_SHRINK)
    {
      last_block = BLOCK_BOX_SHRINK;
      skip_block = 1;
    }
 
    g_strfreev(line_tokens);
  }
 
  if(last_block == BLOCK_NONE)
    ERROR
 
  goto end;
 
error:
  fprintf(stderr, "error parsing CHT file, in %s %s:%d\n", __FUNCTION__, __FILE__, lineno);
 
end:
  if(line) g_string_free(line, TRUE);
  if(fp) g_io_channel_unref(fp);
  return result;
}
 
// according to cht_format.html from argyll:
// "The keywords and associated data must be used in the following order: BOXES, BOX_SHRINK, REF_ROTATION,
// XLIST, YLIST and EXPECTED."
static gboolean _dispatch_cht_data(GList **boxes, dt_colorchecker_chart_spec_t *chart_spec)
{
  gboolean result = FALSE;
  int lineno = 0;
 
  // data gathered from the CHT file
  cht_box_F_t *F_box = NULL;
  GList *boxes_list = NULL;
 
  float chart_radius = -1.f;
 
  if(IS_NULL_PTR(boxes) || IS_NULL_PTR(chart_spec))
  {
    fprintf(stderr, "Invalid input to dispatch cht data");
    ERROR
  }
 
  // Gather the frame box and every patch-row/column box before deriving the chart geometry.
  for(GList *lines = *boxes; lines; lines = g_list_next(lines))
  {
    const char **tokens = (const char **)lines->data;
    if(IS_NULL_PTR(tokens)) ERROR
 
    const char letter = tokens[0][0];
    if(letter == 'F')
    {
      F_box = _dt_cht_extract_F(tokens);
    }
 
    else if(letter == 'D' || letter == 'X' || letter == 'Y')
    {
      cht_box_t *box = _dt_cht_box_extract(tokens);
      if(IS_NULL_PTR(box)) ERROR
 
      boxes_list = g_list_append(boxes_list, box);
    }
  }
 
  if(IS_NULL_PTR(F_box)) ERROR
 
  // Fill the colorchecker spec structure
  chart_spec->ratio = F_box->height / F_box->width;
  chart_radius = hypotf(F_box->height, F_box->width);
 
  for(GList *iter = boxes_list; iter; iter = g_list_next(iter))
  {
    cht_box_t *box = (cht_box_t *)iter->data;
    if(IS_NULL_PTR(box)) ERROR
 
    if(box->key_letter == 'D')
    {
      // Save the guide corner sizes when they are specified, to changes the patches area size in consequence.
      if(!g_strcmp0(box->label_x_start,"MARK")) chart_spec->guide_size[0] = box->width - box->x_origin;
      if(!g_strcmp0(box->label_x_start,"MARK")) chart_spec->guide_size[1] = box->height - box->y_origin;
    }
 
    else if(box->key_letter == 'X' || box->key_letter == 'Y')
    {
      chart_spec->patch_width  = MIN(chart_spec->patch_width, box->width);
      chart_spec->patch_height = MIN(chart_spec->patch_height, box->height);
 
      if(!_dt_cht_generate_patch_list(chart_spec, box, F_box))
      {
        ERROR
      }
    }
  }
 
  chart_spec->num_patches = g_slist_length(chart_spec->patches);
  chart_spec->size[0] = (size_t)chart_spec->colums;
  chart_spec->size[1] = (size_t)chart_spec->rows;
  const float patch_radius = hypotf(chart_spec->patch_width, chart_spec->patch_height) / TWO_SQRT2f;
  chart_spec->radius = patch_radius / chart_radius;
 
  result = TRUE;
  goto end;
 
error:
  fprintf(stderr, "Error dispatching CHT file, in %s %s:%d\n", __FUNCTION__, __FILE__, lineno);
 
end:
  dt_free(F_box);
  if(!IS_NULL_PTR(boxes_list)) g_list_free_full(boxes_list, _dt_cht_box_cleanup);
 
  return result;
}
 
static gboolean _dt_colorchecker_open_cht(const char *filename, dt_colorchecker_chart_spec_t *chart_spec)
{
  if(IS_NULL_PTR(filename) || IS_NULL_PTR(chart_spec))
  {
    fprintf(stderr, "[_dt_colorchecker_open_cht] Error: Invalid input parameters.\n");
    return FALSE;
  }
 
  GList *boxes = _parse_cht(filename);
  if(IS_NULL_PTR(boxes))
  {
    fprintf(stderr, "[_dt_colorchecker_open_cht] Error parsing CHT file '%s'\n", filename);
    return FALSE;
  }
 
  if(!_dispatch_cht_data(&boxes, chart_spec))
  {
    fprintf(stderr, "[_dt_colorchecker_open_cht] Error dispatching CHT data from '%s'\n", filename);
    g_list_free_full(boxes, (GDestroyNotify)g_strfreev);
    return FALSE;
  }
 
  chart_spec->type = g_path_get_basename(filename);
 
  g_list_free_full(boxes, (GDestroyNotify)g_strfreev);
 
  return TRUE;
}
 
static inline dt_colorchecker_CGATS_types _dt_CGATS_get_type_value(const char *type);
 
static inline dt_colorchecker_material_types _dt_colorchecker_IT8_get_material_type(const cmsHANDLE *hIT8)
{
  if(IS_NULL_PTR(*hIT8))
  {
    fprintf(stderr, "[_dt_colorchecker_IT8_get_material_type] Error: Invalid IT8 handle provided.\n");
    return COLOR_CHECKER_MATERIAL_UNKNOWN;
  }
 
  const int CGATS_type_value = _dt_CGATS_get_type_value(cmsIT8GetSheetType(*hIT8));
  switch(CGATS_type_value)
  {
    case CGATS_TYPE_IT8_7_1:
      return COLOR_CHECKER_MATERIAL_TRANSPARENT;
 
    case CGATS_TYPE_IT8_7_2:
    case CGATS_TYPE_CTI3:
      return COLOR_CHECKER_MATERIAL_OPAQUE;
 
    case CGATS_TYPE_UNKOWN:
    default:
      return COLOR_CHECKER_MATERIAL_UNKNOWN;
  }
 
  return COLOR_CHECKER_MATERIAL_UNKNOWN;
}
 
 
static inline const char *_dt_colorchecker_get_material_string(const dt_colorchecker_material_types material)
{
  if(material >= COLOR_CHECKER_MATERIAL_TRANSPARENT && material < COLOR_CHECKER_MATERIAL_UNKNOWN)
    return colorchecker_material_types[material];
 
  // else
  fprintf(stderr, "[_dt_colorchecker_get_material_string] Error: Unknown material type.\n");
  return NULL;
}
 
static inline dt_colorchecker_CGATS_types _dt_CGATS_get_type_value(const char *type)
{
  if(IS_NULL_PTR(type)) return CGATS_TYPE_UNKOWN;
 
  // Scan only supported names and return the sentinel for unsupported metadata.
  for(dt_colorchecker_CGATS_types t = CGATS_TYPE_IT8_7_1; t < CGATS_TYPE_UNKOWN; t++)
  {
    if(!g_strcmp0(type, CGATS_types[t])) return t;
  }
 
  return CGATS_TYPE_UNKOWN;
}
 
static gchar *_dt_colorchecker_get_standard_type(const char *type)
{
  gchar *result = NULL;
 
  if(IS_NULL_PTR(type))
  {
    fprintf(stderr, "[_dt_colorchecker_get_standard_type] Error: Invalid CGATS type provided.\n");
    result = g_strdup("Unknown Type");
  }
  else
  {
    dt_colorchecker_CGATS_types t = _dt_CGATS_get_type_value(type);
    if(t == CGATS_TYPE_IT8_7_1 || t == CGATS_TYPE_IT8_7_2)
      result = g_strdup("IT8"); // make a shorter title for the IT8 types
    else if(t == CGATS_TYPE_CTI3)
      result = g_strdup("CTI3");
    else
    {
      dt_print(DT_DEBUG_VERBOSE, "[_dt_colorchecker_get_standard_type] Unknown CGATS type: %s\n", type);
      result = g_strdup(type);
    }
  }
 
  if(IS_NULL_PTR(result))
  {
    fprintf(stderr, "[_dt_colorchecker_get_standard_type] Error: Memory allocation failed for standard type string.\n");
    return NULL;
  }
 
  return result;
}
 
static gboolean _dt_CGATS_is_supported(const cmsHANDLE *hIT8)
{
  if(IS_NULL_PTR(hIT8) || IS_NULL_PTR(*hIT8))
  {
    fprintf(stderr, "[_dt_CGATS_is_supported] Error: Invalid IT8 handle provided.\n");
    return FALSE;
  }
 
  const char *CGATS_type = cmsIT8GetSheetType(*hIT8);
  // The CGATS property stores the file syntax version, for example
  // "CGATS.17". The sheet type stores the target family we support,
  // for example "IT8.7/1" or "IT8.7/2".
  if(_dt_CGATS_get_type_value(CGATS_type) == CGATS_TYPE_UNKOWN)
  {
    dt_print(DT_DEBUG_VERBOSE, "[_dt_CGATS_is_supported] type '%s' is not supported by Ansel.\n",
             !IS_NULL_PTR(CGATS_type) ? CGATS_type : "(null)");
    return FALSE;
  }
 
  int column_SAMPLE_ID = -1;
  int column_X = -1;
  int column_Y = -1;
  int column_Z = -1;
  int column_L = -1;
  int column_a = -1;
  int column_b = -1;
  char **sample_names = NULL;
  int n_columns = cmsIT8EnumDataFormat(*hIT8, &sample_names);
 
  if(n_columns == -1)
  {
    fprintf(stderr, "[_dt_CGATS_is_supported] Error with the CGATS file, can't get column types\n");
    return FALSE;
  }
 
  if(!IS_NULL_PTR(sample_names))
    for(int i = 0; i < n_columns; i++)
    {
      if(!g_strcmp0(sample_names[i], "SAMPLE_ID") || !g_strcmp0(sample_names[i], "SAMPLE_LOC"))
        column_SAMPLE_ID = i;
      else if(!g_strcmp0(sample_names[i], "XYZ_X"))
        column_X = i;
      else if(!g_strcmp0(sample_names[i], "XYZ_Y"))
        column_Y = i;
      else if(!g_strcmp0(sample_names[i], "XYZ_Z"))
        column_Z = i;
      else if(!g_strcmp0(sample_names[i], "LAB_L"))
        column_L = i;
      else if(!g_strcmp0(sample_names[i], "LAB_A"))
        column_a = i;
      else if(!g_strcmp0(sample_names[i], "LAB_B"))
        column_b = i;
    }
 
  if(column_SAMPLE_ID == -1)
  {
    fprintf(stderr, "[_dt_CGATS_is_supported] Error: can't find the SAMPLE_ID column in the CGATS file.\n");
    return FALSE;
  }
 
  if(column_X + column_Y + column_Z + column_L + column_a + column_b == -1)
  {
    fprintf(stderr, "[_dt_CGATS_is_supported] Error: No XYZ or Lab columns found in the CGATS file.\n");
    return FALSE;
  }
 
  uint32_t table_count = cmsIT8TableCount(*hIT8);
  if(table_count != 1)
  {
    dt_print(DT_DEBUG_VERBOSE, "[_dt_CGATS_is_supported] the CGATS file contains %u tables but only one table is supported at the moment.\n",
             table_count);
    return FALSE;
  }
 
  return TRUE;
}
 
static inline const char *_dt_CGATS_get_author(const cmsHANDLE *hIT8)
{
  if(IS_NULL_PTR(hIT8) || IS_NULL_PTR(*hIT8))
  {
    fprintf(stderr, "[_dt_CGATS_get_author] Error: Invalid IT8 handle provided.\n");
    return "Unknown Author";
  }
  const char *author = cmsIT8GetProperty(*hIT8, "ORIGINATOR");
 
  return !IS_NULL_PTR(author) ? author : "Unknown Author";
}
 
static inline const char *_dt_CGATS_get_date(const cmsHANDLE *hIT8)
{
  if(IS_NULL_PTR(hIT8) || IS_NULL_PTR(*hIT8))
  {
    fprintf(stderr, "[_dt_CGATS_get_date] Error: Invalid IT8 handle provided.\n");
    return "Unknown Date";
  }
 
  // in CGATS.17, the date in PROD_DATE is stored in the format YYYY:MM
  const char *date = cmsIT8GetProperty(*hIT8, "PROD_DATE");
 
  return !IS_NULL_PTR(date) ? date : "Unknown Date";
}
 
static inline const char *_dt_CGATS_get_manufacturer(const cmsHANDLE *hIT8)
{
  if(IS_NULL_PTR(hIT8) || IS_NULL_PTR(*hIT8))
  {
    fprintf(stderr, "[_dt_CGATS_get_manufacturer] Error: Invalid IT8 handle provided.\n");
    return "Unknown Manufacturer";
  }
  const char *manufacturer = cmsIT8GetProperty(*hIT8, "MANUFACTURER");
  return !IS_NULL_PTR(manufacturer) ? manufacturer : "Unknown Manufacturer";
}
 
static inline gchar *_dt_get_builtin_colorchecker_name(const dt_color_checker_targets target_type)
{
  dt_color_checker_t *color_checker = dt_get_color_checker(target_type, NULL, NULL);
  if(IS_NULL_PTR(color_checker))
  {
    fprintf(stderr, "[_dt_get_builtin_colorchecker_name] Error: Unable to get the color checker %d.\n", target_type);
    return g_strdup("Unknown name");
  }
  gchar *name = g_strdup(color_checker->name);
 
  dt_colorchecker_cleanup(color_checker);
  return !IS_NULL_PTR(name) ? name : g_strdup("Unknown name");
}
 
static inline int _dt_get_builtin_colorchecker_patch_nb(const dt_color_checker_targets target_type)
{
  dt_color_checker_t *color_checker = dt_get_color_checker(target_type, NULL, NULL);
  if(IS_NULL_PTR(color_checker))
  {
    fprintf(stderr, "[_dt_get_builtin_colorchecker_patch_nb] Error: Unable to get the color checker %d.\n", target_type);
    return 0;
  }
  const int patch_nb = color_checker->patches;
 
  dt_colorchecker_cleanup(color_checker);
  return patch_nb;
}
 
static gchar *_dt_colorchecker_label_build_name(const dt_colorchecker_CGATS_label_make_name_t *label)
{
  if(IS_NULL_PTR(label))
  {
    fprintf(stderr, "[_dt_colorchecker_label_build_name] Error: Invalid label provided.\n");
    return g_strdup("Unknown Color Checker");
  }
  const gchar *type = !IS_NULL_PTR(label->type) && g_strcmp0(label->type, "") != 0 ? label->type : "?";
  // material if any
  gchar *tmp_material = !IS_NULL_PTR(label->material) && g_strcmp0(label->material, "") != 0
                           ? g_strdup_printf(" (%s)", label->material)
                           : g_strdup("");
  // Description if any
  gchar *tmp_description = !IS_NULL_PTR(label->description) && g_strcmp0(label->description, "") != 0
                             ? g_strdup(label->description)
                             : g_strdup("Unknown");
 
  // Compose: filename
  gchar *name = g_strdup_printf("%s%s - %s", type, tmp_material, tmp_description);
 
  // Clean up
  dt_free(tmp_material)
  dt_free(tmp_description)
 
  return name;
}
 
static inline char *_dt_CGATS_get_name(const cmsHANDLE *hIT8, const char *filename)
{
  gchar *result = NULL;
  gchar *basename = NULL;
 
  if(!IS_NULL_PTR(filename) && g_strcmp0(filename, "") != 0)
  {
    basename = g_path_get_basename(filename);
    char *dot = g_strrstr(basename, ".");
    if(!IS_NULL_PTR(dot))
    {
      // remove the file extension
      *dot = '\0';
    }
  }
 
  if(IS_NULL_PTR(hIT8) || IS_NULL_PTR(*hIT8))
  {
    fprintf(stderr, "[_dt_CGATS_get_name] Error: Invalid CGATS handle provided.\n");
    result = g_strdup(!IS_NULL_PTR(basename) ? basename : "Unnamed CGATS");
  }
  else
  {
    // Get other useful information from the CGATS file
    gchar *chart_type = _dt_colorchecker_get_standard_type(cmsIT8GetSheetType(*hIT8));
    const char *description = cmsIT8GetProperty(*hIT8, "DESCRIPTOR");
    const dt_colorchecker_material_types material = _dt_colorchecker_IT8_get_material_type(hIT8);
    gchar *material_str = g_strdup(_dt_colorchecker_get_material_string(material));
 
    if(IS_NULL_PTR(chart_type) && IS_NULL_PTR(description) && IS_NULL_PTR(material_str))
    {
      dt_print(DT_DEBUG_VERBOSE, "[_dt_CGATS_get_name] no useful metadata found in the CGATS file to build a name, using filename instead.\n");
      result = (!IS_NULL_PTR(basename) && g_strcmp0(basename, "") != 0) ? g_strdup(basename) : g_strdup("Unnamed CGATS");
    }
    else
    {
      const dt_colorchecker_CGATS_label_make_name_t label = {
                                                        .type = chart_type,
                                                        .description = !IS_NULL_PTR(description) ? description : NULL,
                                                        .material = material_str }; //can be NULL
 
      gchar *name = _dt_colorchecker_label_build_name(&label);
 
      if(!IS_NULL_PTR(name) && g_strcmp0(name, "") != 0)
        result = name;
      else
      {
        result = (!IS_NULL_PTR(basename) && g_strcmp0(basename, "") != 0) ? g_strdup(basename) : g_strdup("Unnamed CGATS");
        dt_free(name)
      }
    }
 
    dt_free(chart_type)
    dt_free(material_str)
  }
 
  dt_free(basename)
 
  return result;
}
 
static int _dt_colorchecker_cht_get_patch_nb(const char *filepath)
{
  int result = 0;
  dt_colorchecker_chart_spec_t *chart_spec = NULL;
 
  if(IS_NULL_PTR(filepath) || g_strcmp0(filepath, "") == 0)
  {
    fprintf(stderr, "Error: Invalid file path provided for CHT file.\n");
    goto end;
  }
 
  chart_spec = _dt_colorchecker_chart_spec_init();
  if(IS_NULL_PTR(chart_spec))
  {
    fprintf(stderr, "Error: cannot allocate memory for the chart spec.\n");
    goto end;
  }
 
  if(!_dt_colorchecker_open_cht(filepath, chart_spec))
  {
    fprintf(stderr, "Error: cannot open the cht file '%s'.\n", filepath);
    goto end;
  }
 
  if(!chart_spec->num_patches)
    fprintf(stderr, "Error: no patches found in the cht file '%s'.\n", filepath);
  else result = chart_spec->num_patches;
 
  end:
  if(!IS_NULL_PTR(chart_spec)) _dt_colorchecker_chart_spec_cleanup(chart_spec);
  return result;
}
 
static float dE_1976(const float a, const float b, const float c)
{
  return sqrtf(sqf(a) + sqf(b) + sqf(c));
}
 
static inline void _dt_CGATS_find_whitest_blackest_greyest(const dt_color_checker_patch *const values, size_t *bwg, const size_t patch)
{
  if(IS_NULL_PTR(values) || IS_NULL_PTR(bwg))
  {
    fprintf(stderr, "[_dt_CGATS_find_whitest_blackest_greyest] Error: Invalid input parameters.\n");
    return;
  }
 
  for(int i = 0; i < 3; i++)
  {
    float target = 50.f * i;
    float delta_current = dE_1976(values[bwg[i]].Lab[0] - target, values[bwg[i]].Lab[1], values[bwg[i]].Lab[2]);
    float delta_patch = dE_1976(values[patch].Lab[0] - target, values[patch].Lab[1], values[patch].Lab[2]);
    if(delta_patch < delta_current)
      bwg[i] = patch;
  }
}
 
static dt_color_checker_patch *_dt_colorchecker_CGATS_fill_patch_values(const cmsHANDLE hIT8, size_t *bwg, const dt_colorchecker_chart_spec_t *chart_spec, const size_t num_patches)
{
  if(IS_NULL_PTR(hIT8) || IS_NULL_PTR(bwg) || IS_NULL_PTR(chart_spec) || num_patches == 0)
  {
    fprintf(stderr, "Error: Invalid input parameters for filling patch values from CGATS file.\n");
    return NULL;
  }
 
  int column_SAMPLE_ID = -1;
  int column_X = -1;
  int column_Y = -1;
  int column_Z = -1;
  int column_L = -1;
  int column_a = -1;
  int column_b = -1;
  char **sample_names = NULL;
  int n_columns = cmsIT8EnumDataFormat(hIT8, &sample_names);
 
  dt_color_checker_patch *values = dt_colorchecker_patch_array_init(num_patches);
  if(IS_NULL_PTR(values))
  {
    fprintf(stderr, "Error: Memory allocation failed for values array.\n");
    goto error;
  }
 
  gboolean use_XYZ = FALSE;
  if(n_columns == -1)
  {
    fprintf(stderr, "Error with the CGATS file, can't get column types\n");
    goto error;
  }
 
  for(int i = 0; i < n_columns; i++)
  {
    if(!g_strcmp0(sample_names[i], "SAMPLE_ID") || !g_strcmp0(sample_names[i], "SAMPLE_LOC"))
      column_SAMPLE_ID = i;
    else if(!g_strcmp0(sample_names[i], "XYZ_X"))
      column_X = i;
    else if(!g_strcmp0(sample_names[i], "XYZ_Y"))
      column_Y = i;
    else if(!g_strcmp0(sample_names[i], "XYZ_Z"))
      column_Z = i;
    else if(!g_strcmp0(sample_names[i], "LAB_L"))
      column_L = i;
    else if(!g_strcmp0(sample_names[i], "LAB_A"))
      column_a = i;
    else if(!g_strcmp0(sample_names[i], "LAB_B"))
      column_b = i;
  }
 
  if(column_SAMPLE_ID == -1)
  {
    fprintf(stderr, "Error: can't find the SAMPLE_ID column in the CGATS file.\n");
    goto error;
  }
 
  if(column_X + column_Y + column_Z + column_L + column_a + column_b == -1)
  {
    fprintf(stderr, "Error: No XYZ or Lab columns found in the CGATS file.\n");
    goto error;
  }
 
  int columns[3] = { -1, -1, -1 };
  if(column_L != -1 && column_a != -1 && column_b != -1)
  {
    columns[0] = cmsIT8FindDataFormat(hIT8, "LAB_L");
    columns[1] = cmsIT8FindDataFormat(hIT8, "LAB_A");
    columns[2] = cmsIT8FindDataFormat(hIT8, "LAB_B");
  }
  // In case no Lab column is found, we assume the IT8 file has XYZ data
  else if(column_X != -1 && column_Y != -1 && column_Z != -1)
  {
    use_XYZ = TRUE;
    columns[0] = cmsIT8FindDataFormat(hIT8, "XYZ_X");
    columns[1] = cmsIT8FindDataFormat(hIT8, "XYZ_Y");
    columns[2] = cmsIT8FindDataFormat(hIT8, "XYZ_Z");
  }
  else
  {
    fprintf(stderr, "Error: can't find XYZ or Lab columns in the CGATS file\n");
    goto error;
  }
 
  for(size_t patch_iter = 0; patch_iter < num_patches; patch_iter++)
  {
    // Ensure the CGATS row exists before binding its values to the chart patch
    // at the same index. The display name comes from the chart geometry below,
    // so we must not allocate a temporary row name that gets overwritten.
    const char *sample_name = cmsIT8GetDataRowCol(hIT8, patch_iter, 0);
    if(IS_NULL_PTR(sample_name))
    {
      fprintf(stderr, "Error : can't find sample '%" G_GSIZE_FORMAT "' in CGATS file\n", patch_iter);
      goto error;
    }
 
    // set patch position
    // The position of the patch is given by the chart specification
    if(IS_NULL_PTR(chart_spec->patches))
    {
      fprintf(stderr, "Error: no patches found in the chart specification.\n");
      goto error;
    }
 
    const dt_color_checker_patch *p = (dt_color_checker_patch*)g_slist_nth_data(chart_spec->patches, (guint)patch_iter);
    if(IS_NULL_PTR(p))
    {
      fprintf(stderr, "Error: patch %" G_GSIZE_FORMAT " not found in chart specification.\n", patch_iter);
      goto error;
    }
    _dt_colorchecker_copy_patch(&values[patch_iter], p);
    if(IS_NULL_PTR(values[patch_iter].name))
    {
      fprintf(stderr, "Error: patch %" G_GSIZE_FORMAT " has no name in chart specification.\n", patch_iter);
      goto error;
    }
 
    // Copy color values
    const double patchdbl[3] = { cmsIT8GetDataRowColDbl(hIT8, (int)patch_iter, columns[0]),
                                 cmsIT8GetDataRowColDbl(hIT8, (int)patch_iter, columns[1]),
                                 cmsIT8GetDataRowColDbl(hIT8, (int)patch_iter, columns[2]) };
 
    // Convert to Lab when it's in XYZ
    if(use_XYZ)
    {
      const dt_aligned_pixel_t patch_color = { (float)patchdbl[0] * 0.01, (float)patchdbl[1] *0.01, (float)patchdbl[2] * 0.01, 0.0f };
      dt_XYZ_to_Lab(patch_color, values[patch_iter].Lab);
    }
    else
    {
      values[patch_iter].Lab[0] = (float)patchdbl[0];
      values[patch_iter].Lab[1] = (float)patchdbl[1];
      values[patch_iter].Lab[2] = (float)patchdbl[2];
    }
 
    _dt_CGATS_find_whitest_blackest_greyest(values, bwg, patch_iter);
  }
 
  goto end;
 
error:
  if(!IS_NULL_PTR(values))
  {
    for(size_t i = 0; i < num_patches; i++)
    {
      dt_colorchecker_patch_cleanup(&values[i]);
    }
    dt_free_align(values);
  }
  values = NULL;
 
end:
  return values;
}
 
dt_color_checker_t *dt_colorchecker_user_ref_create(const char *color_filename, const char *cht_filename)
{
  dt_colorchecker_chart_spec_t *chart_spec = NULL;
  dt_color_checker_t *checker = NULL;
 
  int lineno = 0;
 
  if(IS_NULL_PTR(color_filename) || g_strcmp0(color_filename, "") == 0)
  {
    fprintf(stderr, "Error: Invalid color filename provided.\n");
    return NULL;
  }
 
  if(!g_file_test(color_filename, G_FILE_TEST_IS_REGULAR))
  {
    fprintf(stderr, "Error: the color file '%s' does not exist or is not a regular file.\n", color_filename);
    return NULL;
  }
 
  cmsHANDLE hIT8 = cmsIT8LoadFromFile(NULL, color_filename);
 
  if(!_dt_CGATS_is_supported(&hIT8))
  {
    fprintf(stderr, "Ansel cannot load the CGATS file '%s'\n", color_filename);
    ERROR
  }
 
  chart_spec = _dt_colorchecker_chart_spec_init();
  if(IS_NULL_PTR(chart_spec))
  {
    fprintf(stderr, "Error: cannot allocate memory for the chart spec.\n");
    ERROR
  }
  // load the cht file if any
  if(!IS_NULL_PTR(cht_filename) && g_file_test(cht_filename, G_FILE_TEST_IS_REGULAR))
  {
    if(!_dt_colorchecker_open_cht(cht_filename, chart_spec))
    {
      fprintf(stderr, "Error: cannot open the cht file '%s'.\n", cht_filename);
      ERROR
    }
  }
  else dt_print(DT_DEBUG_VERBOSE, "invalid cht file '%s'.\n", cht_filename);
 
  // Check if the CGATS file contains the expected number of patches
  const int num_patches_it8 = (const int)cmsIT8GetPropertyDbl(hIT8, "NUMBER_OF_SETS");
 
  if(chart_spec->num_patches > 0 && num_patches_it8 != chart_spec->num_patches)
  {
    dt_print(DT_DEBUG_VERBOSE, "the number of patches in the CGATS file (%i) does not match the expected number (%i) in the cht file.\n",
             num_patches_it8, chart_spec->num_patches);
  }
 
  // Limit the number of patches to the minimum between the CGATS file and the chart specification to avoid overflow.
  const size_t num_patches = MIN(num_patches_it8, chart_spec->num_patches);
  dt_print(DT_DEBUG_VERBOSE, "%" PRIu64 " patches will be added to the chart\n", (uint64_t)num_patches);
 
  checker = dt_colorchecker_init();
  if(IS_NULL_PTR(checker))
  {
    fprintf(stderr, "Error: cannot allocate memory for the color checker.\n");
    ERROR
  }
 
  checker->name = _dt_CGATS_get_name(&hIT8, color_filename);
  checker->author = g_strdup(_dt_CGATS_get_author(&hIT8));
  checker->date = g_strdup(_dt_CGATS_get_date(&hIT8));
  checker->manufacturer = g_strdup(_dt_CGATS_get_manufacturer(&hIT8));
  checker->type = COLOR_CHECKER_USER_REF;
  checker->radius = chart_spec->radius;
  checker->ratio = chart_spec->ratio;
  checker->patches = num_patches;
  checker->size[0] = chart_spec->size[0];
  checker->size[1] = chart_spec->size[1];
  checker->middle_grey = chart_spec->middle_grey;
  checker->white = chart_spec->white;
  checker->black = chart_spec->black;
 
  // blackest, whitest and greyest patches will be found while filling the color values
  size_t bwg[3] = { 0, 0, 0 };
  checker->values = _dt_colorchecker_CGATS_fill_patch_values(hIT8, bwg, chart_spec, num_patches);
  if(IS_NULL_PTR(checker->values))
  {
    fprintf(stderr, "Error: cannot fill the color values from the CGATS file.\n");
    ERROR
  }
 
  checker->black = bwg[0];
  checker->white = bwg[1];
  checker->middle_grey = bwg[2];
  dt_print(DT_DEBUG_VERBOSE, _("blackest patch: %s, middle grey patch: %s, white patch: %s\n"),
           checker->values[bwg[0]].name, checker->values[bwg[1]].name, checker->values[bwg[2]].name);
 
  dt_print(DT_DEBUG_VERBOSE, _("it8 '%s' done\n"), color_filename);
  goto end;
 
error:
  fprintf(stderr, "Error creating user ref checker, in %s %s:%d\n", __FUNCTION__, __FILE__, lineno);
  dt_colorchecker_cleanup(checker);
  checker = NULL;
 
  end:
  if(!IS_NULL_PTR(chart_spec)) _dt_colorchecker_chart_spec_cleanup(chart_spec); // only allocated chart will be freed
  if(!IS_NULL_PTR(hIT8)) cmsIT8Free(hIT8);
  return checker;
}
 
static dt_colorchecker_label_t *_dt_colorchecker_user_ref_make_label(const gchar *filename, const gchar *user_it8_dir)
{
  dt_colorchecker_label_t *result = NULL;
 
  if(IS_NULL_PTR(filename) || g_strcmp0(filename, "") == 0 || IS_NULL_PTR(user_it8_dir) || g_strcmp0(user_it8_dir, "") == 0)
  {
    fprintf(stderr, "Error: Invalid filename or user IT8 directory provided for making CGATS label.\n");
    return NULL;
  }
 
  gchar *filepath = g_build_filename(user_it8_dir, filename, NULL);
  if(g_file_test(filepath, G_FILE_TEST_IS_REGULAR))
  {
    cmsHANDLE hIT8 = cmsIT8LoadFromFile(NULL, filepath);
    if(!IS_NULL_PTR(hIT8) && _dt_CGATS_is_supported(&hIT8))
    {
      const int patch_nb = (int)cmsIT8GetPropertyDbl(hIT8, "NUMBER_OF_SETS");
      if(patch_nb > 0)
      {
        gchar *label = _dt_CGATS_get_name(&hIT8, filename);
        dt_colorchecker_label_t *CGATS_label = dt_colorchecker_label_init(label, COLOR_CHECKER_USER_REF, filepath, patch_nb);
 
        dt_free(label);
        result = CGATS_label;
      }
    }
    if(!IS_NULL_PTR(hIT8)) cmsIT8Free(hIT8);
  }
  dt_free(filepath)
 
  if(IS_NULL_PTR(result))
    return NULL;
 
  else return result;
}
 
static dt_colorchecker_label_t *_dt_colorchecker_cht_make_label(const gchar *filename, const gchar *user_it8_dir)
{
  if(IS_NULL_PTR(filename) || g_strcmp0(filename, "") == 0 || IS_NULL_PTR(user_it8_dir) || g_strcmp0(user_it8_dir, "") == 0)
  {
    fprintf(stderr, "Error: Invalid filename or user IT8 directory provided for making CHT label.\n");
    return NULL;
  }
 
  dt_colorchecker_label_t *cht_label = NULL;
 
  gchar *filepath = g_build_filename(user_it8_dir, filename, NULL);
  if(g_file_test(filepath, G_FILE_TEST_IS_REGULAR))
  {
    gchar *basename = g_path_get_basename(filename);
    char *dot = g_strrstr(basename, ".");
    if(!IS_NULL_PTR(dot)) *dot = '\0'; // removes the file extension in basename
    const int patch_nb = _dt_colorchecker_cht_get_patch_nb(filepath);
 
    if(patch_nb > 0) // only create a label if the CHT file has patches
      cht_label = dt_colorchecker_label_init(basename, COLOR_CHECKER_USER_REF, filepath, patch_nb);
 
    dt_free(basename);
  }
  dt_free(filepath);
 
  return cht_label;
}
 
int dt_colorchecker_find_builtin(GList **colorcheckers_label)
{
  int nb = 0;
  for(int k = 0; k < COLOR_CHECKER_USER_REF; k++)
  {
    gchar *name = _dt_get_builtin_colorchecker_name(k);
    const int patch_nb = _dt_get_builtin_colorchecker_patch_nb(k);
    if(patch_nb <= 0)
    {
      dt_free(name)
      continue; // skip color checkers with no patches
    }
 
    dt_colorchecker_label_t *builtin_label = dt_colorchecker_label_init(name, k, NULL, patch_nb);
    dt_free(name)
 
    if(IS_NULL_PTR(builtin_label))
    {
      fprintf(stderr, "Error: failed to allocate memory for builtin colorchecker label %d\n", k);
      continue;
    }
    else
    {
      *colorcheckers_label = g_list_append(*colorcheckers_label, builtin_label);
      nb++;
    }
  }
  return nb;
}
 
int dt_colorchecker_find_CGATS_reference_files(GList **ref_colorcheckers_files)
{
  int nb = 0;
  char confdir[PATH_MAX] = { 0 };
  dt_loc_get_user_config_dir(confdir, sizeof(confdir));
  gchar *user_it8_dir = g_build_filename(confdir, "color", "checker", NULL);
 
  GDir *dir = g_dir_open(user_it8_dir, 0, NULL);
  if(!IS_NULL_PTR(dir))
  {
    const char *filename;
    while(!IS_NULL_PTR(filename = g_dir_read_name(dir)))
    {
      const char *dot = g_strrstr(filename, ".");
      if(!IS_NULL_PTR(dot) && g_ascii_strcasecmp(dot, ".cht") == 0)
        continue; // skip .cht files
 
      dt_colorchecker_label_t *CGATS_label = _dt_colorchecker_user_ref_make_label(filename, user_it8_dir);
      if(!IS_NULL_PTR(CGATS_label))
      {
        *ref_colorcheckers_files = g_list_append(*ref_colorcheckers_files, CGATS_label);
        nb++;
      }
      else
        dt_print(DT_DEBUG_VERBOSE, "failed to load CGATS file '%s' in %s\n", filename, user_it8_dir);
    }
    g_dir_close(dir);
  }
  dt_free(user_it8_dir)
 
  return nb;
}
 
int dt_colorchecker_find_cht_files(GList **chts)
{
  int nb = 0;
  char confdir[PATH_MAX] = { 0 };
  dt_loc_get_user_config_dir(confdir, sizeof(confdir));
  gchar *user_it8_dir = g_build_filename(confdir, "color", "checker", NULL);
 
  GDir *dir = g_dir_open(user_it8_dir, 0, NULL);
  if(!IS_NULL_PTR(dir))
  {
    const char *filename;
    while(!IS_NULL_PTR(filename = g_dir_read_name(dir)))
    {
      const char *dot = g_strrstr(filename, ".");
      if(IS_NULL_PTR(dot) || g_ascii_strcasecmp(dot, ".cht") != 0)
        continue; // skip files that are not .cht
 
      dt_colorchecker_label_t *cht_label = _dt_colorchecker_cht_make_label(filename, user_it8_dir);
      if(!IS_NULL_PTR(cht_label))
      {
        *chts = g_list_append(*chts, cht_label);
        nb++;
      }
    }
    g_dir_close(dir);
  }
  dt_free(user_it8_dir);
 
  return nb;
}
 
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