blender-archive/source/blender/imbuf/intern/png.c

/*
 * This program 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 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
 * All rights reserved.
 */

/** \file
 * \ingroup imbuf
 *
 * \todo Save floats as 16 bits per channel, currently readonly.
 */

#include "png.h"

#include "BLI_fileops.h"
#include "BLI_math.h"
#include "BLI_utildefines.h"

#include "BKE_global.h"
#include "BKE_idprop.h"

#include "DNA_ID.h" /* ID property definitions. */

#include "MEM_guardedalloc.h"

#include "IMB_imbuf.h"
#include "IMB_imbuf_types.h"

#include "IMB_allocimbuf.h"
#include "IMB_filetype.h"
#include "IMB_metadata.h"

#include "IMB_colormanagement.h"
#include "IMB_colormanagement_intern.h"

typedef struct PNGReadStruct {
  const unsigned char *data;
  unsigned int size;
  unsigned int seek;
} PNGReadStruct;

static void ReadData(png_structp png_ptr, png_bytep data, png_size_t length);
static void WriteData(png_structp png_ptr, png_bytep data, png_size_t length);
static void Flush(png_structp png_ptr);

BLI_INLINE unsigned short UPSAMPLE_8_TO_16(const unsigned char _val)
{
  return (_val << 8) + _val;
}

bool imb_is_a_png(const unsigned char *mem, size_t size)
{
  const int num_to_check = 8;
  if (size < num_to_check) {
    return false;
  }
  bool ok = false;

#if (PNG_LIBPNG_VER_MAJOR == 1) && (PNG_LIBPNG_VER_MINOR == 2)
  /* Older version of libpng doesn't use const pointer to memory. */
  ok = !png_sig_cmp((png_bytep)mem, 0, num_to_check);
#else
  ok = !png_sig_cmp(mem, 0, num_to_check);
#endif
  return ok;
}

static void Flush(png_structp png_ptr)
{
  (void)png_ptr;
}

static void WriteData(png_structp png_ptr, png_bytep data, png_size_t length)
{
  ImBuf *ibuf = (ImBuf *)png_get_io_ptr(png_ptr);

  /* if buffer is too small increase it. */
  while (ibuf->encodedsize + length > ibuf->encodedbuffersize) {
    imb_enlargeencodedbufferImBuf(ibuf);
  }

  memcpy(ibuf->encodedbuffer + ibuf->encodedsize, data, length);
  ibuf->encodedsize += length;
}

static void ReadData(png_structp png_ptr, png_bytep data, png_size_t length)
{
  PNGReadStruct *rs = (PNGReadStruct *)png_get_io_ptr(png_ptr);

  if (rs) {
    if (length <= rs->size - rs->seek) {
      memcpy(data, rs->data + rs->seek, length);
      rs->seek += length;
      return;
    }
  }

  printf("Reached EOF while decoding PNG\n");
  longjmp(png_jmpbuf(png_ptr), 1);
}

static float channel_colormanage_noop(float value)
{
  return value;
}

/* wrap to avoid macro calling functions multiple times */
BLI_INLINE unsigned short ftoshort(float val)
{
  return unit_float_to_ushort_clamp(val);
}

bool imb_savepng(struct ImBuf *ibuf, const char *filepath, int flags)
{
  png_structp png_ptr;
  png_infop info_ptr;

  unsigned char *pixels = NULL;
  unsigned char *from, *to;
  unsigned short *pixels16 = NULL, *to16;
  float *from_float, from_straight[4];
  png_bytepp row_pointers = NULL;
  int i, bytesperpixel, color_type = PNG_COLOR_TYPE_GRAY;
  FILE *fp = NULL;

  bool is_16bit = (ibuf->foptions.flag & PNG_16BIT) != 0;
  bool has_float = (ibuf->rect_float != NULL);
  int channels_in_float = ibuf->channels ? ibuf->channels : 4;

  float (*chanel_colormanage_cb)(float);
  size_t num_bytes;

  /* use the jpeg quality setting for compression */
  int compression;
  compression = (int)(((float)(ibuf->foptions.quality) / 11.1111f));
  compression = compression < 0 ? 0 : (compression > 9 ? 9 : compression);

  if (ibuf->float_colorspace || (ibuf->colormanage_flag & IMB_COLORMANAGE_IS_DATA)) {
    /* float buffer was managed already, no need in color space conversion */
    chanel_colormanage_cb = channel_colormanage_noop;
  }
  else {
    /* standard linear-to-srgb conversion if float buffer wasn't managed */
    chanel_colormanage_cb = linearrgb_to_srgb;
  }

  /* for prints */
  if (flags & IB_mem) {
    filepath = "<memory>";
  }

  bytesperpixel = (ibuf->planes + 7) >> 3;
  if ((bytesperpixel > 4) || (bytesperpixel == 2)) {
    printf(
        "imb_savepng: Unsupported bytes per pixel: %d for file: '%s'\n", bytesperpixel, filepath);
    return 0;
  }

  png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
  if (png_ptr == NULL) {
    printf("imb_savepng: Cannot png_create_write_struct for file: '%s'\n", filepath);
    return 0;
  }

  info_ptr = png_create_info_struct(png_ptr);
  if (info_ptr == NULL) {
    png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
    printf("imb_savepng: Cannot png_create_info_struct for file: '%s'\n", filepath);
    return 0;
  }

  /* copy image data */
  num_bytes = ((size_t)ibuf->x) * ibuf->y * bytesperpixel;
  if (is_16bit) {
    pixels16 = MEM_mallocN(num_bytes * sizeof(unsigned short), "png 16bit pixels");
  }
  else {
    pixels = MEM_mallocN(num_bytes * sizeof(unsigned char), "png 8bit pixels");
  }
  if (pixels == NULL && pixels16 == NULL) {
    printf(
        "imb_savepng: Cannot allocate pixels array of %dx%d, %d bytes per pixel for file: "
        "'%s'\n",
        ibuf->x,
        ibuf->y,
        bytesperpixel,
        filepath);
  }

  /* allocate memory for an array of row-pointers */
  row_pointers = (png_bytepp)MEM_mallocN(ibuf->y * sizeof(png_bytep), "row_pointers");
  if (row_pointers == NULL) {
    printf("imb_savepng: Cannot allocate row-pointers array for file '%s'\n", filepath);
  }

  if ((pixels == NULL && pixels16 == NULL) || (row_pointers == NULL) ||
      setjmp(png_jmpbuf(png_ptr))) {
    /* On error jump here, and free any resources. */
    png_destroy_write_struct(&png_ptr, &info_ptr);
    if (pixels) {
      MEM_freeN(pixels);
    }
    if (pixels16) {
      MEM_freeN(pixels16);
    }
    if (row_pointers) {
      MEM_freeN(row_pointers);
    }
    if (fp) {
      fflush(fp);
      fclose(fp);
    }
    return 0;
  }

  from = (unsigned char *)ibuf->rect;
  to = pixels;
  from_float = ibuf->rect_float;
  to16 = pixels16;

  switch (bytesperpixel) {
    case 4:
      color_type = PNG_COLOR_TYPE_RGBA;
      if (is_16bit) {
        if (has_float) {
          if (channels_in_float == 4) {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              premul_to_straight_v4_v4(from_straight, from_float);
              to16[0] = ftoshort(chanel_colormanage_cb(from_straight[0]));
              to16[1] = ftoshort(chanel_colormanage_cb(from_straight[1]));
              to16[2] = ftoshort(chanel_colormanage_cb(from_straight[2]));
              to16[3] = ftoshort(chanel_colormanage_cb(from_straight[3]));
              to16 += 4;
              from_float += 4;
            }
          }
          else if (channels_in_float == 3) {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              to16[0] = ftoshort(chanel_colormanage_cb(from_float[0]));
              to16[1] = ftoshort(chanel_colormanage_cb(from_float[1]));
              to16[2] = ftoshort(chanel_colormanage_cb(from_float[2]));
              to16[3] = 65535;
              to16 += 4;
              from_float += 3;
            }
          }
          else {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              to16[0] = ftoshort(chanel_colormanage_cb(from_float[0]));
              to16[2] = to16[1] = to16[0];
              to16[3] = 65535;
              to16 += 4;
              from_float++;
            }
          }
        }
        else {
          for (i = ibuf->x * ibuf->y; i > 0; i--) {
            to16[0] = UPSAMPLE_8_TO_16(from[0]);
            to16[1] = UPSAMPLE_8_TO_16(from[1]);
            to16[2] = UPSAMPLE_8_TO_16(from[2]);
            to16[3] = UPSAMPLE_8_TO_16(from[3]);
            to16 += 4;
            from += 4;
          }
        }
      }
      else {
        for (i = ibuf->x * ibuf->y; i > 0; i--) {
          to[0] = from[0];
          to[1] = from[1];
          to[2] = from[2];
          to[3] = from[3];
          to += 4;
          from += 4;
        }
      }
      break;
    case 3:
      color_type = PNG_COLOR_TYPE_RGB;
      if (is_16bit) {
        if (has_float) {
          if (channels_in_float == 4) {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              premul_to_straight_v4_v4(from_straight, from_float);
              to16[0] = ftoshort(chanel_colormanage_cb(from_straight[0]));
              to16[1] = ftoshort(chanel_colormanage_cb(from_straight[1]));
              to16[2] = ftoshort(chanel_colormanage_cb(from_straight[2]));
              to16 += 3;
              from_float += 4;
            }
          }
          else if (channels_in_float == 3) {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              to16[0] = ftoshort(chanel_colormanage_cb(from_float[0]));
              to16[1] = ftoshort(chanel_colormanage_cb(from_float[1]));
              to16[2] = ftoshort(chanel_colormanage_cb(from_float[2]));
              to16 += 3;
              from_float += 3;
            }
          }
          else {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              to16[0] = ftoshort(chanel_colormanage_cb(from_float[0]));
              to16[2] = to16[1] = to16[0];
              to16 += 3;
              from_float++;
            }
          }
        }
        else {
          for (i = ibuf->x * ibuf->y; i > 0; i--) {
            to16[0] = UPSAMPLE_8_TO_16(from[0]);
            to16[1] = UPSAMPLE_8_TO_16(from[1]);
            to16[2] = UPSAMPLE_8_TO_16(from[2]);
            to16 += 3;
            from += 4;
          }
        }
      }
      else {
        for (i = ibuf->x * ibuf->y; i > 0; i--) {
          to[0] = from[0];
          to[1] = from[1];
          to[2] = from[2];
          to += 3;
          from += 4;
        }
      }
      break;
    case 1:
      color_type = PNG_COLOR_TYPE_GRAY;
      if (is_16bit) {
        if (has_float) {
          float rgb[3];
          if (channels_in_float == 4) {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              premul_to_straight_v4_v4(from_straight, from_float);
              rgb[0] = chanel_colormanage_cb(from_straight[0]);
              rgb[1] = chanel_colormanage_cb(from_straight[1]);
              rgb[2] = chanel_colormanage_cb(from_straight[2]);
              to16[0] = ftoshort(IMB_colormanagement_get_luminance(rgb));
              to16++;
              from_float += 4;
            }
          }
          else if (channels_in_float == 3) {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              rgb[0] = chanel_colormanage_cb(from_float[0]);
              rgb[1] = chanel_colormanage_cb(from_float[1]);
              rgb[2] = chanel_colormanage_cb(from_float[2]);
              to16[0] = ftoshort(IMB_colormanagement_get_luminance(rgb));
              to16++;
              from_float += 3;
            }
          }
          else {
            for (i = ibuf->x * ibuf->y; i > 0; i--) {
              to16[0] = ftoshort(chanel_colormanage_cb(from_float[0]));
              to16++;
              from_float++;
            }
          }
        }
        else {
          for (i = ibuf->x * ibuf->y; i > 0; i--) {
            to16[0] = UPSAMPLE_8_TO_16(from[0]);
            to16++;
            from += 4;
          }
        }
      }
      else {
        for (i = ibuf->x * ibuf->y; i > 0; i--) {
          to[0] = from[0];
          to++;
          from += 4;
        }
      }
      break;
  }

  if (flags & IB_mem) {
    /* create image in memory */
    imb_addencodedbufferImBuf(ibuf);
    ibuf->encodedsize = 0;

    png_set_write_fn(png_ptr, (png_voidp)ibuf, WriteData, Flush);
  }
  else {
    fp = BLI_fopen(filepath, "wb");
    if (!fp) {
      png_destroy_write_struct(&png_ptr, &info_ptr);
      if (pixels) {
        MEM_freeN(pixels);
      }
      if (pixels16) {
        MEM_freeN(pixels16);
      }
      MEM_freeN(row_pointers);
      printf("imb_savepng: Cannot open file for writing: '%s'\n", filepath);
      return 0;
    }
    png_init_io(png_ptr, fp);
  }

#if 0
  png_set_filter(png_ptr,
                 0,
                 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE | PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
                     PNG_FILTER_UP | PNG_FILTER_VALUE_UP | PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
                     PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH | PNG_ALL_FILTERS);
#endif

  png_set_compression_level(png_ptr, compression);

  /* png image settings */
  png_set_IHDR(png_ptr,
               info_ptr,
               ibuf->x,
               ibuf->y,
               is_16bit ? 16 : 8,
               color_type,
               PNG_INTERLACE_NONE,
               PNG_COMPRESSION_TYPE_DEFAULT,
               PNG_FILTER_TYPE_DEFAULT);

  /* image text info */
  if (ibuf->metadata) {
    png_text *metadata;
    IDProperty *prop;

    int num_text = 0;

    for (prop = ibuf->metadata->data.group.first; prop; prop = prop->next) {
      if (prop->type == IDP_STRING) {
        num_text++;
      }
    }

    metadata = MEM_callocN(num_text * sizeof(png_text), "png_metadata");
    num_text = 0;
    for (prop = ibuf->metadata->data.group.first; prop; prop = prop->next) {
      if (prop->type == IDP_STRING) {
        metadata[num_text].compression = PNG_TEXT_COMPRESSION_NONE;
        metadata[num_text].key = prop->name;
        metadata[num_text].text = IDP_String(prop);
        num_text++;
      }
    }

    png_set_text(png_ptr, info_ptr, metadata, num_text);
    MEM_freeN(metadata);
  }

  if (ibuf->ppm[0] > 0.0 && ibuf->ppm[1] > 0.0) {
    png_set_pHYs(png_ptr,
                 info_ptr,
                 (unsigned int)(ibuf->ppm[0] + 0.5),
                 (unsigned int)(ibuf->ppm[1] + 0.5),
                 PNG_RESOLUTION_METER);
  }

  /* write the file header information */
  png_write_info(png_ptr, info_ptr);

#ifdef __LITTLE_ENDIAN__
  png_set_swap(png_ptr);
#endif

  /* set the individual row-pointers to point at the correct offsets */
  if (is_16bit) {
    for (i = 0; i < ibuf->y; i++) {
      row_pointers[ibuf->y - 1 - i] = (png_bytep)((unsigned short *)pixels16 +
                                                  (((size_t)i) * ibuf->x) * bytesperpixel);
    }
  }
  else {
    for (i = 0; i < ibuf->y; i++) {
      row_pointers[ibuf->y - 1 - i] = (png_bytep)((unsigned char *)pixels +
                                                  (((size_t)i) * ibuf->x) * bytesperpixel *
                                                      sizeof(unsigned char));
    }
  }

  /* write out the entire image data in one call */
  png_write_image(png_ptr, row_pointers);

  /* write the additional chunks to the PNG file (not really needed) */
  png_write_end(png_ptr, info_ptr);

  /* clean up */
  if (pixels) {
    MEM_freeN(pixels);
  }
  if (pixels16) {
    MEM_freeN(pixels16);
  }
  MEM_freeN(row_pointers);
  png_destroy_write_struct(&png_ptr, &info_ptr);

  if (fp) {
    fflush(fp);
    fclose(fp);
  }

  return 1;
}

static void imb_png_warning(png_structp UNUSED(png_ptr), png_const_charp message)
{
  /* We suppress iCCP warnings. That's how Blender always used to behave,
   * and with new libpng it became too much picky, giving a warning on
   * the splash screen even.
   */
  if ((G.debug & G_DEBUG) == 0 && STRPREFIX(message, "iCCP")) {
    return;
  }
  fprintf(stderr, "libpng warning: %s\n", message);
}

static void imb_png_error(png_structp UNUSED(png_ptr), png_const_charp message)
{
  fprintf(stderr, "libpng error: %s\n", message);
}

ImBuf *imb_loadpng(const unsigned char *mem, size_t size, int flags, char colorspace[IM_MAX_SPACE])
{
  struct ImBuf *ibuf = NULL;
  png_structp png_ptr;
  png_infop info_ptr;
  unsigned char *pixels = NULL;
  unsigned short *pixels16 = NULL;
  png_bytepp row_pointers = NULL;
  png_uint_32 width, height;
  int bit_depth, color_type;
  PNGReadStruct ps;

  unsigned char *from, *to;
  unsigned short *from16;
  float *to_float;
  unsigned int channels;

  if (imb_is_a_png(mem, size) == 0) {
    return NULL;
  }

  /* both 8 and 16 bit PNGs are default to standard byte colorspace */
  colorspace_set_default_role(colorspace, IM_MAX_SPACE, COLOR_ROLE_DEFAULT_BYTE);

  png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
  if (png_ptr == NULL) {
    printf("Cannot png_create_read_struct\n");
    return NULL;
  }

  png_set_error_fn(png_ptr, NULL, imb_png_error, imb_png_warning);

  info_ptr = png_create_info_struct(png_ptr);
  if (info_ptr == NULL) {
    png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
    printf("Cannot png_create_info_struct\n");
    return NULL;
  }

  ps.size = size; /* XXX, 4gig limit! */
  ps.data = mem;
  ps.seek = 0;

  png_set_read_fn(png_ptr, (void *)&ps, ReadData);

  if (setjmp(png_jmpbuf(png_ptr))) {
    /* On error jump here, and free any resources. */
    png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
    if (pixels) {
      MEM_freeN(pixels);
    }
    if (pixels16) {
      MEM_freeN(pixels16);
    }
    if (row_pointers) {
      MEM_freeN(row_pointers);
    }
    if (ibuf) {
      IMB_freeImBuf(ibuf);
    }
    return NULL;
  }

  // png_set_sig_bytes(png_ptr, 8);

  png_read_info(png_ptr, info_ptr);
  png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, NULL, NULL, NULL);

  channels = png_get_channels(png_ptr, info_ptr);

  switch (color_type) {
    case PNG_COLOR_TYPE_RGB:
    case PNG_COLOR_TYPE_RGB_ALPHA:
      break;
    case PNG_COLOR_TYPE_PALETTE:
      png_set_palette_to_rgb(png_ptr);
      if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
        channels = 4;
      }
      else {
        channels = 3;
      }
      break;
    case PNG_COLOR_TYPE_GRAY:
    case PNG_COLOR_TYPE_GRAY_ALPHA:
      if (bit_depth < 8) {
        png_set_expand(png_ptr);
        bit_depth = 8;
        if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
          /* PNG_COLOR_TYPE_GRAY may also have alpha 'values', like with palette. */
          channels = 2;
        }
      }
      break;
    default:
      printf("PNG format not supported\n");
      longjmp(png_jmpbuf(png_ptr), 1);
  }

  ibuf = IMB_allocImBuf(width, height, 8 * channels, 0);

  if (ibuf) {
    ibuf->ftype = IMB_FTYPE_PNG;
    if (bit_depth == 16) {
      ibuf->foptions.flag |= PNG_16BIT;
    }

    if (png_get_valid(png_ptr, info_ptr, PNG_INFO_pHYs)) {
      int unit_type;
      png_uint_32 xres, yres;

      if (png_get_pHYs(png_ptr, info_ptr, &xres, &yres, &unit_type)) {
        if (unit_type == PNG_RESOLUTION_METER) {
          ibuf->ppm[0] = xres;
          ibuf->ppm[1] = yres;
        }
      }
    }
  }
  else {
    printf("Couldn't allocate memory for PNG image\n");
  }

  if (ibuf && ((flags & IB_test) == 0)) {
    if (bit_depth == 16) {
      imb_addrectfloatImBuf(ibuf);
      png_set_swap(png_ptr);

      pixels16 = imb_alloc_pixels(ibuf->x, ibuf->y, channels, sizeof(png_uint_16), "pixels");
      if (pixels16 == NULL || ibuf->rect_float == NULL) {
        printf("Cannot allocate pixels array\n");
        longjmp(png_jmpbuf(png_ptr), 1);
      }

      /* allocate memory for an array of row-pointers */
      row_pointers = (png_bytepp)MEM_mallocN((size_t)ibuf->y * sizeof(png_uint_16p),
                                             "row_pointers");
      if (row_pointers == NULL) {
        printf("Cannot allocate row-pointers array\n");
        longjmp(png_jmpbuf(png_ptr), 1);
      }

      /* set the individual row-pointers to point at the correct offsets */
      for (size_t i = 0; i < ibuf->y; i++) {
        row_pointers[ibuf->y - 1 - i] = (png_bytep)((png_uint_16 *)pixels16 +
                                                    (i * ibuf->x) * channels);
      }

      png_read_image(png_ptr, row_pointers);

      /* copy image data */

      to_float = ibuf->rect_float;
      from16 = pixels16;

      switch (channels) {
        case 4:
          for (size_t i = (size_t)ibuf->x * (size_t)ibuf->y; i > 0; i--) {
            to_float[0] = from16[0] / 65535.0;
            to_float[1] = from16[1] / 65535.0;
            to_float[2] = from16[2] / 65535.0;
            to_float[3] = from16[3] / 65535.0;
            to_float += 4;
            from16 += 4;
          }
          break;
        case 3:
          for (size_t i = (size_t)ibuf->x * (size_t)ibuf->y; i > 0; i--) {
            to_float[0] = from16[0] / 65535.0;
            to_float[1] = from16[1] / 65535.0;
            to_float[2] = from16[2] / 65535.0;
            to_float[3] = 1.0;
            to_float += 4;
            from16 += 3;
          }
          break;
        case 2:
          for (size_t i = (size_t)ibuf->x * (size_t)ibuf->y; i > 0; i--) {
            to_float[0] = to_float[1] = to_float[2] = from16[0] / 65535.0;
            to_float[3] = from16[1] / 65535.0;
            to_float += 4;
            from16 += 2;
          }
          break;
        case 1:
          for (size_t i = (size_t)ibuf->x * (size_t)ibuf->y; i > 0; i--) {
            to_float[0] = to_float[1] = to_float[2] = from16[0] / 65535.0;
            to_float[3] = 1.0;
            to_float += 4;
            from16++;
          }
          break;
      }
    }
    else {
      imb_addrectImBuf(ibuf);

      pixels = imb_alloc_pixels(ibuf->x, ibuf->y, channels, sizeof(unsigned char), "pixels");
      if (pixels == NULL || ibuf->rect == NULL) {
        printf("Cannot allocate pixels array\n");
        longjmp(png_jmpbuf(png_ptr), 1);
      }

      /* allocate memory for an array of row-pointers */
      row_pointers = (png_bytepp)MEM_mallocN((size_t)ibuf->y * sizeof(png_bytep), "row_pointers");
      if (row_pointers == NULL) {
        printf("Cannot allocate row-pointers array\n");
        longjmp(png_jmpbuf(png_ptr), 1);
      }

      /* set the individual row-pointers to point at the correct offsets */
      for (int i = 0; i < ibuf->y; i++) {
        row_pointers[ibuf->y - 1 - i] = (png_bytep)(
            (unsigned char *)pixels + (((size_t)i) * ibuf->x) * channels * sizeof(unsigned char));
      }

      png_read_image(png_ptr, row_pointers);

      /* copy image data */

      to = (unsigned char *)ibuf->rect;
      from = pixels;

      switch (channels) {
        case 4:
          for (size_t i = (size_t)ibuf->x * (size_t)ibuf->y; i > 0; i--) {
            to[0] = from[0];
            to[1] = from[1];
            to[2] = from[2];
            to[3] = from[3];
            to += 4;
            from += 4;
          }
          break;
        case 3:
          for (size_t i = (size_t)ibuf->x * (size_t)ibuf->y; i > 0; i--) {
            to[0] = from[0];
            to[1] = from[1];
            to[2] = from[2];
            to[3] = 0xff;
            to += 4;
            from += 3;
          }
          break;
        case 2:
          for (size_t i = (size_t)ibuf->x * (size_t)ibuf->y; i > 0; i--) {
            to[0] = to[1] = to[2] = from[0];
            to[3] = from[1];
            to += 4;
            from += 2;
          }
          break;
        case 1:
          for (size_t i = (size_t)ibuf->x * (size_t)ibuf->y; i > 0; i--) {
            to[0] = to[1] = to[2] = from[0];
            to[3] = 0xff;
            to += 4;
            from++;
          }
          break;
      }
    }

    if (flags & IB_metadata) {
      png_text *text_chunks;
      int count = png_get_text(png_ptr, info_ptr, &text_chunks, NULL);
      IMB_metadata_ensure(&ibuf->metadata);
      for (int i = 0; i < count; i++) {
        IMB_metadata_set_field(ibuf->metadata, text_chunks[i].key, text_chunks[i].text);
        ibuf->flags |= IB_metadata;
      }
    }

    png_read_end(png_ptr, info_ptr);
  }

  /* clean up */
  if (pixels) {
    MEM_freeN(pixels);
  }
  if (pixels16) {
    MEM_freeN(pixels16);
  }
  if (row_pointers) {
    MEM_freeN(row_pointers);
  }
  png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);

  return ibuf;
}