Function lodepng_convert

src/lodepng.cpp:3393–3458

converts from any color type to 24-bit or 32-bit (later maybe more supported). return value = LodePNG error code the out buffer must have (w * h * bpp + 7) / 8 bytes, where bpp is the bits per pixel of the output color type (lodepng_get_bpp) for < 8 bpp images, there may _not_ be padding bits at the end of scanlines. */

(lodepng_get_bpp) for < 8 bpp images, there may _not_ be padding bits at the end of scanlines.
*/
unsigned lodepng_convert(unsigned char* out, const unsigned char* in,
                         LodePNGColorMode* mode_out, const LodePNGColorMode* mode_in,
                         unsigned w, unsigned h, unsigned fix_png)
{
  unsigned error = 0;
  size_t i;
  ColorTree tree;
  size_t numpixels = w * h;

  if(lodepng_color_mode_equal(mode_out, mode_in))
  {
    size_t numbytes = lodepng_get_raw_size(w, h, mode_in);
    for(i = 0; i < numbytes; i++) out[i] = in[i];
    return error;
  }

  if(mode_out->colortype == LCT_PALETTE)
  {
    size_t palsize = 1 << mode_out->bitdepth;
    if(mode_out->palettesize < palsize) palsize = mode_out->palettesize;
    color_tree_init(&tree);
    for(i = 0; i < palsize; i++)
    {
      unsigned char* p = &mode_out->palette[i * 4];
      color_tree_add(&tree, p[0], p[1], p[2], p[3], i);
    }
  }

  if(mode_in->bitdepth == 16 && mode_out->bitdepth == 16)
  {
    for(i = 0; i < numpixels; i++)
    {
      unsigned short r = 0, g = 0, b = 0, a = 0;
      error = getPixelColorRGBA16(&r, &g, &b, &a, in, i, mode_in);
      if(error) break;
      error = rgba16ToPixel(out, i, mode_out, r, g, b, a);
      if(error) break;
    }
  }
  else if(mode_out->bitdepth == 8 && mode_out->colortype == LCT_RGBA)
  {
    error = getPixelColorsRGBA8(out, numpixels, 1, in, mode_in, fix_png);
  }
  else if(mode_out->bitdepth == 8 && mode_out->colortype == LCT_RGB)
  {
    error = getPixelColorsRGBA8(out, numpixels, 0, in, mode_in, fix_png);
  }
  else
  {
    unsigned char r = 0, g = 0, b = 0, a = 0;
    for(i = 0; i < numpixels; i++)
    {
      error = getPixelColorRGBA8(&r, &g, &b, &a, in, i, mode_in, fix_png);
      if(error) break;
      error = rgba8ToPixel(out, i, mode_out, &tree, r, g, b, a);
      if(error) break;
    }
  }