[Octave-bug-tracker] [bug #41584] .bmp / .png display error for saturated RGB image.

[Valery]

Follow-up Comment #5, bug #41584 (project octave):

Hi, 

the problem shows up to me when using the following images:

PNG 1250x1250 1250x1250+0+0 8-bit sRGB 250KB 0.000u 0:00.000

in which:

[...]
Colorspace: sRGB
  Depth: 8-bit
  Channel depth:
    red: 1-bit
    green: 8-bit
    blue: 8-bit
[...]

So the "unlucky" red channel causes get_depth currently to override the
correct default result value "8" with the incorrect "1", what then leads to
the false matrix type "logical".

As quick-n-dirty fix I added these two lines with conditions for the green and
blue channels:

libinterp/dldfcn/__magick_read__.cc

static octave_idx_type
get_depth (Magick::Image& img)
{
  octave_idx_type depth = img.depth ();
  if (depth == 8
      && img.channelDepth (Magick::RedChannel)     == 1
      && img.channelDepth (Magick::GreenChannel)   == 1 // <<--- added
      && img.channelDepth (Magick::BlueChannel)    == 1 // <<--- added
      && img.channelDepth (Magick::CyanChannel)    == 1
      && img.channelDepth (Magick::OpacityChannel) == 1
      && img.channelDepth (Magick::GrayChannel)    == 1)
    depth = 1;

  return depth;
}

and am getting uint8 for the image matrix in result.
Now I am bound to this my fixed Octave version and would be cool if this or
other patch could be incorporated in next public releases.

P.S. Disclaimer: I don't have an answer though, why Cyan, Opacity and Gray
channels all return depth of 1 for such images .



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