Convert does not preserve transparency

[ggeeoo]

Convert does not preserve transparency for some png files that I have. This only happens with the Q16 build. The Q8 works just fine. I had this issue with 6.4.0-9 under Linux and Windows. Here's one of the files that exemplify the problem. I used the following command:

Code: Select all

convert 1.png 2.png

[magick]

We tried your command with ImageMagick 6.4.0-10, the current release, at Q16 and the conversion went as expected (both images were identical).

[ggeeoo]

I tried 6.4.0-10 Q16 under Linux and Windows and had the same problem. It seems that the original image is problematic. I tried to open and then save it with several programs and it worked correctly (ie the transparency is preserved) with the exception of Photoshop and ImageMagick Q16. GIMP gave the following error message "Image resolution is out of bounds, using the default resolution instead" but rendered the image correctly.

[rmabry]

Same problem today, Windows 7, ImageMagick 6.6.7-0 2011-01-01 Q16. Using the image here,

http://www.maik-juergens.de/imagemagick/image1.png

I run

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convert image1.png image1-copy.png

and get a copy with no transparency.

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identify image1.png
image1.png PNG 46x48 46x48+0+0 8-bit DirectClass 538B 0.000u 0:00.000

identify image1-copy.png
image1-copy.png PNG 46x48 46x48+0+0 8-bit PseudoClass 49c 654B 0.000u 0:00.000

[glennrp]

It is working for me (IM-6.6.7-1, Q8 and Q16). The resulting images are indeed PseudoClass (paletted PNG, color-type 3), but they have a tRNS chunk to convey the transparency.

If you are using a viewer that cannot handle this type of image, then use

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convert image1.png PNG32:image1-copy.png

to force IM to write an RGBA PNG.

Pngcrush -n -v reports:

• Found tRNS chunk in input file.
  png_set_tRNS, num_trans=45
  Palette:
  I R G B ( color ) A
  0 255 255 255 (#ffffff) 0
  1 33 160 210 (#21a0d2) 14
  2 33 160 210 (#21a0d2) 83
  3 33 160 210 (#21a0d2) 144
  4 33 160 210 (#21a0d2) 194
  5 33 160 210 (#21a0d2) 232
  6 33 160 210 (#21a0d2) 253
  7 141 210 33 (#8dd221) 253
  8 141 210 33 (#8dd221) 232
  9 141 210 33 (#8dd221) 194
  10 141 210 33 (#8dd221) 144
  11 141 210 33 (#8dd221) 83
  12 141 210 33 (#8dd221) 14
  13 33 160 210 (#21a0d2) 94
  14 33 160 210 (#21a0d2) 185
  15 141 210 33 (#8dd221) 185
  16 141 210 33 (#8dd221) 94
  17 33 160 210 (#21a0d2) 29
  18 33 160 210 (#21a0d2) 142
  19 141 210 33 (#8dd221) 142
  20 141 210 33 (#8dd221) 29
  21 33 160 210 (#21a0d2) 158
  22 141 210 33 (#8dd221) 158
  23 210 54 33 (#d23621) 253
  24 210 146 33 (#d29221) 253
  25 210 54 33 (#d23621) 232
  26 210 146 33 (#d29221) 232
  27 210 54 33 (#d23621) 194
  28 210 146 33 (#d29221) 194
  29 210 54 33 (#d23621) 144
  30 210 146 33 (#d29221) 144
  31 210 54 33 (#d23621) 83
  32 210 146 33 (#d29221) 83
  33 210 54 33 (#d23621) 14
  34 210 54 33 (#d23621) 185
  35 210 146 33 (#d29221) 185
  36 210 146 33 (#d29221) 14
  37 210 54 33 (#d23621) 94
  38 210 146 33 (#d29221) 94
  39 210 54 33 (#d23621) 142
  40 210 146 33 (#d29221) 142
  41 210 54 33 (#d23621) 29
  42 210 54 33 (#d23621) 158
  43 210 146 33 (#d29221) 158
  44 210 146 33 (#d29221) 29
  45 33 160 210 (#21a0d2) 255
  46 141 210 33 (#8dd221) 255
  47 210 54 33 (#d23621) 255
  48 210 146 33 (#d29221) 255

Note that all but the last four colors in the palette have some degree of transparency.
If you look at the result of "identify -verbose image1.png | grep signature'
and repeat for the output image you will find that the signatures are the same.

[rmabry]

Hi Glenn,

Thanks, that works and solved related problems for me.

So (I address this to to one and all), another lesson here is that convert with no parameters should not be expected to act as a copy command. [Edit: I mean, of course, where the input and output formats match.] I have been under the opposite impression for quite a while. Is there then a set of default attributes that one should expect to be preserved? A set of attributes of a given format that is expected to be imposed? Is this somewhere writ?

Rick