No colorspace information after opj_read_header

[HGuillemet]

image->color_space and image->icc_profile* are only filled in opj_decode() and not in opj_read_header(). This is problematic in situations where the color space must be know before decoding pixel data.

This should be easily fixable by moving from opj_jp2_decode() to opj_jp2_read_header() most of the code that copies color information from the jp2 struct to the image struct.

[lrosenth]

Indeed, this is necessary. I have cases where I need the color space information before decoding the image.

[sebras]

I recently discovered the same. Only after calling opj_decode() is opj_image_t->color_space set. Others have been asking for the same.

Would you accept patches to try to move the colorspace detection code to some function called by opj_read_header()? Maybe there is a reason for why the colorspace is not available until after image decoding?

[mara004]

@ OpenJPEG developers: any comments on this issue?
PDFium's FPDFImageObj_GetImageMetadata() function is affected by this problem, too.

[rouault]

attempt fix in #1463 . I'd appreciate if reporters could test that it actually fixes the issue (I'm not sure openjpeg test suite tests that)

[rouault]

@mara004 Did you have a chance to test #1463 ?

[mara004]

@rouault Unfortunately no, as I'm not using openjpeg directly, but only through pdfium, which bundles openjpeg.
However, I think pdfium may benefit from the change once they update their copy of openjpeg.

Apart from that, could you add a test case to confirm your implementation works?

[sebras]

@rouault I did a little investigation. I think changed so that one can access normal colorspaces after calling opj_read_header(), but not ICC profiles (they still require a call to opj_decode()). So unfortunately I think you only adressed half the bug.

As I understand it file1.jp2 from your testsuite sets sRGB in its COLR box. And now after your commit I see that ->color_space is set to OPJ_CLRSPC_SRGB immediately after the call to opj_read_header(), i.e. no need to call opj_decode() to determine the colorspace.

As for ICC profiles relax.jp2 appears to set an ICC profile in its COLR box and after the call to opj_read_header() then ->icc_profile_len and ->icc_profile_buf are not set. However after I have called opj_decode() both will be populated and I can retrieve and analyze the colorspace.

[rouault]

pull request amended to move ICC profile setting to image in read_header()

[sebras]

@rouault Thank you for fixing this! :)