问题
Our graphic artist is delivering image ready for print in CMYK colorspace JPG format, which is correct for printing. I am converting these for display on the web. I understand the "best" thing to do is convert the src.jpg to sRGB colorspace. I've tried both command line using convert and Imagick approach using transformImageColorspace() and find it works fine on my local machine (Fedora 32 Linux) but doesn't work on the production server (CentOS 7.3 Linux).
We've had this process working for a couple of years on production using the command line convert but we recently tightened security and disabled exec from PHP, so I'm trying to make the same process work via the Imagick bindings, but the resultant image doesn't display correctly. I don't know if the ICC color profile isn't being applied properly, or the conversion to sRGB is going wrong, or whatever else may be happening.
Local machine: Version: ImageMagick 6.9.10-86 Q16 x86_64 2020-01-31 https://imagemagick.org
Prod server: Version: ImageMagick 6.9.11-19 Q16 x86_64 2020-06-15 https://imagemagick.org
Both machines show 'lcms' is in the Delegates (built-in) list, which is one thing that may cause trouble but looks fine.
Source image: src.jpg in CMYK format, a mostly grey/white image.
Loading this image in Gnome's Image Viewer shows incorrect colours, a blueish tinge, but I think this is because Gnome doesn't handle the CMYK properly. Loading the same image into GIMP auto-converts it to sRGB and it shows grey/white properly. My aim is to produce output file src_srgb.jpg that displays grey/white when loaded in Image Viewer (so it clearly is a simple RGB profile image).
Source code:
class Logger {
public function log ($str) {
echo $str . "\n";
}
}
$l = new Logger();
$master_filename_abs = 'srgb/src.jpg';
$icc_profile_file = 'AdobeRGB1998.icc';
$pathinfo = pathinfo($master_filename_abs);
// e.g. turn mickey.jpg into mickey_srgb.jpg
$preview_filename = $pathinfo['filename'] . '_srgb.' . $pathinfo['extension'];
$preview_filename_abs = $pathinfo['dirname'] . '/' . $preview_filename;
$useCmdLine = false; // use cmd line 'convert', or Imagick?
try {
if ($useCmdLine) {
$cmd = 'convert "' . $master_filename_abs . '" -verbose' .
' -profile "' . $icc_profile_file . '"' .
' -colorspace srgb' .
' -resize 800 "' . $preview_filename_abs . '" 2>&1';
$l->log('executing "' . $cmd . '"...');
exec($cmd, $output, $return_var);
$l->log("exec returned $return_var with " . count($output) . ' lines of output:' .
join("\n", $output));
} else {
$master_img = new Imagick();
$master_img->readImage($master_filename_abs);
$icc_profile_contents = file_get_contents($icc_profile_file);
$l->log('About to profileImage()...');
$r = $master_img->profileImage('icc', $icc_profile_contents);
$l->log("profileImage returned $r " . ($r == TRUE ? 'true' : 'false'));
$space = $master_img->getImageColorspace();
$l->log("Colorspace starts as $space, CMYK is " . Imagick::COLORSPACE_CMYK);
$r = $master_img->transformImageColorspace(imagick::COLORSPACE_SRGB);
$l->log("transformImageColorspace returned $r " . ($r == TRUE ? 'true' : 'false'));
$space = $master_img->getImageColorspace();
$l->log("Colorspace after conversion is $space, SRGB is " . Imagick::COLORSPACE_SRGB);
$master_img->scaleImage(800, 0);
$l->log('Saving RGB profile version to ' . $preview_filename_abs);
$master_img->writeImage($preview_filename_abs);
}
} catch (Exception $ex) {
$l->log('Caught ' . $ex);
}
Prerequisites: the src.jpg should be in 'srgb' directory, and AdobeRGB1998.icc profile should be in current directory.
As you can see there's both the command line attempt, and the Imagick attempt, in the script, with a $useCmdLine boolean that toggles between them.
Result on local machine: src_srgb.jpg is created and looks OK. Colours match the src.jpg image.
$ /opt/remi/php71/root/bin/php imagick_srgb.php About to profileImage()... profileImage returned 1 true Colorspace starts as 13, CMYK is 12 transformImageColorspace returned 1 true Colorspace after conversion is 13, SRGB is 13 Saving RGB profile version to srgb/src_srgb.jpg
identify -verbose srgb/src_srgb.jpg shows:
Colorspace: sRGB
Type: TrueColor
...
Profiles:
Profile-8bim: 6694 bytes
Profile-exif: 4617 bytes
Profile-icc: 560 bytes
Profile-iptc: 17 bytes
unknown[2,0]:
Image Name[2,5]: Print
Profile-xmp: 16695 bytes
Result on prod server: src_srgb.jpg is created but looks blueish.
$ /opt/cpanel/ea-php73/root/usr/bin/php imagick_srgb.php
About to profileImage() with 1 bytes of profile data...
profileImage returned 1 true
Colorspace starts as 12, CMYK is 12
transformImageColorspace returned 1 true
Colorspace after conversion is 13, SRGB is 13
Saving RGB profile version to srgb/src_srgb.jpg
identify -verbose srgb/src_srgb.jpg shows:
Colorspace: sRGB
Type: TrueColor
...
Profiles:
Profile-8bim: 6694 bytes
Profile-exif: 4617 bytes
Profile-iptc: 17 bytes
unknown[2,0]:
Image Name[2,5]: Print
Profile-xmp: 16695 bytes
I see the 'good' version on local machine has Profile-icc in the list of profiles, whereas the 'bad' version from prod does not. Could this be connected to the root cause of the problem, and if so, what can I do about it? I believe exif, iptc and xmp profiles are metadata and can be safely ignored for the purpose of this test.
From a little trial and error I think I've got the transformImageColorspace and profileImage calls in the right order.
Advice would be hugely appreciated.
I cannot share the full src.jpg but here is a cropped part of it (cropped with imagemagick convert to retain its colour profile etc)
Edit Reading PHP Imagick won't add ICC color profile I thought I'd demonstrate production server's lcms presence:
$ convert -list configure | grep DELEGATES
DELEGATES bzlib djvu mpeg fftw fontconfig freetype gslib heic jbig jng jpeg lcms lzma openexr openjp2 pango png raqm raw rsvg tiff webp wmf x xml zlib zstd
DELEGATES bzlib cairo djvu fftw fontconfig freetype gslib gvc heic jbig jng jp2 jpeg lcms ltdl lzma openexr pangocairo png ps raqm raw rsvg tiff webp wmf x xml zlib
$ rpm -qa | grep cms
lcms2-devel-2.6-3.el7.x86_64
lcms2-2.6-3.el7.x86_64
Edit 2 There is something weird about imagemagick on the two systems. My local machine reports an icc profile on src.jpg, but production does not, for exactly the same image. I tried downloading my own attachment to this post as SO.jpg to check, copied it to prod, and diffed the output of identify -verbose SO.jpg:
$ diff so_local so_prod
1c1,2
< Image: SO.jpg
---
> Image:
> Filename: srgb/SO.jpg
12c13
< Endianess: Undefined
---
> Endianness: Undefined
83,84d83
< Profiles:
< Profile-icc: 557168 bytes
86,89c85,86
< date:create: 2020-06-17T06:14:10+00:00
< date:modify: 2020-06-17T06:14:10+00:00
< icc:copyright: Copyright 2000 Adobe Systems, Inc.
< icc:description: U.S. Web Coated (SWOP) v2
---
> date:create: 2020-06-17T06:14:59+00:00
> date:modify: 2020-06-17T06:14:59+00:00
94c91
< filename: SO.jpg
---
> filename: srgb/SO.jpg
99c96
< Pixels per second: 25.3889MB
---
> Pixels per second: 27.3785MB
102c99
< Version: ImageMagick 6.9.10-86 Q16 x86_64 2020-01-31 https://imagemagick.org
---
> Version: ImageMagick 6.9.11-19 Q16 x86_64 2020-06-15 https://imagemagick.org
This really stinks for me, with little understanding of imagemagick. I will look into downgrading ImageMagick packages on production to match local but we're getting into daytime operating hours on a production server so I may not be able to.
Edit 3 Going back over our historical jobs, it seems to have stopped working on June 1 2020, and on that day I see that ImageMagick-6.9.11.14-1.el7.remi.x86_64 was upgraded to ImageMagick-6.9.11.16-1.el7.remi.x86_64 (and the -libs and -devel packages too). So, it looks like this breaking change was introduced between 6.9.11.14-1 and 6.9.11.16-1. The remi repo we get them from only seems to hold two most recent, 6.9.11.18-1 and 6.9.11.19-1 and downgrading to 6.9.11.18-1 does not fix it for me.
Edit 4 May have got PHP Imagick bindings to do the conversion successfully. From a comment at https://www.imagemagick.org/discourse-server/viewtopic.php?p=67114#p67114 "you should define the colorspace CMYK before , apply whatever operation you need and then define the RGB colorspace" with the example convert -colorspace CMYK mona_lisa.cmyk.jpg -modulate 110 -colorspace RGB monalisa_rgb.jpg .. so I tried it in a desperate attempt (first setting profile to null to remove any existing ones):
$r = $master_img->profileImage('icc', null);
$r = $master_img->profileImage('icc', file_get_contents($cmyk_icc_profile_file));
$r = $master_img->profileImage('icc', file_get_contents($srgb_icc_profile_file));
$r = $master_img->transformImageColorspace(imagick::COLORSPACE_SRGB);
To my great surprise, with my local version 6.9.10-86 and old version 6.9.11-14 on prod, the output file appears correct in Gnome Image Viewer and web browser, so I think that's one problem solved. I've still not figured out why the latest version of ImageMagick 6.9.11-19 doesn't seem to work, will keep at it.
来源：https://stackoverflow.com/questions/62421778/why-would-converting-cmyk-image-to-srgb-for-display-on-web-work-locally-but-not