Legacy ImageMagick Discussions Archive

On my company's intranet site I'd like to allow the upload of the following file types which I'd then like to convert to JPEG and resize:

TIFF, GIF, PNG, EPS, PS, PDF

Although I can convert all these types my attempts have always resulted in colors differences between the original file and the new JPEG. Although some color difference is acceptable the difference I get are quite considerable.

I'd like to know if there's a "perfect" setup for ImageMagick. I have complete control over the server I use and would happily put on any Linux OS with any modules required but I'm not even sure if this perfect setup is possible in an entirely automated system. Should it be possible to convert for example from CMYK to RGB acceptably given any potential source of CMYK TIFF or PNG? Should it be possible to convert from all of the above formats to JPEG with excellent results with no manual intervention?

If anyone out there has the knowledge on how to do this but isn't inclined to post publicly then we are more than happy to pay for consultancy if you or someone you know is an ImageMagick wizz.

Many thanks from an increasingly desperate James.

I don't claim to be an expert, but some things you might consider.

First convert to something like RGB PNG or TIFF (uncompressed) to preserve color, then resize, then convert to JPG. JPG is a lossy compression and will change colors some, so make that the last step so that you don't compress twice (first to jpg, then to resize and compress again when making the output.)

Also if your input images are CMYK, you may need profiles to convert to RGB without loss of quality.

EPS, PS and PDF may require better or direct software using Ghostscript. I think I have seen some posts about the default Ghostscript delegate that IM uses is not the best means of doing this. Search the archives on these forums and see if you can find these comments. Here is one post:

viewtopic.php?f=1&t=10743&p=34088&hilit ... ipt#p34088

Thanks for the input. I'll give your suggestions regarding the two step conversion a go.

The subject of profiles confuses me. Could there be an unlimited number of profiles to account for or do you only need to worry about a key few? I read about using a standard CMYY.icm with a standard sRGB.icm but after giving it a go the colors were improved but still too far adjusted to be useful. Is this because I need to use the very same color profile for converting the image that was used to create it.

The Ghostscript link was to a topic I started

James
(off to wikipedia to read about color profiles)

Unfortunately the two step conversion didn't yield any improved results.

When I use color profiles, the results get a little better:

convert input.tif -strip -profile RSWOP.ICM -profile sRGB.icm output.png

The thing is, I have no clue which color profile I should be using and when. The sRGB.icm is a profile that was installed with ImageMagick on my Debian server. The RSWOP.ICM file is one I found on my Windows XP machine! So I wouldn't expect to get great results.

Does the color profile used to read the TIFF have to match the one that was used in the application that created it?

Has anyone found a perfect or near-ideal way of converting from TIFF to RGB? Is it even possible? I've been through loads and loads of posts and sites but with no definitive answer.

Thanks,

James.

James did you ever resolve this issue. I am currently experiencing the same thing.

Thank
Steve