Greyscale JPEGs

taob · Post by **taob** » Sat Apr 05, 2003 2:38 pm

I'm running NeatImage 2.3 Pro, and it does not seem to be able to open greyscale (8-bit) JPEGs. Is anyone else seeing this problem? Here is a sample file you can try:

http://www.risc.org/Images/0404-205014-grey.jpg

Post by **NITeam** » Sat Apr 05, 2003 4:11 pm

Must be something with the format of grayscale JPEGs saved by GIMP.. Once this file is resaved in an image editor, it is easily opened by NI.

taob · Post by **taob** » Sun Apr 06, 2003 3:06 pm

That's not a very good solution though, you must admit.

Every other image program I've tried (GIMP, ImageMagick, xv, gqview, eog, Photoshop, ACDSee, ThumbsPlus, Qimage Pro, Canon ZoomBrowser, Canon PhotoStich, etc., etc.) don't have a problem opening those greyscale images. Perhaps the JPEG decode routine in NeatImage assumes that there must be exactly three, direct-mapped RGB channels in every JPEG (as opposed to possible a single channel LUT)?

I don't know if this helps you, but ImageMagick's "identify" command says this about a full colour and a greyscale JPEG:

Code: Select all

colour.jpg JPEG 3086x2054+0+0 DirectClass 8-bit 11.8m 0.000u 0:01
greyscale.jpg JPEG 3086x2054+0+0 PseudoClass 256c 8-bit 8.1m 0.000u 0:01

Post by **NITeam** » Sun Apr 06, 2003 4:25 pm

I was not proposing a solution through rewriting. I just wanted to indicate that it was quite possible that the whole issue could be resolved before images gets to NI.

Yes, NI does only accept grayscale JPEGs with the channel values directly-mapped to Y space. Anything else like LUT is not supported. I believe there is no any real need for this anyway. - Most applications save grayscale JPEGs without LUT, which is confirmed by the earlier test with rewriting the image in an editor.

So, to resolve the problem you can just save such JPEGs in GIMP into 'normal' grayscale JPEG format, without any LUTs. Especially since they utilize all 256 levels of gray.