problem with anaglyph resizing in ZenPhoto for stereoscopic gallery

dromeuf

Hello,

I would like to use ZenPhoto to make a stereoscopic gallery with red/cyan anaglyph. I have a big problem with ZenPhoto and anaglyphs because the resizing process disrupts vision, introduce ghosts in the image. In fact Anaglyph resized by ZenPhoto change the colors (my pictures are sRGB profile). This problem is just like when transformed an anaglyph to CMYK for offset printing for example. The resizing process convert to CMYK (JPEG sRGB to CMYK) ??? resizing process change the color space of the JPG file ???

For example this anaglyph resized by ZenPhoto :
http://www.david-romeuf.fr/albums/index.php?album=archeologie-arverne-a-corent&image=dromeuf-anag-033-corentfouillesarcheocavetaverne-l1280.jpg
There are ghosts on amphores, the depth is not good. Object disturbing stereo vision. the resizing version is bad.

and the original source file :
http://www.stereauvergne.fr/3D/Anaglyphes/FouillesArcheoCorent/DRomeuf-anag-033-CorentFouillesArcheoCaveTaverne-l1280.jpg
with no ghosting effect, perfect left/right separation.

I have write this paper for the offset CMYK anaglyphe printing problem :
http://www.david-romeuf.fr/3D/Anaglyphes/RetourExperienceImpressionAnaglyphe/AnaglyphsPrintingExperienceFeedback.html

Do you have any solution for ZenPhoto resizing process not modify colors ?

Thanks for advance, David.

acrylian

Sorry, both look fine and the same to me in Safari 4 and the stereoscopic effect works fine, too. (You know Firefox and Safari are the only browsers to support color profiles.)

That the conversion from RGB to CMYK changes the colors is normal as CMYK has naturally a smaller color range than RGB. Anyway, color management is a difficult topic but sRGB should actually be fine for the web.

If I remember correctly the GD libary (installed on your server) that is used to process the images does not care for color profiles at all. Nothing we can't do anything against that.

The fix would be to resize images to the size they are displayed on the site so they do not need to be resized.

dromeuf

Yes acrylian, CMYK color space is smaller than sRGB (it' in my webpage), but I dont't understand why a resizing process from sRGB to sRGB modify so much the colors.
On windows XP with Firefox 3, I have the same problem. There are ghosts (color crosstalk) on amphora.

The evidence is that the original source image look well in IE or Firefox (resized by the by functionnality of the navigator or full frame) :
http://www.stereauvergne.fr/3D/Anaglyphes/FouillesArcheoCorent/DRomeuf-anag-033-CorentFouillesArcheoCaveTaverne-l1280.jpg

But not the resizing ZenPhoto version.

Best regards, David.

acrylian

Well, I just looked at both images with Photoshop and honestly I don't see a real difference. Maybe I have tomatoes on my eyes but I see no ghosts (except those shifted color for the stereoscopic effect). Do you mean that line on the green color on the broken ampore in the foreground? You might need to experiment a little with the sharping and compression level options on the backend options.

Also note both images are not sRGB there is no color profile attached. Just RGB at least PS tells.

You might also search the web on the GDlibary whose functionality is out of our hands.

EDIT: You might also search the forum a little, we had a discussion about color management some time ago.

dromeuf

Hi Acrylian,

I found a solution : In fact, the problem is with JPG image file. When you upload PNG image file this problem does not occur. With PNG images files, resizing process and watermarked process work fine.

You can see the difference between PNG and JPG source file :

PNG sRGB source file : http://www.david-romeuf.fr/albums/index.php?album=archeologie-arverne-a-corent&image=dromeuf-anag-033-corentfouillesarcheocavetaverne_1280.png

JPG sRGB source file (very BAD result on amphora) : http://www.david-romeuf.fr/albums/index.php?album=archeologie-arverne-a-corent&image=dromeuf-anag-033-corentfouillesarcheocavetaverne-l1280.jpg

It's ok for me with anaglyph PNG file and ZenPhoto.

David.

acrylian

Great, you got it to work. The reason is probably that PNGs, especially the PNG24 ones, are not lossy compressed as JPEGs are. I see the difference but you really need to know what your are looking for..;-)