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My web image @ 16-bit is blech!

Posted: Sun May 15, 2005 8:01 am
by GillyH

Brand new Dell WinXp pc
Dell 17" CRT monitor (15.9 v.i.s.0.28 dot pitch)
30-day trial of Photoshop CS2

I've taken a manip image I made @ 439 px x 337 px

and incrementally resized it in increments of 10% upto 613 px x 471px for (I hoped) the centre of a wallpaper. Then I've used an action called De-colour by Lil Flame (duplicate current layer, duplicate current layer, grain, gaussian blur, set current layer, desaturate, merge layers, brightness/contrast, flatten image).

All looks as okay as I think it can be in Photoshop CS2. I save the file as a *.jpg and upload it to my webspace to check it. It looks okay at a screen res of 1024 x 768 and 800 x 600 and in a colour quality Highest (32 bit) in my display properties. But if I look at it at the same res(es) in a colour quality Medium (16 bit) it gets wavy, patchy lines of distorted colour on it and looks blech!

Thinking it was the De-colour action, I tried uploading a version where the action hadn't been applied, and I get the same thing.

So, any ideas? Granted, the pic quality is poor to begin with but is there an action or a filter that will help it look okay at 16-bit?



Posted: Sun May 15, 2005 12:56 pm
by mehdi
it's normal to see problems with 16 bits modes ...
you'll see problem with any picture that contains smooth gradients.
16 bits modes is a poor mode. The only reason to use this mode is if you have a very slow PC (pentium II with a crappy graphic card) .
All problems disappears wit 24bits and 32 bits modes.
Notice: 24 bits is the slowest mode, 32 bit the fastest.
Some people believes that 16bits is faster than 32bits , that's not true.
You may not use 32bits if your graphic card doesn't support this mode (crappy graphic card, again)

Posted: Mon May 16, 2005 8:27 am
by GillyH
Thanks, Mehdi. I thought it might be one of those things I just have to live with, but I hoped someone had made a filter or something to help. Oh, well. Back to the drawing board :)


Posted: Mon May 16, 2005 1:56 pm
by HaraldHeim
If you convert a 24bit image to a 16bit image, you need to apply some dithering to hide the decrease in quality. The free 5_6_5 plugin does that. You can get it from

Posted: Mon May 16, 2005 3:55 pm
by GillyH
^^Thanks very much, Harald. That plugin really helped! :D