Preserved Topic: Saving images for web pages?

I have a question that probably has a simple answer. I am trying to figure out how to save images effectively for webpages.

I usually make my page and it looks wonderful in 32bit color but then I remember 16bit color..switch my windows over and i have a ton of images that dont match up colors (i.e. where jpg and gif hit..)

How can I effectivley save my images to work in 16bit or 32bit, and still keep my image quality?

Thanks in Advance.

Well first of all, lets talk about gifs... there is no such thing as a 32bit gif, so however you save your gif, it should look fine in 8 bit color or higher.

Second, Jpegs... If you are using all 32bits of color (that's millions of colors) in a single jpeg, that's a huge file, so I doubt that is what you are doing. Chances are you are still only using 8 to 16 bits worth of color (that's 256 to thousands of colors).

What you are saying doesn't really make sense then, both the gifs and jpegs you are using should look fine at lower res (granted they may be missing a few colors, but not much).

And lastly, who is your target audience? I have never worried about the folks viewing my pages with only 8 bit color, because very very few people still use such a low resolution. Even folks with 2MB video ram (older legacy computers) can render thousands of colors at 800 X 600. And you have to think, if your audience is going to consist of these folks, then do you think they have a high speed modem to be downloading pictures with??? Probably not, so in that case you would want to use few pictures, and low res ones at that.

In light of this, maybe you can give us some more info, maybe even some examples.

-D

Thats not true... there are such things as 32 bit .gifs.. photoshop just has no way to save them. Sorry, nothing to add otherwise, I just figured that needed pointing out. LZW is the compression scheme used in tons of files and file formats, not just .gif... it can easily be manipulated to save a .gif file with over 256 colors.

Its a shame photoshop doesnt do it, actually. Maybe next time 'round.




A small mind is a tidy mind.

hes talking about monitor color resolutions.

i have images that degrade at 16 bit color as well. it usually has to do with gradients and the number of colors youre using. gradients will almost always cause "banding" at lower color settings. after all, you cant see 32 bit color if your monitor is set to only 16 bit.

for color matching, *always* stick with gifs. even pngs dont cut it. dont mix file formats if you want your colors to match exactly.

it might also be helpful if you keep your monitor set at 16 bit color while designing. you know it will look good in 32 bit, so concentrate on making it look good at 16 bit.

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Hell hath no fury like a woman scorned

Actually it depends on the type of image you're color matching. if it's something photorealistic, gif is decidedly not your best choice.

Your problem is the way JPGs work. You cannot control the exact colors that you will get when you output a JPG.

One of the optimizations that the JPG format uses involves shifting colors slightly. It tries to minimize the number of unique color entries (within a given 5x5 cell) by shifting similar colors to the same RGB value. So if you have FF88CC and FF8AC9 pixels throughout the cell, the conversion to JPG might convert them all to FF89CA. If you had designed your image so that the FF8AC9 pixels in the JPG perfectly aligned to some FF8AC9 pixels in an adjacent GIF, you'll notice a break where the GIF meets the FF89CA pixels in the JPG.

There is no easy way to correct for this. No application lets you 'lock' pixels in a JPG to a specific RGB value, so you have no control over what the exact RGB values will be when you convert to JPG. The problem is compounded by the way browsers display JPGs at different screen color depths. There are usually differences between the 16-bit and 32-bit versions, even if the original image had a limited color palette. The JPG conversion converts the image to 32-bit, then starts changeing RGB values willy-nilly, so you can actually end up with MORE unique colors in the final JPG than in the original RGB image.


There are a few workarounds:
- Use GIFs only. A 256 color 100% dither GIF can display fairly convincing photo-real images. They're not quite as good as JPGs, and are usually MUCH larger than the equivilent JPG.
- Don't design for invisible image boundries. Put a frame around JPGs, for example.
- Use very dark backgrounds. The "Asylum" logo in the upper left of the forum, for example, is a JPG with a dark blue background. If I switch my display down to 16-bit color, I can see the color break between the JPG and the background, but only if I look closely. The human eye has a harder time telling the difference between similar dark colors.

Thanks for all the comments.

Using a mixture of some .jpg and some .gif I was able to make everything match up in 8oox6oo and 1o24x768..so woo!

Feel free to check the site out also..hefty load time..but that's because all my images aren't compressed yet..Uhm..if you'd like to comment I posted in the site reviews forum here: http://www.ozoneasylum.com/Forum6/HTML/000352.html

Thanks.
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Doh..this is my sig for a RPG related Forum where I am an admin..hehe..I'm NOT an admin here =)

[This message has been edited by Shifter (edited 02-09-2001).]