Will saving a JPG as a Gif make it into a smaller file size?

yes it will

you may lose quality though

Not necessarily, it might actually increase the file size instead.

For smooth colour transitions, you typically want to avoid gif, but the best thing to do is experiment yourself.

Right, it depends on the image.

how about PNG?i dunno exactly, but for small picture,it will make smaller size.

the generic rule of thumb is when using photo-type images (portraits for example) with many DIFFERENT pixels, you should use jpg. using gif will reduce your filesize when fewer different pixels are used (logos and other vector images for example)

the difference comes in the way that gif and jpg handle compressions. gif uses a 'binary'-type compression. it essentially 'switches' pixels on and off, so the more diversity in the pixels, the more pixels it much switch on and off, hence a larger filesize. whereas jpg will handle this compression differently and result in a smaller filesize.

some excellent articles on gif vs jpg:

http://www.wfu.edu/~matthews/misc/jp.../JpgVsGif.html
http://hotwired.lycos.com/webmonkey/...html?tw=design
http://www.siriusweb.com/tutorials/gifvsjpg/

PNG is an up and coming web technology sure to take off, but IE's support for transparency seriously limits it's usability at this point.

That's correct.

Simply, use GIFs for unvaried, small number of coloured (excuse the apalling English there) images, and JPEGs for more varied images, like photographs.

I wouldn't touch PNG with a barge-pole unless necessary, as the filesizes tend to be, well, massive...

Originally Posted by Harvey

That's correct.

Simply, use GIFs for unvaried, small number of coloured (excuse the apalling English there) images, and JPEGs for more varied images, like photographs.

I wouldn't touch PNG with a barge-pole unless necessary, as the filesizes tend to be, well, massive...

exactly. this man is right!

You can use 8-bit alpha PNGs in IE 6 with a bit of judicious CSS...

I don't notice huge filesizes with my PNGs. Any other reason why I shouldn't be saving all my banners, logos, etc as png..?

You can't animate PNGs and some browsers don't support PNG transparency.

Okay, I don't do animations for one.
And, which browsers don't support PNG transparency and what do they do instead?

Yes, I don't often animate gifs either. IE doesn't support transparency though it's rumoured that version 7 will.

Originally Posted by Me

You can use 8-bit alpha PNGs in IE 6 with a bit of judicious CSS...

Look at www.rmf33.co.uk in IE and you'll see I have transparent pngs scattered all over with no trouble.

There I was thinking I'd have to wait for IE7 and you've already gone and done it.

Maybe IE7 will support background-attachment: fixed!

EDIT: I'm confused! I read 'everywhere' that IE doesn't support alpha channel transparency, yet you appear to have shown the opposite. Oberon, can you shed any light on what you can and can't do with pngs and IE?

Originally Posted by gringo

Maybe IE7 will support background-attachment: fixed!

Ah yes, that's one thing IE 6 won't do properly as of yet.

For transparent pngs my CSS goes like this:

#nbg { 
       filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(enabled=true, sizingMethod='scale', src='images/fuzzm.png');
       background-repeat: repeat-y;
       width:231px;
}

fuzzm.png is a semitransparent graphic a few pixels high that fades at the edges to totally transparent. It makes the main column of my navigation menu. You can also use 'crop' as the sizing method instead of scale.

This all lives in an IE specific stylesheet. I include a different one in the page depending on what browser you look at the page with.

I was looking at the stylesheet presented to firefox and would never have known there was an ie specific one!

Very clever. Thanks for that Oberon.