PNG Image

[Twey]

John's right: sorry I took so long to reply, it's a nightmare to find information on this, and the standard is exceptionally unreadable.

PNG-8 is interesting for the old IEs, but I don't see much point these days. Images should, of course, not be vital for accessibility anyway, since some people can't use them at all, so all using PNG-8 will do is add a very thin layer of fallback between two existing ones, at the cost of limiting image quality.

[techno_race]

Usually, if it has tansparency and/or fore than 256 colors, I'll use PNG. Otherwise, I use GIF. (GIF's transparecy is 0/100, while PNG's is 0-100.)

[Twey]

Well, that's (one of) the point(s). In all the situations where GIF seems appropriate, barring animation, you should be using PNG: it compresses far better, if nothing else.

[jscheuer1]

Well, that's (one of) the point(s). In all the situations where GIF seems appropriate, barring animation, you should be using PNG: it compresses far better, if nothing else.

Not always, but yes usually. With extremely simple and small things, .gif can still be better.

[Twey]

Oh, you seem to be right. It would be interesting to see exactly where they broke even. I'm guessing that the PNG is larger because of the extra meta-data?

[jscheuer1]

Well, I was thinking. You can use a utility like pngcrush to strip out all or most of the non-essential chunks. At that point .png might be better or the same. But the extra effort (unless pngcrush code could be implemented into your default image editor) makes it pointless.

I do use pngcrush though for png images that are already smaller than the .gif - to get them even smaller, and sometimes to correct (remove) the gamma chunk for IE.

[Twey]

The GIMP's compression routine includes features equivalent to (at least the non-destructive of) pngcrush, and allows one to decline to save gamma information when making a PNG image. I used the GIMP and found that a solid white 4px×4px image as a GIF was roughly ⅓ the size of the equivalent PNG: 36 bytes compared to 98. Perhaps pngcrush can get it smaller, but I would be fairly surprised.

[jscheuer1]

I may try your 4 x 4 solid white idea in pngcrush. It has a switch setting:

pngcrush -rem alla

That takes away everything possible. I think it would ruin complex images, but with a simple image like we are talking about, it would be fine.

I seem to remember doing similar trials at one point though, and .gif was still smaller.

[jscheuer1]

I got 37 bytes .gif, 83 bytes .png on my 4x4 solid white image. Using pngcrush provided no further optimization over my image editors (Paint Shop and Optimizer Pro).

[Twey]

I guess that's proven then. Not that sixty bytes are worth bothering with. It would be interesting if proportional differences were seen with larger and more complicated images... I wonder where the boundary is exactly?