Reducing File Size for PNG Images

[ReX]

I realize that file size has become much less of an issue in recent years because of larger bandwidth and faster download speeds. Still, one thing that has bothered me about PNG format images is that they tend to have large file sizes. Collectively, they can make files quite large (and, at some point, make the pk3 or wad take longer to load at game start). At any rate, I was poking around and came across an on-line tool named TinyPNG where I was able to reduce PNG image file sizes by around 70% or more.

The free version allows you to compress up to 20 files, with a maximum file size of 5 MB each. At present, the only way I have found to compress more than 20 files is to exit the web-site, re-enter it, and then drop the next 20 images into the tool. The speed with which the compression occurs is fairly high, and the compressed images are virtually indistinguishable from the originals. So I am very satisfied with the process and the results.

[EDIT: I didn't realize that there have been other posts about this topic.]

[Rachael]

I really would not use an online utility for it, especially not for Doom resources.

The best utility to use is pngout. Make sure to run it with "/kgrAb"

After that, you can run deflopt (with /k) to further reduce its size by a few more bytes.

Unfortunately, the original site for deflopt has expired. It appears you can get it with PNGGauntlet, though.

[ReX]

I really would not use an online utility for it, especially not for Doom resources.

I'm not quite sure what your objection is based on. I just ran it for 83 files and it was reasonably quick and the results were, for all intents and purposes, lossless.

The best utility to use is pngout. Make sure to run it with "/kgrAb"

I will give this utility a try too, thanks.

[Rachael]

I really would not use an online utility for it, especially not for Doom resources.

I'm not quite sure what your objection is based on. I just ran it for 83 files and it was reasonably quick and the results were, for all intents and purposes, lossless.

You'll lose the grAb and alPh chunks - which is vital information for GZDoom resources. grAb is for sprite offsets and alPh holds alpha information.

[Graf Zahl]

alPh is obsolete. It was once used for alpha textures in the software renderer, but that has been refactored so that it isn't needed anymore. The hardware renderer never even used it - it was just a crutch to patch over some shortcomings in the texture manager.

[Matt]

Is there any way to edit the grAb chunk without grabPNG or some other program made specifically to deal with it?

[Rachael]

Hex editor?

I don't think there's any reason to compress data that small.

That being said, SLADE handles them perfectly, also.

[ReX]

You'll lose the grAb and alPh chunks - which is vital information for GZDoom resources. grAb is for sprite offsets .....

Good to know, thanks.

[Kappes Buur]

Another vote for Slade3's png optimization

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filesizes before optimization

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filesizes after optimization

[Graf Zahl]

Hex editor?

That may throw off third party PNG tools because the chunk's CRC will no longer match. I know for sure that some tools will not handle this gracefully and start spamming error messages.

[Rachael]

Oh, I forgot about the CRC. I think when I did it I manually updated the CRC myself.