PNG compression in Blender

symbiob · April 23, 2018, 7:47am

Hello!

If PNG compression is truly lossless, then one might as well have the compression of PNG output ramped right up to 100%, right? That would surely result in 100% compressed PNG images far smaller in file size, that look exactly the same as PNGs without any compression at all yet take up a lot more disk space, right?

Which begs the question; if 100% compressed PNGs, and PNGs without any compression look exactly the same, why does Blender even bother giving PNGs a compression option?

Photoshop’s PNG export does not give a compression option, probably because Adobe knows PNG compression is meaningless (and so P’shop can ONLY export PNG at max compression)… so why is Blender different?

Is there REALLY no disadvantage to 100% compressed PNGs?

organic · April 25, 2018, 7:19pm

I’m guessing read/write for highly compressed .png files will cause more cpu load and probably use more RAM. Could make a difference if there are a lot of them as every individual image must be decompressed. Uncompressed files will use more disc space but will process faster and use less resources.

If you are dealing with a long sequence you would prefer realtime playback in the VSE.

AIBlender · April 25, 2018, 7:19pm

What Organic said, having the png at 100% makes a massive difference in the time it takes for the png to be created and written to disk. It not big enough to notice if you are doing a single render. But if you are rendering a series of frames it is very noticable.

symbiob · April 25, 2018, 7:19pm

Aha, yes very good point, I hadn’t thought of that. That trade-off between file-size and speed makes sense. Many thanks.

Quantum_Anomaly · April 25, 2018, 7:19pm

So 100% PNG compression means the PNG is at maximum compression? I always thought 100% was full quality and anything less was lossy. But then PNG being a lossless format it always confused me that there was a compression option at all and I thought maybe the value slider was there regardless of what format you choose and it didn’t do anything for PNG. One of those things I wondered about but didn’t bother starting a thread over. Symbiob, glad you brought it up.