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PNG images are going to be large. If there is a lot of detail, they are going to be larger. Big areas of solid color reduce file size. Alpha channels add additional file size because there is an additional color channel with up to Trillions of colors. 8-Bit PNG files are smaller but you lose a lot of color information. There are no different compression options for PNG files that will significantly change the file size.
Take a look at the difference between these two reports on 10 PNG images rendered in a sequence from After Effects:
That is 10 HD frames of this desert scene and it's 108.2 MB
The second is 10 frames of an HD blue solid moving halfway across the frame with an alpha channel and no motion blur. It's only 189 KB.
This is what happens to the file size when you turn on Motion Blur. Just that tiny bit of transparency from the motion blur added 3 KB in 10 frames. Imagine how much larger a file of an actor with long blond hair blowing in the wind that was expertly keyed out in AE could be, just from the complex alpha channel date.
With frames that look like this:
If you want visually lossless files that are 10-bit or better, you're stuck with large file sizes. Other image formats can give you a little smaller file sizes and retain high quality, but the difference is not going to allow you to store twice as much footage on your drives and the render time may outweigh the little money you would save buying more storage. GoPro Cineform supports alpha channels and 10-bit color and the file sizes are about as small as you can get for this kind of project. Here's what a 10 frame render of the desert scene looks like using Cineform and it renders in about half the time as a PNG sequence.
So Cineform is less than half the file size and renders in less than half the time but it is only a 10-bit movie but it does include an Alpha channel. PNG files can be 16 bit. You'll need TIFF or other image formats if you want 32.
I don't know for sure but it looks like Blink video converter (compressor) would handle GoPro Cineform without any problems and you could include audio. It looks like a lot better solution to me.
One more thing. Any PNG compressor that reduces file size will compress the colors. Your 16-bit originals will be compressed all the way down to 8 bits or even less if you use any of those tools. There is no way around the architecture without compressing colors. That is why the animated blue solid file size is so small. If I just applied 4 color gradient to the solid the file size would jump up dramatically.
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