PNG Compression Level

[johnt53984649]

I noticed in the Photoshop Scripting guide, PNGSaveOptions has a member called "compression", which takes an integer between 0 and 9, inclusive.

However, I am confused as to what this value corresponds to.  In the GUI, when saving a PNG, the only options are these:

I'm not sure how a value between 0 and 9 corresponds to "None/Fast" or "Smallest / Slow".

Can somebody please explain what each of the 0-9 compression levels correspond to, or how they work?  I would appreciate some background.  Thanks.

[r-bin]

"None/Fast" -> compression=0

"Smallest/Slow" -> compression=9

[johnt53984649]

So then what's everything in between?  (1-8)?

[johnt53984649]

Does anybody know what the levels in between correspond to?  I have still been unable to locate this information.

[JJMack]

Why not experiment on a set of documents measure the differences in sized between sizes for each image save are all the compression levels. To get some idea the ranges,  Size differences will most likely be effected by the amount of detail in images so vary the amount of details in images.  You may also want to measure the amount of time leach level takes to compress the data. Time and space.

[johnt53984649]

Surely there's documentation on the compression algorithm Adobe is using somewhere!

[JJMack]

These are user forums. We do not work for Adobe. We do not have access to Phtoshop's code or internal Adobe documentation.  As far as I know PNG is not an Adobe image file format they can mess about with. Have you read up on Portable Network Graphics - Wikipedia