Saving png files in Photoshop

[dkauha]

I've just upgraded to Photoshop CC 2019, and when I save a file to PNG (from the Save As dropdown menu), the Large file size format option creates a png with the same file size (in kb) as selecting the Smallest file size option. Selecting the Medium file size option produced the same result. In earlier versions of Photoshop, the Large file size option would create a high-resolution version that was significantly larger than the Smaller size option.

I opened the same project in an earlier version of Photoshop, did a Save As to a PNG file, selected Large file size, and sure enough, the png produced is much larger (in mb) than selecting the Small file size.

Is this a bug? Does anyone have this issue? And if so, are there any resolutions/workarounds I'm missing?

Thank you!

[gener7]

Well, I don't think anything is broken, just the way PNG compression works on the CC versions

Let's take a 900k jpeg:

CC2019 (I'm using a Macbook) L  4.3 MB  S 4.2 MB and a good long time to save it. Not much advantage  There really is a size difference, just not much.

Now lets go to CS6 Mac with the same jpeg:

Uncompressed  33.6 MB  S 4.3 MB  Bear in mind PNG compression isn't lossy like Jpeg. Jpeg throws out picture data to get those really small sizes, hence the term "Lossy compression."

33.6 MB is the file size in memory, and for the Large size is not the same as uncompressed, just compression that is fast but slightly larger than Small.

[johng9625402]

PNG is a lossless file format. So compression works much like if you zipped up the image. Images mostly are a type of file compression just re-translated when open. What this means is, is most likely you're not really going to get much more savings out of a compressed file.

I repeated your test with 2019 and went from 33meg file to 28meg png file.

As side test i zipped up a 33meg png file and got 28meg zip file

I also zipped up the compressed 28meg png file and and got a 28meg zip file

I found if I had a compressed file and opened it up and saved it as large it didn't return to 33meg it went to 29meg.

I then uncompressed all versions of my test file and did a MD5 tag on them and all versions were the same.

My guess is photoshop isn't uncompressing the file when saving to large which is why your not getting any file savings.

Not sure this would be considered a bug except for the fact the at some point the image needs to be uncompressed to be rendered on a screen.

[Abambo]

John-DDB  wrote

My guess is photoshop isn't uncompressing the file when saving to large which is why your not getting any file savings.

That’s a strange guess and does not make much sense.

[johng9625402]

Maybe i should of put the data in a bit of easier to understand format.

Original png	small file size	small file size resaved to large	ffmpeg uncompressed png
33,766,530 bytes	28,837,003 bytes	29,996,019 bytes	44,792,507 bytes
MD5=058f050474e6cf7637dc1b580eaafb93	MD5=058f050474e6cf7637dc1b580eaafb93	MD5=058f050474e6cf7637dc1b580eaafb93	MD5=058f050474e6cf7637dc1b580eaafb93

I uncompressed it in ffmpeg and got the MD5 tag. Shows the files are exactly the same when fully uncompressed so nothing is changing.

Like I said before I wouldn't really consider this a bug except that the uncompressing has to happen somewhere.

[gener7]

Uncompressing happens each and every time you open a file in Photoshop.

Out of curiosity, what size in bytes is Image Size giving you when you open any of the PNGs in Photoshop?

Also metadata (file information) plays a part. One of my pngs has 2 MB of such added to 3.6 increasing the uncompressed file size on disk to 5 instead of 3 MB.

"Document Ancestors" caused by outside files imported into an image can increase the file size tremendously.

[Abambo]

John-DDB  wrote

Shows the files are exactly the same when fully uncompressed so nothing is changing.

That's what is to be expected by "lossless" compression. It's the same with Photoshop psd format or Tiff with ZIP or LZW compression. And there are other formats also allowing for nondestructive compression (even with gif, the compression is nondestructive).

Non-destructive compression does not work well with natural scene images, like a picture of a tree. Those are typical candidates for JPEG compression where the compression effectiveness is directly related to the picture quality.

With PNG the difference between large, small, smallest is the effort Photoshop put's into compression. But in all situations, the compression is lossless, meaning that the original and the uncompressed picture will have no difference at all. And a tree picture would show very little compression success with PNG, regardless of the compression.

Compared to JPEG you will have a different picture each time you save.

Each time Photoshop reads a picture, it gets decompressed. If you save, it gets re-compressed, even if there were no modifications.

[gener7]

Any file opened in Photoshop is uncompressed. You know this when you look at Image > Image Size dialog.

So when you save using the Large option, it will be compressed for disk storage. Open it again in Photoshop and Image Size will give you the uncompressed size to work on. Save it without modifications using png Large and the size on disk will be about the same as before.

When CS6 saved pngs the only options were None and Compressed. Large in CC applies a faster compression as opposed to none.

Now I let Photoshop do png compression on the fly. It's more efficient at it than using a third party compression utility

[mike224871152qi1]

Seems to be a bug..  i have to go to my old computer and us cs6 to get the png file to save smaller...  

The place i need to get the png file uploaded to has a 3 meg limit but at all compressions i get a 7meg file

i got to cs6 and save as.. and the file format goes down to 2.5 megs... there is not much to it .. move of it is transparent.

BUG

[mike224871152qi1]

Tried another PNG file... ;

Photoshop 23.1,0 on a new macbook max

file size is 7megs.. .large, med and small

then i got to my older make and use Photoshop CS6.. open the same png file and resave it.. goes down to 594kbs... WOW!!!

BUG BUG.. how do we report this.

[D Fosse]

Is this a Save, as opposed to Export or Save For Web?

In that case it's possible the file contains a lot of  "DocumentAncestors" metadata. This is a complete history of paste and place operations, and it can sometimes accumulate to astonishing sizes - e.g. if the file has been used as a template, or is copied from a file used as template.

Export will strip it out, and Save For Web with metadata set to None or Copyright only.