Participant

Question

Saving png files in Photoshop

Forum|Forum|6 years ago
July 13, 2019
3 replies
11901 views

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!

This topic has been closed for replies.

M

mike224871152qi1

Participant

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

M

mike224871152qi1

Participant

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

Community Expert

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.

J

johng9625402

Participant

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

Community Expert

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.

ABAMBO | Hard- and Software Engineer | Photographer

J

johng9625402

Participant

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

Community Expert

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.

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