Luminous Landscape Forum

Raw & Post Processing, Printing => Adobe Camera Raw Q&A => Topic started by: Chacaboy on August 09, 2018, 05:58:35 pm

Title: File Size
Post by: Chacaboy on August 09, 2018, 05:58:35 pm
A student asked me to explain why the file size of a psd file indexed on the hard drive, the file size in the Image Size dialogue box, and the file size in the Document Size window in the lower left corner of the image frame, are all different. Does someone know, or can you suggest a reference text for this?

many thanks in advance,

Chacaboy
Title: Re: File Size
Post by: digitaldog on August 09, 2018, 06:16:00 pm
There are a number of reasons but one is, size on a drive is calculated differently depending on the size of the drive, Photoshop can't calculate the size very well of layers, which, depending on the amount of transparency vs. actual pixels alters the saved size, it depends on how the file is sized (examine the differing options for file sizing including backward's compatibly, compression etc). Then there's masks, type layers etc
https://creativepro.com/know-your-photoshop-file-sizes/ (https://creativepro.com/know-your-photoshop-file-sizes/)
Title: Re: File Size
Post by: Chacaboy on August 14, 2018, 12:04:53 am
Very helpful Andrew. Thanks so much!
Title: Re: File Size
Post by: Chacaboy on August 14, 2018, 12:42:37 pm
Can you tell me why a file with one layer is so much larger than a flattened file?
Title: Re: File Size
Post by: digitaldog on August 14, 2018, 12:51:03 pm
Can you tell me why a file with one layer is so much larger than a flattened file?
Again, it depends on what's on that layer. One pixel or half the layer of pixels or the entire layer. Pixels of image data take up space. Transparency doesn't.
Title: Re: File Size
Post by: Peano on August 14, 2018, 04:01:21 pm
Pixels of image data take up space. Transparency doesn't.
Transparency does.
Open a jpeg in Photoshop and save it as a PSD file.
Then add a blank (transparent) layer and also save that as two-layer PSD file.
The second file will be larger than the first.
Title: Re: File Size
Post by: Chacaboy on August 14, 2018, 04:06:48 pm
I understand that it depends on what's on the layer. But if you take one image saved flattened, unlock the layer and save it again it is considerably larger than the flattened one, with an identical set of pixels.
Title: Re: File Size
Post by: Peano on August 15, 2018, 10:30:43 am
I understand that it depends on what's on the layer. But if you take one image saved flattened, unlock the layer and save it again it is considerably larger than the flattened one, with an identical set of pixels.
I don't know why that happens, but I can give you another puzzling fact about file sizes: If you want to reduce the size of a multi-layer PSD file, create a blank layer on top of the layer stack and fill it with white. Leave all the other layers intact. This will significantly reduce the file size. Sometimes useful when transferring a file to someone else.
Title: Re: File Size
Post by: jmlphotography on August 19, 2018, 05:51:28 pm
Peano,

I just tried ctrl>shift>n to create blank layer and filled it with white.  File size was unaffected.

What am I missing?
Title: Re: File Size
Post by: Peano on August 19, 2018, 06:56:30 pm
Peano,

I just tried ctrl>shift>n to create blank layer and filled it with white.  File size was unaffected.

What am I missing?
I don't know. Must be something. Works every time for me.

If you're looking at the document sizes at the bottom of the image window, I don't think those will change. Save the PSD file and then check it's size.
Title: Re: File Size
Post by: jmlphotography on August 22, 2018, 07:21:46 pm
Peano,

Just tried it again on a couple of different files and again made no difference.  Not worth pursuing, but I am using CC2018 if that matters.
Title: Re: File Size
Post by: Peano on August 22, 2018, 08:28:20 pm
Peano,

Just tried it again on a couple of different files and again made no difference.

It won't make a difference in the file size shown inside Photoshop. You have to save the file to disk and then check size of the file on disk. Like this:
Title: Re: File Size
Post by: digitaldog on August 22, 2018, 09:34:52 pm
It won't make a difference in the file size shown inside Photoshop. You have to save the file to disk and then check size of the file on disk. Like this:
Indeed, sorry if this wasnít clear. What PS shows isnít that useful and one needs to examine the size reported in the Finder.