File Sizes

RA
Posted By
Richard_Archer-Jones
Jun 22, 2004
Views
555
Replies
24
Status
Closed
I’ve always been confused by file sizes, how they don’t seem to be consistent. Two questions:-

1. Why is it that when I change a 72 pixels/inch psd file to 300 pixels/inch with no resampling or constraining of proportions that it can change from 697KB to 158KB?

2. Why is the file size stated in the Open window so different to the Status Bar size? There are two figures in the Status Bar and I thought the first figure was the file size when flattened and the second figure was the true size (near enough) with layers etc.. I have a file that has no layers or paths and shows as 158K in the Open window but yet the two figures in the Status Bar are different and niether of them is anywhere near the Open window figure (299K/387K).

I don’t expect the figures in the Open window and the Status Bar to be exactly the same but there is quite a big difference sometimes. Of course, a difference of 150KB wouldn’t be so great if the file was bigger but I’ve found another file, a tiff file, that’s 2.32MB/1.82MB with no layers or paths. The Open window agrees with the first figure on that one. What’s happening here?
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CW
Colin_Walls
Jun 22, 2004
Why is it that when I change a 72 pixels/inch psd file to 300 pixels/inch with no resampling or constraining of proportions that it can change from 697KB to 158KB

So are you saying that you open a 697Kb PSD file, change the resolution to 72ppi [no resample] and save the file again; then it is 158Kb?

The pixel size was unchanged?
MM
Mac_McDougald
Jun 22, 2004
…with no resampling or constraining of proportions that it can change from 697KB to 158KB?

Because you started with TIFF and saved as JPEG?
Or saved as TIFF with LZW?
To echo Colin, double check your settings: how many pixels did you start with and how many did you wind up with?

M
RA
Richard_Archer-Jones
Jun 22, 2004
I’ve tried it again and the same thing has happened. Colin, other way around, changed from 72 to 300p/i and then save file. The pixel dimensions, width, and height remain the same and I’m starting with a psd file and ending with a psd file.

It might just be this one file because I can’t repeat this with other psd files, although I did change a tiff file from 100p/i to 300p/i (no resampling etc.) and it changed file size from 235 – 599KB.
MM
Mac_McDougald
Jun 22, 2004
The pixel dimensions, width, and height remain the same

If you have changed ppi, the width and height in inches/cm can not be the same as the original if the pixel dimensions are the same as original.

M
CW
Colin_Walls
Jun 22, 2004
Subject to your reply to Mac’s comment, I’d be interested to see the file and see if I get a similar size change. If you want, please email to colin_walls AT yahoo DOT com
MM
Mac_McDougald
Jun 22, 2004
The only ways I can think of that a psd file could get larger re-saved at the same pixel dimensions:

– adding layers, channels, whatever, before saving
– going from 8 to 16 bit (but this should be very close to exactly twice the size)
– starting with grayscale or bitmap, changing to RGB. Grayscale is 1/3rd RGB size, at least in TIFF format.

M
RA
Richard_Archer-Jones
Jun 23, 2004
Mac, yes, the dimensions in inches change (should have mentioned that). I didn’t change any of the items you mention, but remember, this file is getting smaller. I remember now that this was a file that someone else did and I put on my PC via a floppy disc and I’ve discovered something strange. All I have to do is save this file under another name, without altering it in anyway, and it changes file size from 697 to 158KB. If it’s to do with file compression when saving it onto the floppy wouldn’t it get bigger on my PC? The same with that tiff file I mentioned, all I have to do is save it as another name and its file size changes, but this time it gets bigger and that file I created on my PC …. strange isn’t it?

Thanks Colin for the offer, if you want I can still send it you.
CW
Colin_Walls
Jun 23, 2004
This really sounds like it’s a TIFF with LZW.
MM
Mac_McDougald
Jun 23, 2004
This saga has gone all over the place.
Supposedly a psd to psd file?
Maybe.

Whatever.

Email it to me if you like, I’ll be happy to see what’s up with it.

doogle AT doogle DOT com

M
L
LenHewitt
Jun 23, 2004
Richard,

Sounds like you are not embedding an ICC profile whereas previously the file had an embedded ICC profile.
RW
Rene_Walling
Jun 23, 2004

1. Why is it that when I change a 72 pixels/inch psd file to 300 pixels/inch
with no resampling or constraining of proportions that it can change from 697KB to 158KB?

Where exactly do you find these numbers (697Kb and 158Kb)? In the explorer window? In the PS image size dialog box?

Are you resaving on the file on the same disk?
MM
Mac_McDougald
Jun 23, 2004
400+KB diff?
I doan theek so…

M
RA
Richard_Archer-Jones
Jun 24, 2004
Mac, there’s nothing supposedly about it, it most definitely is a psd to psd file. There’s definitely something wrong with it, when I attach it to an e-mail (to send to you) it can’t be viewed, launched, or detached. The message comes up "Note item not found". I’m off now, have another go next week perhaps.

Len, I don’t know what ICC files are. Remember it gets smaller.

Rene, I find those numbers in the Photoshop Open window, and I’m saving on the same disk, my hard drive.

There’s still the inconsistency in the Status Bar and Open window figures to try and understand aswell (see my first post).
MM
Mac_McDougald
Jun 24, 2004
when I attach it to an e-mail (to send to you) it can’t be viewed, launched, or detached.

??
Just attach it and send…you don’t need to "view" or "launch" it.

You can also upload it my FTP site if you like.
Use upload link on homepage at doogle DOT com

M
L
LenHewitt
Jun 24, 2004
Richard,

The message comes up "Note item not found<<

Aha! That sounds like there was a Note attached to the original which has been discarded when you re-saved. This will happen if the Annotations check-box was not checked when you saved the file
MM
Mac_McDougald
Jun 24, 2004
Good catch, Len…
It didn’t ring a bell for me, but it should have.

M
MM
Mac_McDougald
Jun 30, 2004
And it remains a mystery.

This file is 301 x 339 pixels.
It is a single layer file (no background layer) with a logo type image knocked out with transparency around it.
8bit RGB.

The mystery is: the .psd is 698k

Can resave exactly the same as .psd (still single layer with transparency): 165k which is about normal.

The original file has no audio or text annotations, has no embedded color profile, no ITPC or EXIF information.
No additional channels beyond the RGB.
No layer effects, no paths, nada.

Only thing never mentioned in this thread is WHERE the .psd came from? I guessing that it was made in some app other than PhotoShop, where the ..psd writing is somehow just "sloppy".

I must admit, I’m intrigued. Did a couple of experiments: a similar image saved as .psd from PaintShopPro 7 and resaved in Photoshop were similar in file size. IrfanView won’t write .psd. Tried Corel PhotoPaint 9: interesting here.
Saved a TIFF image as .psd from that: 300k. Resaved same image as .psd in Photoshop: 74k ! This did not have transparancy as don’t know how to do that in Corel, and didn’t take the time to learn.

So, based on that last little experiment, which shows about the same disproportinate difference, I’m guessing that the larger .psd was indeed created by some other app than Photoshop and it just sloppily "pads" the file.

The only other thing I can think of: I’m still using Photoshop 7. Perhaps PS CS can embed some sort of information in the file that I’m simply not seeing in 7 and the file was saved in CS with whatever info this might be?

Mac
RA
Richard_Archer-Jones
Jun 30, 2004
Gosh, you’ve put a lot of effort in there, Mac. Well done that man.

As to the origins of this file, I can’t help much there as it’s quite some years since I aquired it. Something I do remember that might be significant is that it has got a Mac connection. I don’t think it was produced on a Mac but it had been ‘interfered with’ by a Mac. It was something that was left over after I had been trying to get a Windows document printed by a firm that only had Macs.

I’ve got Corel PhotoPaint 10 and tried what you did and got the same result.

I still don’t understand why neither of the figures in the status bar agree with the Open window’s figure. Shouldn’t one be near enough the same? That anomaly happens on many files.
MM
Mac_McDougald
Jun 30, 2004
I still don’t understand why neither of the figures in the status bar agree with the Open window’s figure. Shouldn’t one be near enough the same? That anomaly happens on many files.

The first figure there is always simply based on pixel count file size, as in flattened TIFF.

Same as looking with Image/Image Size…
In other words, without layers or other additions to file, your original problem image would be 299k saved as standard no layer RGB 8 bit TIFF. Indeed, that is what PS reports in that first figure, and with Image/Image Size/Pixel Size. That’s a pretty straightforward mathematical calculation based on non-compressed TIFF standard. Although Manual says is based on "flattened file in Adobe Photoshop format" (doesn’t seem correct to me, is always closer to TIFF).

The second figure is (as I understand it) estimate of file size with any additonal file info for that size pixel size
(layers/channels/paths/whatever).

The first figure is pretty close to saved file size on disk for flattened TIFF. The second less precise, I’ve found, more of an "estimate".

Saving in PSD or especially JPEG will yield significantly different actual file sizes on disk than TIFF. PSD is proprietary, has some degree of built-in non-lossy compression (or maybe better called efficiency). And of course JPEG will always be smaller file on disk due to lossy compression, and will vary wildly depending on amount of compression (quality setting). Using Save For Web will give a decent estimation of final file on disk size for JPEG at a chosen quality setting. But note that when you open the JPEG back in PS, it will again report size as the uncompressed pixel size in these dialogs, NOT the size of the file on disk. So you can also consider this figure to be pretty much the size in memory needed to open the image also.

The only big mystery on your file was the initial large file size for the pixel dimensions, much larger than PS reports in either of these dialogs. Which brings me back to same conclusion, that the .psd file was created in some application that, while it is a valid psd, is really padded with extra "null" information of some sort, due to non standard algorithm the program used to make the PSD in the first place.

Maybe someone else will chime in and explain better than I can…

M
RA
Richard_Archer-Jones
Jul 1, 2004
Wow, thank you Mac. Loads of information there. I’ve studied it, but I need more time to study it properly.

Sorry to find fault with such a comprehensive reply but have you forgotten something? Is there any mention there as to the figure displayed in the Open window? I couldn’t find it. I mean when you click File / Open and hover or click on a file, the sizes given there quite often are nowhere near any of the figures in the Status Bar (Image / Image Size).

Many of my files show this discrepancy, some are only a few KBs out, I’m not on about those, it’s the ones that are way out. For instance, one psd file shows as 205KB in the Open window but the Status Bar states 2.38M/3.84M; it has 3 extra layers but I would have expected the first figure (2.83M) to be the figure displayed in the Open window. Some files Open window figure don’t match the Status Bar figure even when they have no layers etc.. What are the Open window figures? Those are the figures I usually judge by.
CW
Colin_Walls
Jul 1, 2004
one psd file shows as 205KB in the Open window but the Status Bar states
2.38M/3.84M

Surely anything else would be more surprising?

A PSD file is compressed [non-lossy, of course]. The memory image isn’t.
RA
Richard_Archer-Jones
Jul 1, 2004
Colin, I think you’re asuming I know more than I do. What’s this about memory image?
CW
Colin_Walls
Jul 1, 2004
What’s this about memory image?

The image data is a certain number of bytes. When loaded into PS [into memory] that is the space it occupies. It’s size is a function of the pixel size of the image, the number of layers and other data that may be attached. When the data is written out, the format of the file bears very little similarity to the data that was in memory. It is likely to be compressed in some way. How much and how it’s done will depend on the file format.

So expecting PS’s idea of an image size [per the status line] to resemble the file size in any specific format is not reasonable.

Have I elucidated the matter or confused you further?
MM
Mac_McDougald
Jul 2, 2004
The basis of what Colin is saying is that an image of x by x pixel dimensions will have a basic size in memory, and this is constant. Doesn’t matter what the image consists of.
An 800×600 pixel 8 bit RGB image will have the same size in memory regardless of what the image consists of, all black, all white, all red, or thousands of different colors.

It just so happens that this also coincides quite closely to the actual size on disk if saved to TIFF flattened format.

Other formats, most particularly JPEG will be MUCH different byte size on disk, as it uses lossy compression schemes. The actual byte size depends on what quality settings are chosen (degree of compression) and makeup of the original image (images with expanses of same/similar color will compress more, etc).

So you make a new file, 800×600: PS reports that it will be apprx.
1.37MB. Save it as TIFF, and you’ll get pretty close to that size on
disk.
Save as JPEG and you might get down as low as 10KB!
But open the 10KB JPEG back in PS, it will report 1.37MB pixel size once again.

M

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