Saving in PDF (Photoshop 7.01).

TM
Posted By
Thomas_Madsen
Oct 20, 2003
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802
Replies
5
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Closed
Hello,

There’s something I don’t quite understand about saving images in the Photoshop PDF format. If I have an image with an adjustment layer for instance, and I save that image in PDF with layers and encodes it in JPEG low quality, will I degrade the image every time I overwrite it in PDF and JPEG low quality encoding again? It seems as if the image only degrade the first time I save it in PDF and low quality JPEG, or am I wrong?

If it degrades every time I overwrite it in PDF low JPEG quality, then I wonder why I can’t see a difference even if I’ve overwritten it many times. Am I going blind here, or does Photoshop only compress image data the first time one saves a PDF with JPEG encoding, but not the following times?

(Hope you understand my bad English).


Regards
Madsen.

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DM
Don_McCahill
Oct 20, 2003
I’m not 100% sure where you are coming from, but if you save a file in PSD format, it does not use JPG compression. So there is no loss of quality.

If you mean starting with a JPG file, then saving as PSD, you will keep the same amount of lost information from the original JPG, but it will not increase (as it would if you saved it as a JPG again).
Y
YrbkMgr
Oct 20, 2003
Don,

When you save a file using File|Save As… Photoshop PDF, you have a choice of how to compress it: Zip or JPG encoding; further you can specify the amount of lossy compression to use.

Madsen,

will I degrade the image every time I overwrite it in PDF and JPEG low quality encoding again?

It depends on what, exactly you mean. While an image is open in Photoshop, when you Save As PDF, of course you compress it, assuming JPG encoding in the options.

But, if you make no changes to the image while open in photoshop, and save it again, there will be no incremental quality loss. If you open a PSD or Tiff, that you’ve saved as a "reference" file, and re-save it as a PDF (probably the best way to do it), then it’s a "firt time" compression.

If you open that PDF page in photoshop, and make a global change, you will increment the amount of lossy compression.

Really, the same rules, generally, apply to PDF’s as they do with JPG’s.

Peace,
Tony
L
LenHewitt
Oct 20, 2003
Don,

Thomas is talking about Saving to Photoshop PDF not PSD………

Thomas,

Am I going blind here, <<

Possibly (although I do hope not!). AFAIK there is nothing ‘magical’ about PDF’s. If you open a PDF and edit and then re-save it, the normal JPG rules will apply. Of course, you will only see additional compression effects in areas that you have changed…..

To proove it, Save as PDF, open and apply Hue/Sat over the whole image and then re-save. Do that a few times and you will clearly see the increased JPG artifacts
TM
Thomas_Madsen
Oct 20, 2003
wrote:

It depends on what, exactly you mean. While an image is open in Photoshop, when you Save As PDF, of course you compress it, assuming JPG encoding in the options.

Yes and I can clearly see that the compression is lossy the first time I save it as a PDF with JPEG quality 0. I was wondering why I couldn’t see changes in the image data when I changed something (like a huge hue shift, as Don suggested) in the saved PDF and resaved it as PDF JPEG quality 0 again and again.

Really, the same rules, generally, apply to PDF’s as they do with JPG’s.

Thanks and that was also what I thought before I got confused .:) The thing that confused me was the following sentence from the book ‘Real World Photoshop 7’.

Quote:
| …And, if you use JPEG compression in the PDF, the PDF image | degrades, but the layered data does not. So when you open it in | Photoshop and resave as PDF, you don’t re-compress (and further | degrade) your data. Very spiffy.

I’m not sure if I understand that statement. What do they mean by ‘the layered data does not’? If it means every layer, including the background layer, then saving as PDF with JPEG compression is different than just saving the image as JPEG, because if you save as JPEG, you degrade your data every time you resave as JPEG.


Regards
Madsen.
Y
YrbkMgr
Oct 20, 2003
I’m not sure either Madsen. That’s news to me. But bear in mind that technically, the background is not a layer, so it would be exempt from the statement.

I am interested, however, in any comments from others on the issue.

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