Photoshop edits

[mbalensiefer]

Hi.
 When I make corrections to images in Photoshop and leave said edited file "open", and then correct again (and again) using layers and various other PS utilities, is the original file destructively edited each time I effect a change, or is the file effectively edited only "ONCE"; which would be when I tell PS to "save/save as"?

[Jeremy Roussak]

Hi.
 When I make corrections to images in Photoshop and leave said edited file "open", and then correct again (and again) using layers and various other PS utilities, is the original file destructively edited each time I effect a change, or is the file effectively edited only "ONCE"; which would be when I tell PS to "save/save as"?
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You are editinga copy of the original file, in memory or cached on disk depending on various factors. The original file remains untouched until you save your changes. In that respect, PS is like any other document-based application: Word, for example.

Jeremy

[dalethorn]

......The original file remains untouched until you save your changes. In that respect, PS is like any other document-based application: Word, for example.
Jeremy
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This is a good answer as far as the disk file goes, but there's also a question about how much destruction or loss takes place with each successive edit before the final save to disk.  In this case, I would advise the user to experiment (or read some tech papers) to find the best way of sequencing those edits, so the least destructive actions are performed the earliest, etc.

[digitaldog]

With adjustment layers, the damage is done when you flatten or print the doc. Until that time, they are floating above the unmodified data. Eventually you have to pay the piper.

[Eric Myrvaagnes]

If you have sufficient hard disk space available, you might want to do a "save as" early on, with a slightly different name from the original file. Then you can later save or flatten or print knowing that you can go back and start over if you don't like the results.

I save all of my originals completely unaltered, and as I have learned more about PhotoShop, I have often revisited earlier images, doing a much better job the second time around.

[mbalensiefer]

OK--many of these posts confirmed my thoughts.
 The saving grace here, I am thinking, is that WHILE images are still in the editing process (whether merged or unmerged), all edits are done in the .psd domain (instead of .jpg)...only transforming into .jpg when I choose the final "save/save as"...

[dalethorn]

In my 15 years of photo editing, I've found that once an image has been stored as a JPEG, there is virtually no further loss of info from reloading and resaving the image, even 100 times.  The greatest losses that occur are the initial conversion to JPEG, resizing, cropping, rotating, color changes, etc.  Most of these lossy edits point to why people shoot RAW and edit accordingly.

[Dale_Cotton]

Another essential concept here is 16-bit vs. 8-bit. Ultimately, whether an image file is output to screen or to printer or to JPEG, it is telling the device to put a dot of RGB( 143, 18, 220 ) here and a dot of RGB( 140, 23, 187 ) there. An 8-bit file contains RGB values just like that, but a 16-bit file contains values that we could think of as being more like RGB( 143.233, 18.749, 220.007 ).

When you apply a curve to an 8-bit number like 143 it has nowhere to go but to another whole number. It could stay 143 or mutate to 142, for example, but if all it really needs to do in order to respond to the curve is to go from 143.233 to 142.458, then Photoshop has no choice in 8-bit land but to make it 142.0. Then if you tweak the saturation, Photoshop starts with 142.0 and maybe now it becomes 144.371, but again the decimal has to be discarded so we get 144.0 instead. By using layers and masks/selections we can defer all the calculations, so 143 stays 143 until the end and at that time all the various curves, hue changes, etc. can be mathematically squashed together and applied as one tweak to 143. So if the curve wants to add -0.542 and the saturation wants to add +2.371, then Photoshop can add 1.529 to 143, round that to 145, which may be closer to your intent than if it has to perform the rounding for each calculation, accumulating rounding errors each time.

If you work in 16-bit, however Photoshop can save 142.577 after the curve is applied, then 144.062 after the saturation is applied, etc., achieving much the same preservation of subtlety as layers and masks achieve in 8-bit work.

From what I've read human vision is fairly insensitive to differences in RGB values smaller than whole numbers can accommodate. So 8-bit output is not such a terrible thing. The advantage of 16-bit is that it allows us to output a more nearly optimal 8-bit file with perhaps fewer headaches than when we were forced to work in 8-bits.

[Yes: I know there is now such a thing as 16-bit printing, so working in 16-bit has even greater utility in that context. Yes: I know 16-bit RGB values aren't stored as decimal fractions; I used decimal fractions as an analogy. And yes: layers and masks still have great value in 16-bit land because they allow us to revisit each decision. ]

[mbalensiefer]

Thanks, Dale!

Michael