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Brian Ellis
29-Jun-2006, 08:50
One reason for using layers is to allow you to make various changes to the image and then if you don't like them you can easily revert to the original by getting rid of the layer. Among other benefits, this is said to prevent pixels in the original image from being destroyed by the changes as presumably would be the case if layers weren't used and instead the changes were reversed manually. However, it's also possible to reverse changes in other ways, e.g. by use of the history feature or by an "edit - undo" command. My question is whether either of these two methods destroys pixels? For example, using the dodge tool to lighten an area destroys pixels (at least I think it does, which is why I seldom actually use it). If I then decide not to keep the dodge and so get rid of that step either through the history feature or by an "edit-undo dodge" command (as opposed to doing the dodge on a duplicate layer) are the pixels destroyed by the dodge restored just as they would be if they had been made on a duplicate layer?

Guy Tal
29-Jun-2006, 09:36
These changes don't necessarily destroy pixels. They just change their characteristics. Sometimes information (as in differentiation between adjacent pixels) is lost but not always.
The history/undo is useful but very limiting - you have to work sequentially. What if you want to undo one change but retain other changes performed afterwards, or if you want to undo a change days/weeks/months after the initial processing?
Either way - an "undo" simply reverts to the previosu state (as opposed to applying a mitigating action) so any information lost will be regained.

Guy

David Luttmann
29-Jun-2006, 09:37
Brian,

Undo reverts back to the previous history state, and as such, there is no damaging effect to the pixels. Working with a 16 bit file allows for a fairly large margin of error in terms of correcting mistakes. As long as you are working within the tonality range of the 16bit file, you can freely use the burn & dodge tools.....keeping in mind that you can only go so far depending on the quality of your scan.

Regards,

Gordon Moat
29-Jun-2006, 10:21
The best method is to work on a copy of the original scan, and not on the original. While this can mean more storage requirements, it makes it very easy to go back and work on it again. One aspect of layers is they can be copied from one document to another easily; if you find something you want to repeat over different images, or another copy of the same image, they are easy to transport.

It is correct that PhotoShop performs destructive editing. However, you seem to be implying that destroy means removes; short of using the eraser tool, it is not often you would be removing pixels. Rather, the original pixels are altered in some manner. Nearly all operations in PhotoShop can cause an alteration of pixels, which is why many call it a destructive application.

A good working practice is to get as good a scan as possible, then only alter the image enough to match your chosen method of printed output. Unfortunately, sometimes scans are not optimal, or the scanner is not as good as one would hope, or the scanner operator did not quite get it the way you wanted. In such situations, or when doing composite images, or when altering the tonal relationship of various hues, then manipulating the image might be your best choice. When you are learning, or not sure of various results from some actions, work on a copy of the original, and keep alterations as minimal as possible to get to the results you want.

Ideally, you are trying to match the printed output to the original scene, or your concept of the original scene. Simply matching the printed output to the monitor can miss some aspects of the original scene. If you are working from chromes, then you can compare the printed output to the original film. Other than those aspects, keep practicing and PhotoShop will become easier to work the way you want it to.

Ciao!

Gordon Moat

Greg Miller
29-Jun-2006, 11:10
History Brush and Undo only survive as long as the file is open. If you close the file and open it later (next day, next year,...) those states are gone. Applying a level or curve to the background layer (or a copy) does change pixels. So, for example, if you apply a level to the background layer and move the balc point to the right, you cannot reverse that later after you close the file.

I lile to work in multiple sessions. I'll do some editting and then take a break. usually when I come back with fresh eyes I see changes I made that I do not like. Sometimes this happens week or months later.

Kirk Gittings
29-Jun-2006, 12:33
What Greg said.....Why I try to use adjustment layers as much as possible. It is important even to let your test prints dry over night when you are getting close to a final print as there is some dry down. Also my tastes change over time and adjustment layers allow me to tweak tones to suite my current mood.

Brian Ellis
29-Jun-2006, 16:29
Thanks for the responses.

Greg Miller
3-Jul-2006, 13:05
An additional thought. Layers provide the added ability to set blending modes. Blending modes are very powerful in their ability to produce effects very similar to dodging and burning.

Frank Petronio
3-Jul-2006, 22:04
All this is fine until you try to work with a huge file on an underpowered and low memory PC. In 1995, a 20mb file was "huge". Now 500mb files are only "large." It's human nature to keep pushing to the limits of your gear, and people always seem to go larger than their machines are opitimized for.

So you might consider working "old school" and saving numbered versions as you go along making hard edits to a single layer file -- when you have to work on large stuff. Try it both ways and see which is faster for your range of files. I still do a lot of old school single step work when I know I have a safe earlier version already saved. It can be a lot faster.

The other thing to do is to make as few destructive moves as possible. It is better to do everything you can in one step using Curves, than to bounce back and forth between Levels, Hue and Saturation, back to Levels, etc. to get to the same place. Incremental steps are what are destructive to those poor pixels.

Jack Flesher
4-Jul-2006, 08:16
An additional thought. Layers provide the added ability to set blending modes. Blending modes are very powerful in their ability to produce effects very similar to dodging and burning.

I agree with working in layers and do so myself, but I want to clarify a fact for this post: You can also set a blend mode if you add an adjustment directly to a file.

Immediately after you apply say a curves or any other image adjustment, you go to Edit>Fade Curves (or whatever adjustment you just did). In the dialog box that pops up, you can set opacity and blend mode just as though the adjustment had been done on its own adjustment layer. However, it is only available immediately after applying the adjustment and is gone forever if you do anything else. It is also not editable after it has been applied. Obviously I am not endorsing this as a workflow methodology, but wanted to clarify it is possible to do in a non-layered workflow.

Dominique Labrosse
4-Jul-2006, 21:15
Another way of making "destrucive" changes safely is by copying the original image (often on a layer named "background") and pasting it onto another layer (underneath your adjustment layers) then making your dodge/burn adjustments. If you go too far or somehow wreck your image, you can simply make another copy and try again. However, Frank's advice hold true. This is an easy way to make very large files.

Greg Miller
14-Jul-2006, 11:52
I just saw this dialogue involving Photoshop guru Tim Grey:

On Monday, 10 July you responded to the question:

I would like to apply a blur effect to a single image (a portrait) as though I had done two exposures on film with one in focus and one out of focus. But I want to be able to keep the eyes sharp without the halo effect of the blur. Is that possible?

I notice there was no mention of using the History Brush tool to reduce and/or eliminate the blur previously applied. Is there any disadvantage to using the history brush tool?

==========

My problem with the History Brush tool is that it requires you to directly alter pixels in the image. I would very much rather mask away the blurred areas that you want to appear sharp in the image. The net effect is exactly the same as you would achieve using the History Brush, but the difference is in flexibility. If you decide later that you've hidden too much of the blurred area and want to bring it back, you don't have too many options when the History Brush was employed, unless you've been careful about taking snapshots or you have caught the error before getting too far into your work. With a layer mask, on the other hand, you can simply modify the mask (paint with white to reveal) to bring back the blurred areas. As far as I'm concerned, this approach is much better than the use of the History Brush tool, so I never use the History Brush. Ever. I always employ a layer mask in situations where I might otherwise use the History Brush.