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PhotoShop History


The Little Guy

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How does "History" work in photoshop? When you have an image, and you press "Undo" how does it know what to undo? Or redo?

 

The only thing that I can think of, is that photoshop would save a version of the image, every time an edit has been done, so every time the image changes it saves a copy of the previous image.

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How does "History" work in photoshop? When you have an image, and you press "Undo" how does it know what to undo? Or redo?

 

The only thing that I can think of, is that photoshop would save a version of the image, every time an edit has been done, so every time the image changes it saves a copy of the previous image.

 

Or maybe only 'certian elements'.

 

As if you have applied a effect it's hard to get the original with 'de-effecting it' lol

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OK, yeah, but you have your current edit, how does it know what the previous edit looked like when you press undo?

 

Probably by examining the previous action / state and reverting back to it. Every brush stroke, marquee selection, pixel plot, etc.. is stored. The longer you work on something, the larger the file gets. Once in a while, you can use the purge command to alleviate this.

 

I wouldn't bust my head over the extreme technicalities of how it works.. I for one am grateful for Ctrl + Alt + z to continuously undo things, or Ctrl + Shift + z to march through redos (in the event I go back to far). I don't make use of the actual History palette personally.

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It doesn't truly work by reversing the action history alone, simple actions like drawing lines etc do work that way buy more complex actions like rasteration and re-sampling, create a flag in the actions script that as a link to the a re-storable copy, (a backup if you will) the reason for this is simple, if you have a image 1024x768 and resize it down to 1x1 then resize it back to 1024x768.. its not going to look the same!

 

with that in-mind to you could simply create a backup before any action then the undo just restores back :)

to save space use fifo with 20 actions history.

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if you have the original image, and the list of commands run on that image to reach the current image, you can always go back in time by just reverting to the original image and re-applying the actions up to the point where you want to revert to

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Nice idea, rhodesa but your need to store every action from the start which means some heavy actions at the start going make a simple line undo quite long.. in any case theirs lots of pros and cons to each.

 

as for smart objects.. yes very true but i don't think ImageMagick supports them :P

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