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I'm not writing about a tool available only in some unstable development or future release of Gimp , but of feature already available in any recent stable version of gimp ...

But , please don't waste your time to search it in the toolbox or in some menu...you would find nothing alike because is well hidden

We can even state from a very theoretical , almost philosophical point of view that something as a “undo” or “history brush” in gimp doesn't exist or at least don't exist yet..(see NOTE 1)

But will be pointless worry about the theoretical existence of the history brush , since in practice in the real word it it works very well and could be activated with only 2 click even if it has not its own icon

So... what is a "history brush" and why we could need one? what we can do with it?


HISTORY BRUSH

In Gimp a layer could be at same time invisible and active and in this case could happen that some mistake is done and unnoticed till too late

With the “undo” function we can revert the image to any previous state...but in this way we will lose all the work done after that point.

“undo” will revert the whole image...to revert only a selected part or to be more exactly to stroke the “undo” in a customer chosen area we need a different tool: a “undo” or “history” brush

in other words the “undo (or history) brush could “paint” and merge previous version of the image on a user chosen area ...

The only limit of the “Undo” and of the “Undo (or History) Brush is that need a “image history” to use, so they could not work if the image was closed (Till now there is not option to save the history of the image within the image file )

The UNDO ( or HISTORY ) brush work in a similar way to the "Undo". but instead then on the whole image its effect could be applied on chosen area ,with brush strokes

[NOTE] link about "Undo" and "Undo history"
http://docs.gimp.org/en/gimp-concepts-undo.htmlhttp://docs.gimp.org/en/gimp-undo-dialog.html
[url][url]http://docs.gimp.org/en/gimp-edit-undo.html[/url]http://docs.gimp.org/en/gimp-edit-undo-history.html[/NOTE]

CLICK 1: GETTING READY


The basic trick is simple: duplicate the image and work on the duplicate
DON'T close the original...it can be minimized but it must stay open

To make a duplicate we can use “Ctrl+D “shortkey ,or, with the mouse click on : image_menu\image\“duplicate image”



Now to avoid mistakes and misunderstanding we should better rename the original “ORIGINAL_image-source” and the duplicate “ Canvas”

Again DON' T close original ...the duplicate can't duplicate the image "history" but only its present state...if you close the original will be lost the history and with the "history" any chance to use a "history brush"

So now we are ready to use the Gimp History brush at soon we will find its hiding place

CLICK 2 HOW TO LOCATE AND USE THE GIMP HISTORY (UNDO) GIMP BRUSH

The Gimp History Brush is very well hidden in usually overlooked but quite useful setting of the clone tool

So focus on the duplicate (what we called "Canvas") and from and then hit the “C” key (or with the mouse click the clone icon in the toolbox) to open the CLONE Tool setting
. .and then chose those options

.

[NOTE] Please note the setting :

1 SOURCE : Image Source
2 ALLIGNEMENT: Registered [/NOTE]


This setting are the history (undo ) brush
Or, to be correct , with this setting the clone tool could will work exactly as a History brush

to activate you need to hit “okay” and this is the end of “CLICK 2”

CLICK 3: USE THE “HISTORY BRUSH”

Now to chose the right spot as source image go on the original image (the one we called :“Original_image-source”) , and open its "undo history" dialog (as example from "image menu\edit\undo history)



In this way you can chose the best source(s) for the clone tool and use them to retouch the duplicate (the “canvas” image)

You can chose any transparence/opacity setting for the brush and any brush you like

( but something as a round or polygonal brush, resizable on the fly in size, shape and feathering ,is for me the best brush for the task...about use of resizable brush see
http://www.gimptalk.com/forum/topic.php?t=13194&start=1 )

[NOTE]you can even chose a merging mode different then “normal” (as example merging mode as“ligthen only” “darken only” “screen” and “overlay” could be quite useful for retouching...)[/NOTE]

Once done You may import the corrected edited layer(s) back on the original (no need to import all others layers that were not edited) and close the duplicate,
continue to work on the original

and in case of need ,to use again the history brush create a new dup

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NOTE 1

there was a discussion over to implement a proper "history brush http://bugzilla.gnome.org/show_bug.cgi?id=74554 but at the end was planned to add first a even more useful features "edit\fade" that should be available in gimp 2.4 ).

NOTE 2

The same setting of the clone tool could be used to “apply filters or effect with brush_stoke" as explained here
http://www.gimptalk.com/forum/topic/How-To-Stroke-Filters-With-Brushes-14120-1.html

NOTE 3

I was checking the links...
And while i was browsing the very latest Gimp Help .... at the very bottom of the page on the Clone Tool i found a very similar suggestions as you can see here:

http://docs.gimp.org/en/gimp-tool-clone.htm

This is not surprising till the most useful tips ,even about the most hidden and\or overlooked Gimp features could be found on the Gimp Help, that is the best book never written on Gimp and is available even online
(you can also download a PDF version and print it...)
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I didn't noticed that few lines of text went missed so last step was almost uncomprensible. :a:

I edited and i hope that now everything is clear, if not post your question

No any question , comment of remark?
Too simple or too complex or not so interesting ? Or you already know about ?

Hey, this was actually very interesting. I had to read it twice to understand it but it makes sense to me now :h:.

The clone tool in some way incorporate the brush tool...i mean with the clone you can do everything you do with brush ,with any of your brushes...but the clone can do also much that brush tool can't do

Create quickly "history brush"," unsharp mask brush" and "Filter effects brush" is a good example .



any suggestion to make it more intutive in a way it doesn't need to be read twice, is really wellcome :h:
(I allways forget to take screenshoot when i use it...)

You worded it well, it was just hard to understand because it was a bit complicated.

Nice info. Thanks fotocomics :h:

Very interesting, I did not know about this. Nice tutorial man!

Hmmmm... it is not a true history brush, unless I misunderstood.

Because if you keep modifying the 'canvas' image after the 'history tool' has been applied from the 'original' image, the 'original' image's undo history dialog will not be update with the changes made on the 'canvas' image, and therefore subsequently become useless.

Then only workaround (and overkill), is , once finished with the 'historic' changes on the 'canvas' image, copy its contents to the 'original' image, and then, when needed, duplicate the 'original' image, thus creating a new 'canvas' image, using the clone tool ... you get the loop.

Still useful tutorial. And correct me if I am wrong about the procedure.

in theory you are correct

In pratice that do not seem to me too relevant..the original image contain all history till point D (=duplicate imagine )
the duplicate contain the history after, but that is only the history of the correction

You may import the corrected edited layer(s) back on the original (no need to import all others layers that were not edited) and close the duplicate,
continue to work on the original and in case of need create a new dup

Obviously what i described is not a true true history brush but emulate most of its features.

I fear the project for a "true" history brush for gimp was abandoned, as the idea to add to the save dialog a option to save also the imagine history , maybe for its drawbacks (as example much bigger file size , and necessity of create a new type of file that may contain that data, and that will be hard to open with older Gimp version).

Personally i do not find relevant the size problem since HD offers more and more GB , and DVD are quite cheap

It depends, if you use GAP, multiplying the augmented file size for each frame, becomes significant. But an implementation of a history brush would be nice.

Whereas I see the point with wanting to retain the undo history of the original image, in practice I think I would rather keep working on the original and simply extract duplicates at key points of the work process (i.e. just before trying something potentially "dangerous" to the painting). These copies then act as temporary snapshots -- and I can use them as clone sources if I need to selectively revert a change in the original. This method is of course even less of a proper "history" brush, but for me that way of working is a lot more intuitive.

I think in order to make this tutorial a little clearer, you should probably include an screenshot showing the two images next to each other, with the clone source selected in one of them and painting in the other. It's not intuitively obvious (unless you've seen it before) that the clone tool can actually clone also from separate images.

As for saving the Undo history in the xcf, it would be nice if it was turned off by default but optional, so you could include it in the save if you had no concerns about file size or backward compatibility.
.
Griatch

Good point Griatch i will add a couple of screenshoots

.

i fully agree with this.
Maybe soon will be change in gimp xcf (seems needed to save in 16 bit instead then 8, and anyway to handle new Gegl operations) then may be the time to propose/hope for that added option

DAMN!! also here all illustration went lost