On Wednesday 24 August 2005 14:54, Rikard Johnels wrote:

Hi all!
I have a "problem".
I have two images taken with a few seconds difference, and i want to subtract the differences between them from one of them. Its a crowded square, with people walking around, And i want to "keep" all the stationary object, as benches etc, and remove the things that have moved. Its a experiment to "enhance" pictures taken for a panorama of populated areas.

Any pointers on where to look for a solution?

Well...for strcit "subtraction of an image" - the GIMP provides layer modes taht do that.

Just open both your images as different layers on teh same gimp image, and change the one on the layer above to "subtract" or "difference" - that will do a subtraction on the RGB pixel value of each pixel.

That is not your intended final result. But from the "difference" layer mode you should get everything that is fixed in place (ground + benchs + billboards) in black or near black (with outlines since it is little likely that the images will match exactly at pixel level), with negative or otherwise color distorted sillouetes of the moving objects (e.g. persons + dogs + vehicles) . You can then copy this "silloueted" view with "copy visible" and paste it as another layer. Then yoiu can try different ways of getting this "sillouete layer" to the layer mask of the top image, to trying to let only the parts where people appear transparent. You will need to work a lot to find good combinations of operations to do on the layer masks (you will have to blur + play with curves or levels on them)

I think what you desire would be easier with three instead of two photos from the same place - or your sillouete layer will contain data of people on both photos. With three photos you have to further generate a second sillouete layer, and then combine both sillouetes to generate a suitable mask for one of your layers.

It will requiere quite some experimenting - and I know this I am writing must be sounding confuse. If you have three photos of the same place, mail me (it can be reduced resolution version) of then, and I might try to document all the steps in detail.

If you just have two images, send then anyway ... but it may be harder.

Regards,

JS
->

/Rikard

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Am 24.08.2005 um 21:12 schrieb Joao S. O. Bueno Calligaris:

It will requiere quite some experimenting - and I know this I am writing must be sounding confuse. If you have three photos of the same place, mail me (it can be reduced resolution version) of then, and I might try to document all the steps in detail.

If you just have two images, send then anyway ... but it may be harder.

Yeees, and if it works, Joao makes short tutorial and puts it online - - please. That is exactly the kind of stuff people need to get done with that tons of digital pictures we all take today :)

Seriously, I think after we got an almost complete GIMP reference manual by now, we need to focus more and more to use cases like the one from Rikard.

Regards,

JS
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just my 2c Axel!

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Live is like a chocolate box, you never know what you wanna get... GPG Signatur auf http://wernicke-online.net/Impressum/ prüfen

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Rikard Johnels wrote:

I have two images taken with a few seconds difference, and i want to subtract the differences between them from one of them. Its a crowded square, with people walking around, And i want to "keep" all the stationary object, as benches etc, and remove the things that have moved.

Try this:

Make the two exposures into two layers in a single image. (Align them if necessary.)
Create an opaque layer mask on the top layer.

Now, painting on the mask should reveal the bottom layer. Just paint over any moving objects on the top layer, to reveal the fixed background on the bottom layer. (Making the top layer slightly transparent will help you to predict what will be exposed.)

When done, apply the layer mask to the top layer, and flatten the result.

Does that do what you need?