CS3 Image Stacking feature...

[hozepipe]

Hi

I don't yet do astro photography but I am an experianced Photoshop user (10+ years professionally) and I noticed that in the CS3 beta there's a new feature that allows you to import a movie as a stack of layers directly. I just tried it and it works great. You can even set the range of frames to import before hand.

Anyway that's all well and good, but you need a way to manipulate all those frames. You can't shift-select layers and chnage their blending mode (eg to Screen or Linear Dodge to build up the brightness) en masse. But you can easily create an Action to speed this up:

Select the topmost layer in the stack, change its mode to Screen

Open the Actions palette, create a new Action name it Screen Below or something, hit Record

Press 'Alt-[' ('Option-[' on an older Mac keyboard) to select the next layer below

Change the blending mode to Screen

Press Stop

If you switch the Actions palette to Button mode you can just keep pressing the 'Screen Below' button to brighten the images by blending as many frames as you like.

Create other Actions for other processing techniques (such as returning the mode to Normal, reducing layer opacity etc) and you're laughing. Build a kit of Astro-realted actions.

I'm assuming that this is what image stacking is all about (ie you stack multiple frames from a movie so that noise, which is random in the frame, is suppressed) - I may have not understood the stacking concept but the basic technique is applicable to all kinds of processing work I think. Of course you can still do this in CS2 though I think you'd need to use something like Photo Montage feature and have previously exported the animation into a series of stills before importing into PS.

Hope this helps.

[MartinB]

You are right hozepipe that stacking has the effect of reducing noise. However the stacking process doesn't normally increase the brightness levels of individual pixels. In a typical "average" combine all the values of a given pixel in an image are put together and that pixel is then assigned the average value. This then gives you a much more reliable value for that pixel which greatly reduces the effect of random errors or noise. The image is then "brightened" by stretching the histogram.

[hozepipe]

Ah right - I don't think Photoshop accepts maths in its numeric fields otherwise I you create an Action that set the right opacity for averaging layers.

[Caz]

Hi Hozepipe,

At the moment I'm trying to learn more indepth stuff about CS2, its a fantastic piece of software! So I hope your prepared to have your brains picked once or twice.

10 years eh, thats a whole lotta photoshop knowledge... 8)

Caz

[hozepipe]

Yes, I'm happy to help with any PS questions - I need plenty of help with astro stuff!