From: Alan Friedman <alan@greatarrow.com>

Date: January 9, 2008 7:55:38 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] tips for alignment of RGB channels

Hi Antonio,

I prepare the RGB image in Photoshop - here is the process I use:

1. Process the R, G and B images as separate files in Astro IIDC then open them in Photoshop (perform any final adjustments in PS)

2. I start with the red document, duplicate the background layer and name this new layer as "red" and the background layer as "RGB". (Be sure that this document is set up as an RGB document and not grayscale!)

3. Copy the green image and paste as a new layer above the "red" layer, rename as "green". Repeat this step with the blue image.

4. Carefully align the green and blue layers to match the red layer. Increase the image size if necessary for finer nudge movements. (I do this by changing the PPI value from 72 to 144). 

5. Create a new layer between each of the color layers. In these new layers, >select all< and then fill the empty layer with a background color (usually black). Then merge the color layer above down to the new background layer. This removes any transparency areas from the previous cut and paste operations giving each color layer an identical background. You might need to rename the layers at this point with their color name.

6. The RGB image is created by copying each color layer and pasting it into the correct channel in the "Channels" palette. Care must be taken to make sure that you have the proper layer visible and selected when you do this. Go to the top layer (Blue), being sure that it is visible and selected. >Select All, and copy. Now select the bottom layer (named RGB) and make invisible each of the color layers on top of it. Go to the Channels palette and click in the blue channel to select it (the other color channels should be deselected, ie not highlighted). Paste. This will place the aligned blue image in the blue channel for the RGB layer. Repeat this process with the second layer (green), being sure that this layer is the only one highlighted and visible. Copy, then select the bottom layer (RGB), making the other layers invisible. Go to channels and select the green channel and paste. Repeat with the red image. Once this is completed and you select the RGB channel (all channels are then active) and go back to layers, the bottom image named RGB will have become your color composite.

7. Be sure to save the document at this point before experimenting with any color adjustments.

8. I retain this document as my working file, keeping the original RGB images invisible but retaining these layers as a reference. If needed, a luminance layer can be created and placed above the RGB layer. I find this helpful on Saturn and Jupiter - for mars, I think the RGB document is generally the most accurate representation.

hope this is helpful.

best,

Alan

On Jan 9, 2008, at 4:04 AM, aa27100 wrote:

Hello,
I am new to this group and to planetary imaging as well, so please don't bother if I ask some
basic questions. I am trying to practice with Astro IIDC and a DMK camera, but would like to
know which tool/tips you suggest for aligning RGB images acquired separately through a
filter wheel. Indeed, it does not seem that Astro IIDC can do that easily, is that right?
I suppose that resampling each channel and layering with Photoshop may be one way to do
that manually. What do you suggest, anyway?
Thanks a lot!

Antonio

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