Image-Processing with IRIS

9. Aligning and Stacking the RGB Channels

Each channel must be aligned and processed independently. Register the R sequence, stack, and then save it. This step is repeated for the green and blue channels.

To align the red channel, load the first image by running the command load r1, then register the sequence by defining the selection area using the mouse, and then running the command pregister r r_pregistered 256 1160. This command aligns all the images with the generic name r and then create and save a new set with the generic name r_pregistered (you may use different name). The 256 pertains to the size of the alignment area. The 1160 pertains to the total number of images. It may take a while to register all the 1160 r images.


To stack the red channel, run the command add_norm r_pregistered 1160. This command adds and normalizes (adjust to an appropriate level) the images with generic name r_pregistered1 up to i_pregistered1160, stacking a total of 1160 images.

As soon as you hit enter, the screen will display images being stacked one after another. The screen is expected to show white, as a result of stacking a thousand image. Use the THRESHOLD sliders to display the image properly. The stacked image should look clearer with less noise.

You may save this file into the Working Folder by clicking FILE > SAVE and then saving it as red.fit. Later on we will load this image into a toolbar together with the stacked green and blue channels.

To align and stack the green channel, run the following commands: type load g1 to display the first image in the g sequence, then use the mouse to drag a rectangle and select the planet. Align the image sequence by typing pregister g g_pregistered 256 1160, then register by typing add_norm g_pregistered 1160. Save this file into the Working Folder by clicking FILE > SAVE and then saving it as green.fit.

To align and stack the blue channel, run the following commands: type load b1 to display the first image in the b sequence, then use the mouse to drag a rectangle and select the planet. Align the image sequence by typing pregister b b_pregistered 256 1160, then register by typing add_norm b_pregistered 1160. Save this file into the Working Folder by clicking FILE > SAVE and then saving it as blue.fit.

Here’s how the command toolbar looks like. Take note of the repeating pattern in the command’s syntax, because each channel has to be processed separately.

At this point, you should have three separate files, one for each channel: red.fit, green.fit, and blue.fit. We can now combine them to form a color image.

Night Sky in Focus | Astronomy and Amateur Radio
© Anthony Urbano | Manila, Philippines

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Eteny

du1au@nightskyinfocus.com

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