RGB + L and black edges

[mcbbcn]

Hi,

I'm evaluating a trial version of Pixinsight and so far it looks like an awesome package.

I'm trying to combine an RGB image with a Luminance image of M31, but as a result of calibration and registration, my RGB image has a black edge on the right side and the bottom side which throws off my DBE process, so I know that I need to get rid of them with the Dynamic crop tool.  But my Luminance has the black edge on the left and top sides (and it's a different width than the one of the RGB image), so when I remove the black edges for the RGB and then for the Luminance, I can't combine them anymore because it says that the geometry has changed.

I think I need to use this tool called dynamic alignment before I try to combine them, but I was not sure if I'm following the right steps, so if anybody could confirm that this is the most logical thing to do before DBE, I'll happy to go with the next step.

Thanks for your help,

Miguel

[oldwexi]

Hi Miguel!
My personal workflow for this issue is:
* crop RGB
* StarAlignment - use the cropped RGB as reference, working mode Register/Match
   add the L as view in Target images
   this produces an L-image the same size as the RGB and aligned to RGB.

the reference image has always to be the smaller picture, if L is the smaller one
use L as the reference and RGB as target.
This works always but - there are for sure other solutions...

Aloha
Gerald

[Nocturnal]

Hi,

I recommend this sequence:

- register your images
- combine them
- crop
- DBE

Let us know how that works for you.

[zvrastil]

Hi Miguel,

most straightforward solution in your particular case would be to clip both images by 1 pixel at each side. As there's no intersection in border pixels between two images, you'll probably throw them away in the end anyway. Then, re-aligning images won't be necessary.
In general, for aligning star images use StarAlignment instead of DynamicAlignment. It is fully automatic and it is not prone to human errors. It should work in all cases except difficult ones with heavy field distortion (like when using short lenses).

regards, Zbynek

[mcbbcn]

Thank you all!  What a great forum!!!

[sleshin]

Miguel,

Here's another solution. Set the crop on say the RGB image so that it's dimensions will also crop the undesired portions of the Lum image. Then before you execute the crop on the RGB image, drag the new instance icon(the little blue triangle) to the desk top. This of course creates another instance of DynamicCrop with the same setting as those you will use on the RGB image. Now, execute the original instance of the crop tool on the  RGB image and then cancel(red X) that instance. Then make the luminance image active and open the new instance of the Dynamic Crop that you saved to the desk top. That will give you the same crop dimensions for your L image as you already used on the RGB. Execute this instance for the L image. Now, both images will be cropped, have the same dimensions and remain registered to each other.

Steve

[mcbbcn]

Very cool! There are so many ways to skin a cat...

[jtheios]

I normally use exactly Miguel's technique. Sometimes I even create the Dynamic Crop process before creating the RBG image (using Channel Combination). It's often easier to determine the exact area to crop on a single master color image or even the luminance image.

-- John

[mcbbcn]

Hi,

Yes, I ended up using dynamic crop and then star align with RGB as a reference, and it created the right proportions for the luminance.  It still added a black edge at the left side of the luminance picture, but DBE did not seem to have any problems calibrating the gradients using the same points that I had use for the RGB.  Some of the gradient points ended up in the black edge, but it did not seem to affect the removal of gradients int the luminance, so everything workout great.

Thanks everybody for your help,

Miquel