Mosaic Question

[shammo]

Hello Folks,
I am putting together a 4 frame mosaic of the Andromeda galaxy. The luminance was easy enough because I didn't need to worry about color matching. Here is my question:
Are there any processing steps that should be accomplished to the individual rgb frames before I join them together? Like DBE or background neutralization, etc. Or, should I just combine the rgb's for each frame and then join them using the mosaic tool in Star Alignment,  then do the processing?

Thanks,
Scott

[pfile]

you should strive to get each frame as gradient-free as possible. as for RGB combine before or after mosaic, i'm not sure. certainly working with greyscale images during the mosaic creation (and gradientsmergemosaic) is probably easier.

rob

[shammo]

Thanks Rob. I will continue to play around for the best option.

Scott

[shammo]

Rob,
Are you suggesting that I do the 4 frame combine of the reds, remove the gradients, then combine the 4 frames of the green, etc…? Then do the rgb combine? That seems like the best solution, then run star alignment before the rgb combine.

I will look at this as an option as well. Thanks,

Scot

[pfile]

well both paths are possible. i've only done mono mosaics so i am not sure what really works in practice.

if you make a reference mosaic and then create the R, G and B mosaics against the reference, then all the mosaic'd images should line up perfectly with one another.

if you instead make 3 separate mosaics by building them up separately piece by piece, there's probably some risk that the final mosaics won't line up on one another properly.

doing the RGB combine first (meaning, making a bunch of RGB images first, then creating the mosaic from them) is definitely safer as in the end you only need to create one mosaic (though in order to use GradientsMergeMosaic you still have to make a reference mosaic.)

i have not run GMM on color images but i suppose it should work. Georg will have to chime in.

rob

[georg.viehoever]

GMM on RGB images should work, it simply merges all 3 channels seperately.
Georg

[chris.bailey]

Ive only done it in Narrowband but I made Ha, SII and OII mosaics first and then did the Pixelmath thing. Meant I could play with different blends for the whole image.Key things for me were using DBE on the individual panes paying particular care with the boundaries, cropping off so no bright stars sat close the merges and using distortion correction. I have also done it with a synthetic star field created for the end mosiac and registering all stacked frames against that with distortion correction on. Worked well but means you have to deal with a lot of big images all the time.

[shammo]

Thanks for the feedback. I had to do a little research to discover exactly what GMM was and found Harry's tutorial. I will look these options over guys and post a result in a few days. Life is getting in the way of my processing…..

Scott