First attemp at color

[Mack Julian]

Here is my first color image, M57. I mostly to variable star photometry and wanted to mess around with taking a color image. This is 180"x5 ( all unguided ) through each filter. Straight 1:1:1 weights, never got around to running Bobs new script.

Need to learn how to get rid of those weird colored pixels or artifacts from combining images. I used the trial version of CCD stack for this image. Really no clue to what all it can do.

Mack

[Jim McMillan]

Hi Mack,

Very nice. Can I give a few suggestions?

1) CCDStack is a very powerful program. However, I don't find it particularly intuitive. The only way I figured out how to use it is to invest a fair amount of time with the tutorials. In my view, for your first foray into color processing, I think MaxIm is the easier way.

2) The color spots are almost surely hot pixels. The simpliest way to get rid of them is to use MaxIm's "hot" & "dead" pixel filter on each image. You may have to play with the threshold %. You want it to be strong enough to eliminate the bad pixels but not so strong that it affects real data. Mine are set to 2.5%. You can easily automate this process using MaxIm's batch processing window.

3) DDP processing in MaxIm is a pretty good way to do a non-linear stretch. Don't stretch the R,G,B combined images separately. Do it after combining into an RGB. (Having said that, if doing an LRGB, stretching the L separately usually works well.) Fiddle with the background adu setting so the result doesn't cut out any data. Usually that means reducing it about 15 - 30 adu from the auto setting. The spread between the background and mid-level setting determines how strong the non-linear stretch is. The smaller the difference, the stronger the stretch. A difference of 300 adu is usually about as strong as you'd want. The auto setting is usually pretty good.

4) I don't use any of DDP's sharpening. I find I prefer to sharpen (unsharp mask) before using DDP. That seems to minimize any bad effects from sharpening on the stars - particularly after stretching via DDP.

I hope these suggestions make sense.

Regards,

Jim

[Mack Julian]

Thanks for the tips Jim! I'll give your advise a try.

[Taimur Khan]

Its a nice first color! I will second what Jim said.

[Dick Berg]

Mack,

Great work for your very first! Yep, hot pixels in one of the color band images will give you a bright pixel in that color in the final image. You have to have identically-placed dead pixels in two color band images order to raise a "hot pixel" in the third color, and that's not really likely.