Image Processing Questions

The attached image is 4 CS2 screen shots of my initial image processing steps for M51. In the first shot, I've opened a single fits frame in the Fits Liberator Plugin for Photoshop. The default shows the linear stretch function and the histogram is slewed far left.

The second shot shows my first adjustment by changing the stretch fuction to Log(x) which places the histogram in the center of the scale. My first question is what is happening to the histogram on the left side causing the comb efect?

In the third shot, I've repositioned the black and white point sliders to the ends of the histogram curve making sure to stay within the solid part of the curve. I'm assuming the the comb effect is data loss or no data.

The fourth image shows the resultant frame after I've closed the Fits Liberator. After this, I take all the resultant images which are now saved as tiffs and align and stack them in either registax or K3CCDTools. K3CCDTools seems to me to do the better job of alignment and stacking so I usually use it.

Each frame exposure was 60 sec with a total of 73 frames taken. After alignment and stacking, I continue to process the result in CS2 by adjusting the gradient, curves, and levels in that order until I arrive at a pleasing image. Most of the time I will revisit curves and levels to increase appeal.

In the following Post, I've included the final processed image of M51. So, does my processing sequence make since? Am I doing this all wrong or out of sequence? Do the histograms point to an error in my data capture other than perhaps under exposing?

Please, some pointers from you experienced imagers.

Thanks Scott

Attached Image:

Here is the resultant image from the previous post processing steps.

Attached Image:

Hi Louis,
I have never used the Fits plug in so I'm not sure what the proper steps would be with it.
Some things that strike me as being out of order with your processing are you did not mention doing any dark subtraction,are you doing this?
This is the first thing I do after looking over all my subs to make sure they are acceptable.

Second thing is stretching all the individual subs before combining them.I think if you align and stack before stretching you should get a smoother result and save yourself a lot of work too!

My workflow goes something like this most of the time.
Open all subs and make sure they are usable.
Do a dark subtraction and flats if you have them on all the subs.
Do a hot and cold pixel removal on all the subs(I sometimes skip this,it takes awhile)
Align all the subs, LRGB if that is what you have.
Stack the aligned and calibrated subs into seperate LRGB stacks.
I don't have a fits plug in so I then convert the stacked LRGB subs into Tiffs for use in Photoshop.
I combine my RGB channels in Photoshop using the merge channels function.
Sometimes I do a DDP stretch on the luminance before converting it to a Tiff.

Now I have my master luminance and RGB stacks,from here I fumble around in photoshop with it's plethora of tools until I get something that looks OK

I am not very experienced and have an awful lot to learn so I may very well be doing something I shouldn't or not doing something I should.

Hope this helps,
Jason