I was looking at Rob Gendler's page wher he talked about merging H Alpha data into red frames as a way of adding the contrast inherent in a good Haplha image. Is there a way to do this in CCD Stack?

Probably the most important aspect of H-a enhanced color is that the red frame must be modified in order to avoid the “pink” or gray nebula that results from using an H-a Lum on top of a normal RGB. The pink/gray coloration occurs because the RGB exps are often weak (due to sky glow) and the H-a areas actually contains more than just red H-a (although that’s all the H-a lum is sensitive to). So a desirable modification of the red frame is to add-in some H-a nebula signal while not disturbing the stars (otherwise the star colors will become distorted and ugly halos may also result).

There are several ways to use CCDStack for merging (or subtracting) data from different filters. For the most part, CCDStack tools and procedures are straight-forward math and can be easily conceptualized. CCDStack implements two basic ways of combining different images – “Combine” and “File Math”, which can be used with “Pixel Math” to prepare individual frames.

File Math consists of simple addition/subtraction and multiplication/division. The relative strengths of the operands can be controlled via “pixel math”. For example, if you want to subtract a red frame from an H-a frame to remove the stars, then 1) measure the star fluxes in each frame; 2) use pixel math to multiply or divide one of the frames so that the star fluxes are as nearly identical as possible; 3) use “file math” to subtract the red from the H-a. Or, to pump-up a red frame with H-a data: 1) measure the red star fluxes; 2) use file math to add the H-a and Red (use pixel math to scale the H-a co control the relative contribution); 3) re-measure the fluxes in the combined image and then multiply/divide via pixel math to restore the original fluxes. This results in a red frame that preserves star colors while emphasizing H-a features (though this method is unnecessarily more work that the “max combine” method discussed below).

The “Combine” methods offer even more flexibility and are potentially easier to use. The max combine is especially useful for H-a/Red combine. Max combine means that at each location the brightest pixel of the stack is chosen for the resulting image. So in a red/H-a max combine, the stars will come from the Red (they are brighter thru the broader filter) while the nebula areas in the H-a image dominate over the Red frame (assuming that the H-a frame is appropriately pre-scaled via pixel math). The new red frame preserves star colors while enhancing H-a features.

Further flexibility is possible by modifying or adjusting the Lum (e.g. it could be simply the H-a or a blend of any or all 4 colors). More exotic processing is possible via non-linear scaling (pixel math or DDP/gamma) and subtractive or multiplicative processing, though such sophistications and complications are usually not all that productive (but they are informative). This forum has some messages regarding these issues and I encourage you to report any methods that you develop.

Stan

Okay, I went looking for my Halpha data but I think it went on walkabout with the latop that got stolen. I'll have to wait for next year to get the H aplaha data. on the rosette which was my target of interest