Color vs. Mono Camera Match SBIG ST-2000XCM color camera vs. the ST-2000XM mono w/filters
The XCM Hybrid
Combine a high resolution XM mono luminance layer with an XCM color layer for big changes
This isn't a test but more a demonstration of a growing trend to use a high resolution, high S/N grayscale luminance layer taken with a mono camera and combining it with a color layer taken with the XCM. I call this the 'XCM Hybrid' technique because it uses two different camera types to accomplish the task. This technique is already widely used with separate L,R,G,B layers taken with a mono camera and is commonly referred to as the "Luminance Layering" method and is one of the major benefits of using a mono camera.
You can use the hybrid technique if you now have a mono camera and want to enhance your previous or new images taken with the XCM. This technique uses lower resolution XCM color layers blended into a high resolution luminance layer taken with the XM to produce high resolution color images. The results are well worth the effort.
Below are examples of NGC 6992 and NGC 7635 the Bubble Nebula before and after a grayscale luminance image taken from the XM camera was added.
Same image above combined with the luminance layer from the XM
No additional processing was performed.
Star edges with jagged artifacts have improved or eliminated.
The finer structure details have improved tremendously.
Three hour image taken with the XCM.
This image has undergone color processing with selective sharpening to the filament structures to match the XM version.
Some jagged star edges can still be seen.
Same image above combined with the luminance layer from the XM.
Three hour image taken with the XM camera.
Only processing was DDP.
No hot or cold pixel repair.
Same image above combined with the luminance layer from the XM.
Even a mono RGB image can use a boost from a Lum layer!
In this case it is commonly referred to as an LRGB image and it one of the benefits of using a mono camera.
XCM Bubble Nebula combined with XM luminance layer.
XM Bubble Nebula.
XM Bubble Nebula combined with XM luminance layer.
The XCM Hybrid Summary
This technique works very well when using a high resolution, high S/N luminance grayscale layer to boost S/N and detail contrast. When using this technique spend more time gathering data for the "L" layer as it will add details that are more difficult to bring out in normal RGB images as well as improve the overall S/N of the image. Creating a synthetic luminance layer from the color XCM image will not contain any improved S/N, brightness or details as the base RGB image and stretching the image more will only raise the noise level that is already there.
The flip side of this method is that if you already own a mono camera and filters then you might as well use filters to collect the color data requiring less time because you can bin the CCD output 2x2 which has the effect of increasing the pixel size and may also improve S/N. Currently you can not bin the XCM as it will destroy the color information. SBIG is working on developing a binnable color camera that will preserve color data and may be released late in 2008. A good set of astronomical filters and filter wheel can be expensive so until you have them then consider the hybrid method as a very effective alternative.
