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Originally I thought that I could not take color images since my observatory is located in the city and subject to both local and regional light pollution. At AIC 2011 Don Goldman convinced me that it was possible. The city lights are still a problem. The luminance exposure is limited to 420 seconds. Even at that short exposure there is a significant gradient to remove with DBE. While longer exposures are possible with the color filters I have limited them to 300 secs. The Blue filter had a significant gradient. H alpha exposures were set at my standard 900 seconds.
For More infomation
click on the images below for a larger image
The image uses the Luminance filter
to describe the brightness of the image. The Red, Green,
and Blue filters are combined to form a RGB image.
While this image looks like the final, it is of lower
quality. After processing the RGB image is used as the
Chrominance (color) to supply color to the Luminance
Image. This results in the image above.
LRGB Image enhanced with H Alpha
In this image the Red channel is
enhanced by adding a portion of the H alpha signal. See
below for more details.
The RGB image was formed by combining images taken with each color filter using HDR techniques. I used HDR because the bright stars were saturating in my test shots. Since I want well colored stars, I shot short duration exposures and then combined them with HDR Composition.
There are really not enough of the long exposure images. Originally I was taking 600 second shots, but after more study I decided that 300 sec shots would be enough. Unfortunately I ran out of time (and good weather) as M33 is not setting into my trees rather early.
The H alpha image is a rather straightforward combination of 40 900 second exposures. Since I was also testing the effects of the moon some of the exposures had gradient due to being shot too close to the moon.
For the LRGBH image I used the technique described by Harry's Astro Shed. In my case I got better results by using the finished images instead of working the linear image. Harry's technique is to create a scaled intermediate of the Ha image and then combine that image to form the final "Rh" image.
The Luminance was 43 exposures of 420 seconds each. Since I do not have a rotator I DBE'd each sub exposure to remove the gradient caused by local light pollution. The result was a fairly clean image
All of these images were processed using the new PixInsight 1.7 Gradient, HDRMultiScaleTransform, and MultiscaleMedianTranform functions
Last year M33 was one of the first astrophotography projects I attempted at the observatory. Aside from this being a color project and the 2010 project being grayscale, this time I used the FSQ 106 and have the mount better tuned for good tracking.