Messier 33: An Icon

OTA: CDK17
Camera: FLI Proline 16803, 9 micron pixels, 0.64 arcsec/pxl
Observatory: Rodeo, NM (Bernard Miller)

EXPOSURES:
R: 16 x 900 seconds
G: 16 x 900
B: 16 x 900
L: 26 x 1200
H: 16 x 1800
Total exposure    28.5 hours

Image Width: 42 arc-minutes
Processed by Alex Woronow (2022) using PixInsight, Topaz, SWT, NbA

There is not much left to say about Messier 33 that both professional and amateur astronomers have not already said, so I will note some details about my image and the processing that went into it.


The most prominent feature of M 33 is the number of large, bright red hydrogen-alpha clouds. My processing primarily focused on extracting their details and textures. This endeavor started by using a script I wrote (NbA) that extracts the emission lines (just Ha, in this case) from the emission line plus continuum that the narrowband filer captures. (Send me a note through Astrobin if you want a copy of the PI Script.) The 2x extracted line augmented the red channel of the RGB image. The image was then photometrically color calibrated, based on star colors, and stretched using only histogram and curves adjustments.


Aside: I did not use the L subs. I have encountered images where adding the L appears to degrade the final resolution. I know, “our eyes see more detail in gray than in color.” But every color pixel contains a luminance-value equivalent already (at just the right level for the hue), and it is easy to show that adding L to an RGB image causes the hues to shift. I did not want the hues to shift, and my comparison of the with-L and the without-L images revealed no advantage to the former.


The resulting image was taken into Topaz Studio2 for improvements in clarity and noise and then returned to PI for star removal. Then back to TS2 for operations on the starless image, including improvements in color contrast, sharpness, and dehazing. The starless image was again returned to PI, where it was cropped and saved (and presented here). PI also provided the platform for re-introducing the stars into the image via Bill Blanshen’s excellent tool. (Nothing else does as well, including unscreening and re-screening, which is a “blending mode” and not what we want if we are after retaining our color calibration.) That restarred image appears above when there is a mouse-over.


The Elegant Crab Spider, which I published here: https://astrob.in/h89tv0/0/, appears toward the lower left of the galaxy.  

I hope you enjoy the image…
Alex Woronow