Color Imaging

Color imaging from a light-polluted environment presents many problems. We can no longer just image in the red as we need the full spectrum. My philosophy has always been to take the best mono image and then worry about the color later. As mentioned earlier, virtually all my images are shot through a red filter to reduce light pollution and increase contrast. This passes the red and infrared where light pollution is less prevalent. This has the added benefit, that when I want color, I already have a red frame. All that is needed is the blue one (with IR block). The green is the biggest problem, as this is where light pollution is worst. However, the green image can usually be synthesized by averaging the red and blue (see Figure 9.8). The blue image is inevitably light-polluted and much more noisy than the red. However, using the LRGB method, the red frame is used as both the R and L (luminance) frames, preserving the detail of the black-and-white image and only adding the color from the low-quality color image. MAXIM makes this fairly straightforward.

I have also used the color from my old photographic slides, having an extensive library of color images, which again can provide the low-resolution color information to supplement the high-resolution CCD image (see Figure 9.9). The final processing stage for color images is inevitably that noise-reduction filter again.

Figure 9.13.

Selection from Arp Peculiar Galaxies. 1 - NGC2857 (Arp's Spiral); 6 - NGC2537 (Bear's Paw Galaxy); 25 - NGC2276; 78 - NGC772; 84 - NGC5394/5; 94

- NGC3226/7; 116 -M60/NGC4647; 120

- NGC4435/8; 263 -NGC3239; 270 -NGC3395/6; 319 -NGC7317 (Stephan's Quintet).

Selection from Arp's Atlas of Peculiar Galaxies

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