Colour image from a mono CCD?

[Alien]

Sorry if this sounds obvious to some but how can you make a colour image using a mono CCD?

I have read that the most sensitive cameras are mono CCD, which makes perfect sense. Also, people built composite images by recording AVI files through RGB filters, then overlay them in Registax - but this is still a mono composite image, is it not?

What I don't understand is how you go from the RGB filtered mono images to a single colour image. I assume that the filtered RGB mono images have colour added in photoshop or similar, and that this can be achieved more accurately if the mono images are first filtered.

[jgs001]

I'm not sure on the process, as I've not done it myself, but you create an image from each of the colour filtered avi's/image stacks. One of R G and B. Then you combine them in an editing program, by putting the R filtered image in the R channel, the G in the green, and the B in the blue. This creates a composited image in full colour. No colour is added at this point, but I guess, if it suits, the saturation can be boosted to bring out more colour.

[NickH]

Yes, basically most of the colour images you see here taken with mono cameras, the individual will use a filter wheel, and rotate it after each colour is "done"

Usually, I will go with a Hydrogen Alpha filter for the Luminance data as this will typically give you a nice crisp image for the "light" part ,and then, using software, blend in the red green and blue channels. Software like Maxim DL, will handle the alignment and colour compositing very well as well as balancing the channels out.

[MartinB]

As Nick says except the hydorgen alpha is only of use as a luminence with emission nebulae.

You will frequently see the letters LRGB used when colour images have been produced using a mono CCD. The L stands for luminence and is normally taken without any colour filtration. The luminence is processed as a monochrome image. The images produced with the RGB filters are, of course, still mono. Software converts them to there individual colours and combines them to produce a tricolour image. Photoshop can do this very well as can other packages.

The luminence image is then applied to the RGB image. The eye can detect detail (luminence) hue, saturation and colour (RGB). So the luminence channel can add greatly to the clarity of the image allowing less time to be spent collecting colour data.

LRGB is a much simpler process than it sounds but it's proper application is debated quite fiercely!

Here is a primer I wrote some time ago. There are parts I would modify if writing again e.g. some of the comments about binning but I think it works as an introduction

LRGB imaging

[NickH]

Yup, as Martin says...

With Galaxies etc....I tend to use either CLS or some other good lum filter

nice primer too Martin