Purple haze!

[alanrock]

OK, another newbie question. How come when I debayer one of my subs, it comes out with this awful purple tint, and other than this, there seems to be no other color information in the file? When I debayer it in Maxim (Color convert), it looks just fine and you can see actual colors in the galaxy itself. I know my mosaic setting is correct. I suspect whatever is causing this is also contributing to my other issues.

[RickS]

Try an unlinked screen stretch (unclick the little chain icon at top left on the ScreenTransferFunction process.)  That will give you a better representation of the data by stretching the colour channels independently.  Don't forget that the channels are unlinked.  You'll probably want to link them again once you've neutralized the background:

To process the colour data further you're going to need to equalise the background.  There are at least a couple of options for doing this.  If there are no gradients to remove then just use BackgroundNeutralization.  If you have gradients then use DBE.  You can use BackgroundNeutralizaton afterwards but it usually isn't necessary.  Follow that with some form of colour calibration (ColorCalibration or PhotometricColorCalibration.)

The colour is often fairly weak at this stage.  After stretching the colour data you can apply a clipped lightness mask and bump up the saturation with CurvesTransformation.

Cheers,
Rick.

[alanrock]

Thanks! That works just fine. Now I just I have to see if I can wring some color out of the image after I stretch it. I'll do some research on clipped lightness mask!
Alan

[RickS]

Optional step: apply RGBWorkingSpace with R, G & B at 1:1:1 to colour image.  Now extract Lightness (CIE L*) using ChannelExtraction or the equivalent button on the main menu.  Use HistogramTransformation to clip the blacks to taste.  Apply mask to colour image...

The idea is that the mask exposes the bright areas of the image, where you want to boost the saturation, and protects the dim parts.

[alanrock]

I have no idea how to use that tool--when I select the view, it resets the RGB values to whatever it's seeing in the image. There's no documentation for that tool, either!

[RickS]

Just drag the Red, Green & Blue sliders to 1 and apply to the target image using the new instance triangle.  You won't see any visible effect, but it does change the RGB working space of the image so that red, green and blue make an equal contribution to the Lightness that you extract.  I prefer this to the default RGBWS which will favour green by a large factor.