luminans Mask

[Morten Lerager]

Hi Astroart
Im trying to get rid of other tools than AA8
When i process, some time I need a "luminans mask".
Easy done in GIMP. But I want to stay in AA8.
I cant use the Mask tool i gess.
So maybe turn a color pic. Into a luminans version. And save as PNG to be loaded as Mask.
What's the most correct and easy way

[fabdev]

Hi, in general to create a mask from an image:

1) Create a duplicate of the image (for color images use Luminance).
2) On the duplicate, click Histogram stretch, move the sliders/curves to obtain the desired result, then Apply then OK.
3) On the duplicate, apply filters if needed.
4) Select the original image and click menu "Mask <- Image".

Point (4) creates a mask from another image with 16 bit dynamic, where white is full mask (full processing) and black is no mask (no processing) and the gray values are in-between.
Point (3) let you tune the "mask" (which is still an image).
Hope this helps, Fabio.

[Morten Lerager]

Jep,
It's convert automatic RGB to a Luminans so it's easy to use it as a mask.
I have found the command I was looking for..
With a color image > color > Luminance.
I can use most of the color command with mask.
But not the white balance.. Not that I need it, but where to find what is mask sensitive and what's not?
Thank you Fabio.

[fabdev]

even after Color > Luminance, the Histogram Stretch is needed anyway because the "mask image" must have exactly a 16 bit dynamic. Since the mask image is grayscale, no color filters are possible on it.

[Morten Lerager]

Thank's Fabio
I don't get it I'm afraid.
Sure I don't want to change color in the Mask.
But the Mask is for edit a color pic.
The command color curve works fine with a Mask on it.

"the Histogram Stretch is needed anyway because the "mask image" must have exactly a 16 bit dynamic"

Don't understand why I have to stretch it.
Some times I have done it inside gimp if I want the Mask going from pitch Black to bright white.
But often a gray scale is fine.

Even a total gray Mask all pix. Same Val. Can be used to ajust the effect. And that's not a 16bit dynamic mask.

I might be missing something...

[fabdev]

Hi Morten, OK, I didn't understand well the question. I confirm that White Balance does not work on masks, it works on the full image.

I suggest this: select a mask with the mouse, then Mask->Image, this will create a new image for the mask, notice that the range is 16 bit (0..65535). Process this image (for example a gauss filter), then select the original color image and click Mask<-Image, the mask will be updated.
If you instead need to create the mask from the nebula of an image, then the Histogram Stretch filter on the "mask image" is needed at some point, because you need a linear 16 bit range for the mask.

[Morten Lerager]

Thank you Fabio
Now I can keep on trying making dual band osc picture.