Master Classes 






LRGB Blending

Published 07/04/2018


In this lesson we take a closer look at the techniques used to adjust the blend between Luminance and Color data via LRGBCombination. This step of creating a color image is not typically given much thought and fraught with undesirable results. A generalized model followed by a few examples is shown in this recording.


2023 Comment:

This video was made when ArcSinh stretch was released. After more experience with it, it turns out that that there is also a significant color shift when using this process. So at the end of the day you need to be *very* careful if you use it. In the NGC 3684 Update you can see the example of how to not use ArcSin stretch and still have vibrant (and perhaps even better) results.

See below the video for some additional information. 


Here is the Pixel Math Expression to generate the color bars:


R/K: iif(inrect(x0,y0,width,height),.1,0.02)

G: iif(inrect(x0,y0+300,width,height),.1,0.02) 

B: iif(inrect(x0,y0+600,width,height),.1,0.02)







 If desired, you can download my image that compares the variations of RGB image processing

The expression to create a horizonal gradient is simply X().  This is a function that outputs the horizontal position as normalized value between 0 and 1. So if the x position is  25% across the image (from the left) then the x value is 0.25. Since I am writing this number to the view- it becomes the brightness value. So I will have a range of values from 0 (left side) to 1 (right side)- thus making a horizonal gradient.