Screen Blend vs Additive

jeffrey merrill

Hi Adam:

I saw in forum posts that you explained that SXT removes star and some portion of background so when re-combining starless and starry images from SXT, you can use pixelMath and add images together.

In the NGC 1491 videos later you were using screen blend function instead to blend starless image that had been stretched and starry images..I haven't used Photoshop so not too familiar with Screen blend..and I'm not really sure why Screen Blend here instead of additive? 

jeff

BlockHead

Additive "blend" is used to combine linear images. 

When the images are non-linear you use the screen blending method (which is multiplicative).

I actually explain why in this video:

Maybe I need to explain somewhere again. But I show EXACTLY what screen blending is doing step by step in the video above. 

-the Blockhead