Author Topic: Blending Modes - Normal vs Passthrough vs Replace  (Read 4073 times)

I was looking at this documentation page again:
https://support.allegorithmic.com/documentation/display/SPDOC/Blending+modes

I just can't get into my tiny little head the difference between Normal, Passthrough, and Replace blending modes.  Maybe that's because the pictures all look the same.

Can someone use different words or more other pictures that help explain the difference?


P.S.
I see the animated GIF demonstrating the "Channel" dropdown.  I remember suggesting that based on a newbie question I had, and after seeing similar animations on other pages.
https://forum.allegorithmic.com/index.php?topic=7500.msg36131#msg36131
Nice job, Allegorithmic, and thanks for listening to newbies as well as experts.  :)
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I guess I can answer that, as I was researching this just a couple of days back  :) If someone knows better, please correct me, as I'm also interested in understanding it to full extent.

So, the Normal is just... normal. Pixels that are above in layer stack displayed on top of ones that are below. If there is no pixels above (empty layer or an empty part of it), then anything that is below is displayed, in the same order - from top to bottom.

Passthrough is a tricky one :) I'm not sure that I understanded it correctly, but in simple words to me it looks like this blending mode makes a layer to kinda "pull" the content of layers below into itself, but keeps this "passthrough" layer independent of others in terms of opacity control and painting abilities. For example, normally you can't paint on a Fill layer, thus can't use the Clone Tool on it. If you add a Paint effect to this Fill layer or a regular layer (non-Fill) just above it, you can paint in it over your Fill layer, but still can't use the Clone Tool, because the layer itself doesn't contain the information you need (no pixels from a Fill layer are there). But, if you set the layer above to Passthrough, the content of Fill layer below is "pulled" above, and now you can use the Clone Tool (on regular layer above the Fill). Also you can notice how thumbnail of the layer updates when you set it to Passthrough - it starts to represent the computed result of layer stack below ("pulls" the content inside itself).

Replace is pretty simple — it completely replaces the content of all layers that are below with content of the layer itself, including the parts that are empty. In a sense, setting a layer blend mode to Replace will make it look like there is no other layers below. For example, if you have a layer stack full of data and a layer with a single pixel on the very top of it, setting this top layer blend mode to Replace will make only this one pixel visible, while the content of the layers below will be discarded completely.

Hope that helps :) Oh, and I would like to add one more question to this topic. Could anyone kindly explain what's the practical difference between AddSub and Linear Light modes in Painter? From what I learned, I would assume they should produce identical results. Maybe there are some specific cases when one of them should be used and other one shouldn't? Thanks in advance.
Last Edit: April 20, 2016, 07:39:14 am

Hey!  Thanks a lot!   :D

Your explanations were great and I was able to understand what you were saying.

I'll have to play with them some now and try to predict the results.  If successful, then I'll know I really got it.  The greatest challenge might be to remember it for more than 2 minutes, but my "prediction" exercise should help a lot.

Thanks again.
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