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Blend Layers merge bug?

Posted: 17 Dec 2014, 19:37
by Sewie
Hello dear TVP friends,

I might have stumbled on a rather serious bug, I think: when I use layers in blend mode (multiply, sub, add, etc) and then merge those layers, something strange happens. The layers seem to behave as if a mask in present and cuts off part of the image from the blend layer.

Here is a screenshot:
MultiplyBug_01.jpg
MultiplyBug_01.jpg (51.26 KiB) Viewed 10391 times
There is strange behavior happening not only in Multiply mode but also with most other blend modes; layers get either cut off or their effect entirely disappears when merged. Please check this if you can.

Re: Blend Layers merge bug?

Posted: 17 Dec 2014, 19:54
by furushil
I think this is normal behavior. Your canvas is probably blank (alpha channel) and you are multiplying the blue to "nothing", so nothing comes out at the end.
No pixels are there to be multiplied with.

Re: Blend Layers merge bug?

Posted: 17 Dec 2014, 20:13
by ZigOtto
Sewie wrote:Hello dear TVP friends,

I might have stumbled on a rather serious big, I think: when I use layers in blend mode (multiply, sub, add, etc) and then merge those layers, something strange happens. The layers seem to behave as if a mask in present and cuts off part of the image from the blend layer.
yep, not really a bug to my eyes,
it happens because your Multiplied layer is multiplied over all the layers underneath,
included the BG when existing, here, your BG is apparently set on Color (= white),
if you set it to None, the pre-merged / post-merged layers will display exactly the same thing,
(in your exemple, the blue part out of the yellow area will disapear).

Re: Blend Layers merge bug?

Posted: 17 Dec 2014, 20:55
by Sewie
Thanks guys! That explains it.
The thing is; when I do exactly the same thing in photoshop I get such a different result. Like this when merged:
MultiplyBug_02.jpg
MultiplyBug_02.jpg (47.35 KiB) Viewed 10377 times
You see, it doesn't clip any layers, so I was expecting the same from TVP. But now that I know why TVP does it this way, I can take it into account.

Re: Blend Layers merge bug?

Posted: 17 Dec 2014, 22:13
by schwarzgrau
Looks like a bug to me too. If the blue is seen before the merge ( already multiplied with a transparent background ) you would expect it to be still seen after the merge.

Re: Blend Layers merge bug?

Posted: 18 Dec 2014, 08:47
by Sewie
Well, I would prefer to have the merged layers not clip any artwork. Because this means that I am forced to merge my layers with a solid color underneath.
If I could keep the properties of the blend layers exactly the way they were before they were merged, it would give me a lot more flexibility.

Re: Blend Layers merge bug?

Posted: 17 Feb 2015, 17:10
by Peter Wassink
the Issue Michael started this thread for, is maybe linked with this issue... when exporting images with layers set in blendmodes (other then color)

i just had this issue:
I wanted to export a yellow line drawing with alpha channel, that is on a layer set to blendmode shade.
in my project view this drawing looks as if it has black lines. but after export i get the original yellow line color.

i could off course recolor the lines and export in colormode.
i'm just wondering about the logic and desirability of the current behaviour.

The advantage of a "what you see is what you get"-behaviour is probably obvious.
but what is the advantage of the current behaviour, i suspect it has to do with some deeper level of logic?