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Add mode and 32 bit
Add, screen, color dodge and linear dodge don’t seem to work correctly in AE CS6’s 32 bit. These modes can all make an image darker or even black. If I understand any of these, they should only be able to lighten an image, never darken. To test, take two 50% grey solids, set the top to add mode – the comp’d image is white, correct. Apply levels to the top layer and slide it’s input black point way down. You’ll see the comp’d image get dark until it turns black. Really, ADD is making my image black? Something is very wrong here!
How can this be? Lighten and Lighten color still work normally.
Does anyone know why this would be? -
18 Replies
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Check project settings? This post by Stu Maschwitz is a must read
https://prolost.com/blog/2006/2/7/linear-color-workflow-in-ae7-part-1.html
You should follow me on Twitter here. My latest work
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I’m EMMY Nominated for Boardwalk Empire. There is nothing whacky in my project settings. This is a real problem with AE and it’s math at 32 bit. I’ll read the link, thanks.
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Ok, the link does not address this problem at all. In my experience as a professional working in a “project setting color space” brings in too many variables to be reliable. Like most other professionals who work in AE and log space we use a lut to view our images instead of depending on a project setting.
My problem is that I’ve pulled the highlights out of a bloody wound, darkening everything else then using ADD mode to make it pop. All looks great in 8 or 16 bit, but in float ADD does not work and the whole thing turns black. I’ve had to go to “lighten” which I’m not happy about. I cannot render in 16 bit as these images have ultrabrights to the tune of 1.8+.
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Photoshop does the same thing in 32bit. How can black be “added” to anything and be darker than the original?
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[G. Scott Scribner] “Photoshop does the same thing in 32bit. How can black be “added” to anything and be darker than the original?”
When you add a negative number it’s called subtraction 🙂
Darby Edelen
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it definitely seems like a bug, however it seems to be with levels… experimenting with curves seems to be working as expected.
doh! darby’s right, and curves shows the same thing… (double doh!)
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW -
Sorry, here’s a more helpful bit of info. Try turning the Clip Output Black property to “On” at least for the top layer.
Darby Edelen
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Yep, once you go to 32 bit float you have the possibility of values less than 0. If you are crushing blacks then they are dropping below 0.
This isn’t a bug, it is the way float values work. You just need to be aware of it and clamp values at 0 where needed.
Curves and gamma do even weirder stuff sometimes as they usually pivot around 1 and 0, so you can think you are making everything brighter, but you can actually be darkening your superbrights (at least this happens in Nuke).
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Never mind. I’m an idiot. I forgot about the “clip to output” options in levels. Turn on clipping and all is how it should be.
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[G. Scott Scribner] “Add, screen, color dodge and linear dodge don’t seem to work correctly in AE CS6’s 32 bit. These modes can all make an image darker or even black.”
As Darby and Conrad have pointed out, this behavior you’re seeing with Add (and Linear Dodge, which is kind of Add by another name) is correct because of your use of negative numbers.
I’ll add that mathematically, Screen and Color Dodge both necessarily assume input values between 0 and 1, because they work by inverting one or both of the layers — that is, subtracting the value of the components of a layer from 1. With values above 1 or below 0, inversion is impossible and will give unexpected results, unless you clip. As such, these modes are poor choices for compositing in floating point in any application, unless you clip values. By clipping blacks to 0 and whites to 1, you gain the ability to invert an image (but of course, you lose all that dynamic range, so you may or may not want to do some range compression first and then expansion after the blend).
Lighten never darkens because it uses the maximum value of each of the two input sources’ components, whereas Add can darken because adding a negative number to a positive number does not result in a higher positive number. Likewise, Subtract can actually brighten an image if you’re subtracting negative values.
Basically, working in floating point removes an assumption (that all input values will be between 0 and 1) upon which some blend modes (and the common understanding of what they actually do) rests.
Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
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