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"Add" generates a black border - 32-bit linear

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Maria Smith
"Add" generates a black border - 32-bit linear
on Jan 14, 2018 at 2:46:47 pm

When using 32-bit linear workflow and using blending mode "Add", I get black borders around the video that was supposed to blend. Any ideas?
Please have a look at the attached screenshot, or have a look at it here: https://www.dropbox.com/s/m3ql9rawnxwz6st/black_border_32_bit_linear.jpg?dl...



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Simon Ubsdell
Re: "Add" generates a black border - 32-bit linear
on Jan 14, 2018 at 5:00:59 pm

If you add a negative value to a positive value you will get a subtraction.

The chances are that the element you are trying to add has negative values (in the deep blacks at the edges), i.e, pixels that are below zero.

Hence the darkening effect.

Simon Ubsdell
tokyo productions
hawaiki


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Walter Soyka
Re: "Add" generates a black border - 32-bit linear
on Jan 15, 2018 at 9:54:55 am

[Simon Ubsdell] "If you add a negative value to a positive value you will get a subtraction."

Indeed, this is one of the ways that 32bpc floating point works differently than 8bpc/16bpc.

The Levels effect has an option to clamp black and/or white. Add Levels, leave the "normal" Levels controls (the histogram, inputs, gamma and outputs) alone, and change "Clip to output black" from its default "Off for 32bpc color" to "On."

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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