The overlay modes (Overlay, Soft Light, Hard Light, Vivid Light, and Linear Light) are the various blending modes in which the following occurs:
1) A value lighter than 50% gray blended into the source layer or channel will cause lightening to occur
2) A value darker the 50% gray blended into the source layer or channel will cause darkening to occur.
3) A 50% gray will exhibit no change.
Think, for instance, of the effect of a High Pass filtered layer set to Overlay mode above a source image.
Rick Gordon
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On 12/13/07 at 12:46 AM -0800, Marco Ugolini wrote in a message entitled
"Re: notches on the L*axis":
>In a message dated 12/12/07 12:34 PM, Rick Gordon wrote:
>
>> If 50% is not fully quantifiable in 8-bit calculations, then why do we not see
>> degradation of complete neutrality in the a and b channels in Lab, or why do
>> we not see luminosity changes when layering a 50% gray in any of the overlay
> > modes (Overlay, Soft Light, Hard Light, Vivid Light, and Linear Light)?
>
>As for the rest of your question (the part not about L*a*b*), I frankly have
>no idea what you are attempting to ask, and it would help if you clarified.
--
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RICK GORDON
EMERALD VALLEY GRAPHICS AND CONSULTING
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