Contrast Negate blend mode (still puzzling it)

[dmstraker]

Still trying to figure out Contrast Negate. Would love for some kind and clever person to tell me what the algorithm is.

Latest nugget: Duplicate layer. Add Curves to bottom layer. Pull left node all the way up and the right node all the way down. You now have the original image. Indeed, if you take an image and just do the curves inversion on it, the result looks like a Contrast Negate.

So is it something to do with inverting the luminance?

[Callum]

Hi Dmstraker,

 

I have spoken to James (the lovely voice behind our tutorials) and he has informed me that Contrast Negate is used for text. As it will make the colour of the text contrast the colour of the object behind it to ensure the text is legible you can find an example below  

 

Thanks

Callum

[dmstraker]

Thanks, Callum (and James). Very helpful.

Still curious about the algorithm it uses...

[jenkm]

If blend color Luminosity > 50% then:

 

All pixels with Luminosity values less 50% are replaced by the blend color,

and the pixels with Luminosity greater 50% are replaced by inverted blend color.

 

If blend color Luminosity < 50% then opposite:

 

All pixels with Luminosity values less 50% are replaced by the inverted blend color, 

and the pixels with Luminosity greater 50% are replaced by blend color.

 

So this Contrast Negate mode is some kind of two-tone Posterization.