How is the "Overlay" Blend Function working (Algorithm)?

[IceCave]

I am trying to wrap my head around it, but I can't find a function that blends these colors

(122, 141, 153)

and

(0, 0, 0)

 

into this one

(0, 27, 51)

Edited December 17, 2019 by IceCave

[toe_head2001]

Here's the function for Overlay blend, with your example values:

ColorBgra lhs = ColorBgra.FromBgr(153, 141, 122);
ColorBgra rhs = ColorBgra.FromBgr(0, 0, 0);

byte r = lhs.R < 128
    ? Int32Util.ClampToByte(2 * rhs.R * lhs.R / byte.MaxValue)
    : Int32Util.ClampToByte(byte.MaxValue - 2 * (byte.MaxValue - rhs.R) * (byte.MaxValue - lhs.R) / byte.MaxValue);

byte g = lhs.G < 128
    ? Int32Util.ClampToByte(2 * rhs.G * lhs.G / byte.MaxValue)
    : Int32Util.ClampToByte(byte.MaxValue - 2 * (byte.MaxValue - rhs.G) * (byte.MaxValue - lhs.G) / byte.MaxValue);

byte b = lhs.B < 128
    ? Int32Util.ClampToByte(2 * rhs.B * lhs.B / byte.MaxValue)
    : Int32Util.ClampToByte(byte.MaxValue - 2 * (byte.MaxValue - rhs.B) * (byte.MaxValue - lhs.B) / byte.MaxValue);

ColorBgra overlayColor = ColorBgra.FromBgr(b, g, r);

 

More here:

https://github.com/toehead2001/pdn-blendmodes-plus/blob/master/BlendModesPlus/EffectPlugin.cs#L589

[IceCave]

So it takes the destination color in order to decide between Screen and Overlay and not the source color. Interesting.

Thank you very much. Very helpful.

[toe_head2001]

2 minutes ago, IceCave said:

So it takes the destination color in order to decide between Screen and Overlay and not the source color.

 

Well, you decide which color is the source and which is the destination.

 

The Screen blend mode uses a totally different algorithm, and is not involved in the code I posted.

[IceCave]

Well, yeah, true... anyone finding this topic over Google:

rhs is the pixel color of the top layer (the one set to overlay)

lhs is the blend color of the bottom layers

 

17 minutes ago, toe_head2001 said:

The Screen blend mode uses a totally different algorithm, and is not involved in the code I posted.

I was referring to the documentation, I haven't actually checked

https://www.getpaint.net/doc/latest/BlendModes.html#16

Edited December 17, 2019 by IceCave

[Reptillian]

For the float version of the overlay blending mode formula -

 

a-base

b-blend

f(a,b)= a<.5 ? 2ab : 1-2(1-a)(1-b) ;

 

This implies that the ranges has to be normalized to 0-1 ranges before calculation.

Edited December 17, 2019 by Reptillian