Image Filter

Intensity = (R + G + B) / 3

YCbCr

Y = 0.2126*R + 0.7152*G + 0.0722*B

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Blend mode

• https://en.wikipedia.org/wiki/Blend_modes

Here color is between 0.0(black) and 1.0(white).

Normal

$$f(a,b)=b$$

Dissolve

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Multiply

$$f(a,b)=ab$$

Screen

$$f(a,b)=1-(1-a)(1-b)$$

Overlay

$$f(a,b)=\{\begin{array}{ll}2ab& a<0.5\\ 1-2(1-a)(1-b)& a>=0.5\end{array}$$

Hard Light

Soft Light

Dodge and burn

Divide

Addition

Subtract

Difference

Darken Only

Lighten Only

Alpha channel

• Alpha compositing - Wikipedia
• アルファチャンネル - Wikipedia

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Reference

• https://dunnbypaul.net/blends/
• https://stackoverflow.com/questions/15007304/histogram-equalization-not-working-on-color-image-opencv