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# Multiply effect.

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well im trying to make a program in vb.net and i would like to know if anybody here know how does the efect multiply works.

tty for the help

gooden

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Paint.NET is open-source. Look for it on getpaint.net - you can download and take a look yourself :-)

So you know: Multiply isn't an effect, per se. It's actually a layer blend mode. That should help you find it.

The Doctor: There was a goblin, or a trickster, or a warrior... A nameless, terrible thing, soaked in the blood of a billion galaxies. The most feared being in all the cosmos. And nothing could stop it, or hold it, or reason with it. One day it would just drop out of the sky and tear down your world.
Amy: But how did it end up in there?
The Doctor: You know fairy tales. A good wizard tricked it.
River Song: I hate good wizards in fairy tales; they always turn out to be him.

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The multiply blend mode has a big hint in its name as to how it works.

For each pixel, each color channel's value for the layer set to multiply is multiplied by the value of the pixel in the layer below it (or in the resulting value of the layers below it, since they may also be using different blend modes). The result is divided by a constant value (typically whatever the maximum value possible for each channel is).

So, white (255,255,255 in RGB) in a pixel set to multiply mode atop a blue (0,0,255) pixel would yield:

red - 255 x 0 / 255 = 0

green - 255 x 0 / 255 = 0

blue - 255 x 255 / 255 = 255

...or blue - 0,0,255 (so there would be no change)

cyan (0,255,255) multiplied with yellow (255,255,0) would yield:

red - 0 x 255 / 255 = 0

green - 255 x 255 / 255 = 255

blue - 255 x 0 / 255 = 0

...or green - 0,255,0

Examples at mid-level values are a bit easier to understand if you use a shade of grey (where R, G, and B are equal)

A mid-level grey (127,127,127) in a pixel with mode set to multiply set atop a magenta pixel (255,0,255) would yield:

red - 127 x 255 / 255 = 127

green - 127 x 0 / 255 = 0

blue - 127 x 255 / 255 = 127

...or purple - 127,0,127

More generally explained, darker pixels will darken the underlying layer (or lesser values for a particular color channel will lessen the intensity of that channel), and white will leave the underlying layer unchanged (or max values for a particular color channel will leave the intensity of that channel unchanged).

I have the beginnings of a primer on multiply and additive blend modes (including the underlying math I went through just now) -->here<-- that includes some example images.

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