Amazon VERSION 2.0V1 Uživatelská příručka stáhnout pdf (Strana 254)

254

Control (UI) Default Value Function

operation (continued) The available operations (based on the Porter & Duff paper) are:

• ImageAtop - Fb+B(1-f). This shows the shape of the

background, with the foreground covering the background

where the images overlap.

• ImageAverage - (F+B)/2. This produces the average of the

two images. The result is darker than the original images, but

accentuates highlights.

• ImageDifference - abs(F-B). This shows how much the pixels

differ and is useful for comparing two very similar images.

• ImageDivide - B/F. This divides the background values by the

foreground values.

• ImageExclusion - F+B-2FB. This is a more photographic form

of ImageDifference.

• ImageFrom - F-B. This subtracts the background from the

foreground. For subtracting the foreground from the

background instead, see ImageMinus.

• ImageGeometric - 2FB/(F+B). This is another way of

averaging two images. Visually, it's close to ImageMin.

• ImageHypot - sqrt(F*F+B*B). This resembles the ImageAdd

and ImageScreen operations. The result is not as bright as

ImageAdd, but brighter than ImageScreen. ImageHypot

works with values above 1. It can be is useful for adding

reflections, as an alternative to ImageScreen.

• ImageIn - Bf. This only shows the areas of the background

that overlap with the alpha of the foreground. It can be useful

for combining mattes.

• ImageMatte - Ff*B(1-f). This is a premultiplied ImageOver.

Use unpremultiplied images with this operation.

• ImageMax - max(F,B). This takes the maximum values of both

images. This is a good way to combine mattes and useful for

bringing aspects like bright hair detail through.

4 NODES I-K | IMAGESCREEN

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Amazon VERSION 2.0V1 Uživatelská příručka Strana 254