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Grokking The Gimp
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5.6.4 The Darken Only and Lighten Only Blending Modes

Darken Only creates a resultant pixel that retains the smallest components of the foreground and background pixels. Thus, if the foreground pixel has the components [r1,g1,b1] and the background has [r2,g2,b2], the resultant pixel is $[\min(r_1,r_2),\min(g_1,g_2),\min(b_1,b_2)]$. This is expressed more compactly as

\begin{displaymath}R=\min\{F,B\}
\end{displaymath}

where $\min$ means component-wise minimization. Not surprisingly, Darken Only mode makes an image darker.

Figure  5.19(a)

  
Figure 5.19: An Example of Darken Only and Lighten Only Modes
Figure 5.19

illustrates the use of Darken Only mode on the flower image from Figure  5.15(a). Because the grayscale layer below the flower is uniformly 127R 127G 127B, everything in the flower that has an RGB component darker than 127 retains its character in the image. The parts of the flower image that are lighter are replaced by the flat gray.

Lighten Only mode has the opposite action of Darken Only. It selects the maximum of each component from the foreground and background pixels. The mathematical expression for Lighten Only is

\begin{displaymath}R=\max\{F,B\}.
\end{displaymath}

where $\max$ means component-wise maximization. Lighten Only mode makes an image lighter.

Figure  5.19(b) illustrates the use of Lighten Only mode on the flower image from Figure  5.15(a). Now, everything in the flower that has an RGB component lighter than 127 retains its character in the image. The parts of the flower image that are darker are replaced by the flat gray.

Grokking The Gimp
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