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Update gainmap documentation.

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Fix formula for W.

Update names in the comments to match Android names.

Remove references to HDR base images (didn't make the cut).

Bug: 266628247
Change-Id: Ice5250dd18ed8255503f1b4c9b6d933d2472990e
This commit is contained in:
Christopher Cameron
2023-03-02 11:12:26 +00:00
committed by John Reck
parent 6c31e64588
commit 7b7ea42ae6
1 changed files with 6 additions and 6 deletions
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12
graphics/java/android/graphics/Gainmap.java
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@@ -63,20 +63,20 @@ import libcore.util.NativeAllocationRegistry;
* as follows:
*
* First, let W be a weight parameter determining how much the gainmap will be applied.
* W = clamp((log(H) - log(displayRatioHdr)) /
* (log(displayRatioHdr) - log(displayRatioSdr), 0, 1)
* W = clamp((log(H) - log(minDisplayRatioForHdrTransition)) /
* (log(displayRatioForFullHdr) - log(minDisplayRatioForHdrTransition), 0, 1)
*
* Next, let L be the gainmap value in log space. We compute this from the value G that was
* sampled from the texture as follows:
* L = mix(log(gainmapRatioMin), log(gainmapRatioMax), pow(G, gainmapGamma))
* L = mix(log(ratioMin), log(ratioMax), pow(G, gamma))
*
* Finally, apply the gainmap to compute D, the displayed pixel. If the base image is SDR then
* compute:
* D = (B + epsilonSdr) * exp(L * W) - epsilonHdr
* If the base image is HDR then compute:
* D = (B + epsilonHdr) * exp(L * (W - 1)) - epsilonSdr
*
* In the above math, log() is a natural logarithm and exp() is natural exponentiation.
* In the above math, log() is a natural logarithm and exp() is natural exponentiation. The base
* for these functions cancels out and does not affect the result, so other bases may be used
* if preferred.
*/
public final class Gainmap implements Parcelable {