Merge "Update gainmap documentation." into udc-dev

 * 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 {