| /* |
| * Copyright (C) 2018 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.android.settingslib.display; |
| |
| import android.util.MathUtils; |
| |
| public class BrightnessUtils { |
| |
| public static final int GAMMA_SPACE_MIN = 0; |
| public static final int GAMMA_SPACE_MAX = 65535; |
| |
| // Hybrid Log Gamma constant values |
| private static final float R = 0.5f; |
| private static final float A = 0.17883277f; |
| private static final float B = 0.28466892f; |
| private static final float C = 0.55991073f; |
| |
| /** |
| * A function for converting from the gamma space that the slider works in to the |
| * linear space that the setting works in. |
| * |
| * The gamma space effectively provides us a way to make linear changes to the slider that |
| * result in linear changes in perception. If we made changes to the slider in the linear space |
| * then we'd see an approximately logarithmic change in perception (c.f. Fechner's Law). |
| * |
| * Internally, this implements the Hybrid Log Gamma electro-optical transfer function, which is |
| * a slight improvement to the typical gamma transfer function for displays whose max |
| * brightness exceeds the 120 nit reference point, but doesn't set a specific reference |
| * brightness like the PQ function does. |
| * |
| * Note that this transfer function is only valid if the display's backlight value is a linear |
| * control. If it's calibrated to be something non-linear, then a different transfer function |
| * should be used. |
| * |
| * @param val The slider value. |
| * @param min The minimum acceptable value for the setting. |
| * @param max The maximum acceptable value for the setting. |
| * @return The corresponding setting value. |
| */ |
| public static final int convertGammaToLinear(int val, int min, int max) { |
| final float normalizedVal = MathUtils.norm(GAMMA_SPACE_MIN, GAMMA_SPACE_MAX, val); |
| final float ret; |
| if (normalizedVal <= R) { |
| ret = MathUtils.sq(normalizedVal / R); |
| } else { |
| ret = MathUtils.exp((normalizedVal - C) / A) + B; |
| } |
| |
| // HLG is normalized to the range [0, 12], so we need to re-normalize to the range [0, 1] |
| // in order to derive the correct setting value. |
| return Math.round(MathUtils.lerp(min, max, ret / 12)); |
| } |
| |
| /** |
| * Version of {@link #convertGammaToLinear} that takes and returns float values. |
| * TODO: brightnessfloat Merge with above method later. |
| * |
| * @param val The slider value. |
| * @param min The minimum acceptable value for the setting. |
| * @param max The maximum acceptable value for the setting. |
| * @return The corresponding setting value. |
| */ |
| public static final float convertGammaToLinearFloat(int val, float min, float max) { |
| final float normalizedVal = MathUtils.norm(GAMMA_SPACE_MIN, GAMMA_SPACE_MAX, val); |
| final float ret; |
| if (normalizedVal <= R) { |
| ret = MathUtils.sq(normalizedVal / R); |
| } else { |
| ret = MathUtils.exp((normalizedVal - C) / A) + B; |
| } |
| |
| // HLG is normalized to the range [0, 12], so we need to re-normalize to the range [0, 1] |
| // in order to derive the correct setting value. |
| return MathUtils.lerp(min, max, ret / 12); |
| } |
| |
| /** |
| * A function for converting from the linear space that the setting works in to the |
| * gamma space that the slider works in. |
| * |
| * The gamma space effectively provides us a way to make linear changes to the slider that |
| * result in linear changes in perception. If we made changes to the slider in the linear space |
| * then we'd see an approximately logarithmic change in perception (c.f. Fechner's Law). |
| * |
| * Internally, this implements the Hybrid Log Gamma opto-electronic transfer function, which is |
| * a slight improvement to the typical gamma transfer function for displays whose max |
| * brightness exceeds the 120 nit reference point, but doesn't set a specific reference |
| * brightness like the PQ function does. |
| * |
| * Note that this transfer function is only valid if the display's backlight value is a linear |
| * control. If it's calibrated to be something non-linear, then a different transfer function |
| * should be used. |
| * |
| * @param val The brightness setting value. |
| * @param min The minimum acceptable value for the setting. |
| * @param max The maximum acceptable value for the setting. |
| * @return The corresponding slider value |
| */ |
| public static final int convertLinearToGamma(int val, int min, int max) { |
| // For some reason, HLG normalizes to the range [0, 12] rather than [0, 1] |
| final float normalizedVal = MathUtils.norm(min, max, val) * 12; |
| final float ret; |
| if (normalizedVal <= 1f) { |
| ret = MathUtils.sqrt(normalizedVal) * R; |
| } else { |
| ret = A * MathUtils.log(normalizedVal - B) + C; |
| } |
| |
| return Math.round(MathUtils.lerp(GAMMA_SPACE_MIN, GAMMA_SPACE_MAX, ret)); |
| } |
| |
| /** |
| * Version of {@link #convertLinearToGamma} that takes float values. |
| * TODO: brightnessfloat merge with above method(?) |
| * @param val The brightness setting value. |
| * @param min The minimum acceptable value for the setting. |
| * @param max The maximum acceptable value for the setting. |
| * @return The corresponding slider value |
| */ |
| public static final int convertLinearToGammaFloat(float val, float min, float max) { |
| // For some reason, HLG normalizes to the range [0, 12] rather than [0, 1] |
| final float normalizedVal = MathUtils.norm(min, max, val) * 12; |
| final float ret; |
| if (normalizedVal <= 1f) { |
| ret = MathUtils.sqrt(normalizedVal) * R; |
| } else { |
| ret = A * MathUtils.log(normalizedVal - B) + C; |
| } |
| |
| return Math.round(MathUtils.lerp(GAMMA_SPACE_MIN, GAMMA_SPACE_MAX, ret)); |
| } |
| } |