chromium/third_party/material_color_utilities/src/cpp/cam/hct.h

/*
 * Copyright 2022 Google LLC
 *
 * 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.
 */

#ifndef CPP_CAM_HCT_H_
#define CPP_CAM_HCT_H_

#include "cpp/utils/utils.h"

namespace material_color_utilities {

/**
 * HCT: hue, chroma, and tone.
 *
 * A color system built using CAM16 hue and chroma, and L* (lightness) from
 * the L*a*b* color space, providing a perceptually accurate
 * color measurement system that can also accurately render what colors
 * will appear as in different lighting environments.
 *
 * Using L* creates a link between the color system, contrast, and thus
 * accessibility. Contrast ratio depends on relative luminance, or Y in the XYZ
 * color space. L*, or perceptual luminance can be calculated from Y.
 *
 * Unlike Y, L* is linear to human perception, allowing trivial creation of
 * accurate color tones.
 *
 * Unlike contrast ratio, measuring contrast in L* is linear, and simple to
 * calculate. A difference of 40 in HCT tone guarantees a contrast ratio >= 3.0,
 * and a difference of 50 guarantees a contrast ratio >= 4.5.
 */
class Hct { … };

}  // namespace material_color_utilities

#endif  // CPP_CAM_HCT_H_