/**
 * @license
 * 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.
 */
/**
 * Utility methods for calculating contrast given two colors, or calculating a
 * color given one color and a contrast ratio.
 *
 * Contrast ratio is calculated using XYZ's Y. When linearized to match human
 * perception, Y becomes HCT's tone and L*a*b*'s' L*. Informally, this is the
 * lightness of a color.
 *
 * Methods refer to tone, T in the the HCT color space.
 * Tone is equivalent to L* in the L*a*b* color space, or L in the LCH color
 * space.
 */
export declare class Contrast {
    /**
     * Returns a contrast ratio, which ranges from 1 to 21.
     *
     * @param toneA Tone between 0 and 100. Values outside will be clamped.
     * @param toneB Tone between 0 and 100. Values outside will be clamped.
     */
    static ratioOfTones(toneA: number, toneB: number): number;
    static ratioOfYs(y1: number, y2: number): number;
    /**
     * Returns a tone >= tone parameter that ensures ratio parameter.
     * Return value is between 0 and 100.
     * Returns -1 if ratio cannot be achieved with tone parameter.
     *
     * @param tone Tone return value must contrast with.
     * Range is 0 to 100. Invalid values will result in -1 being returned.
     * @param ratio Contrast ratio of return value and tone.
     * Range is 1 to 21, invalid values have undefined behavior.
     */
    static lighter(tone: number, ratio: number): number;
    /**
     * Returns a tone <= tone parameter that ensures ratio parameter.
     * Return value is between 0 and 100.
     * Returns -1 if ratio cannot be achieved with tone parameter.
     *
     * @param tone Tone return value must contrast with.
     * Range is 0 to 100. Invalid values will result in -1 being returned.
     * @param ratio Contrast ratio of return value and tone.
     * Range is 1 to 21, invalid values have undefined behavior.
     */
    static darker(tone: number, ratio: number): number;
    /**
     * Returns a tone >= tone parameter that ensures ratio parameter.
     * Return value is between 0 and 100.
     * Returns 100 if ratio cannot be achieved with tone parameter.
     *
     * This method is unsafe because the returned value is guaranteed to be in
     * bounds for tone, i.e. between 0 and 100. However, that value may not reach
     * the ratio with tone. For example, there is no color lighter than T100.
     *
     * @param tone Tone return value must contrast with.
     * Range is 0 to 100. Invalid values will result in 100 being returned.
     * @param ratio Desired contrast ratio of return value and tone parameter.
     * Range is 1 to 21, invalid values have undefined behavior.
     */
    static lighterUnsafe(tone: number, ratio: number): number;
    /**
     * Returns a tone >= tone parameter that ensures ratio parameter.
     * Return value is between 0 and 100.
     * Returns 100 if ratio cannot be achieved with tone parameter.
     *
     * This method is unsafe because the returned value is guaranteed to be in
     * bounds for tone, i.e. between 0 and 100. However, that value may not reach
     * the [ratio with [tone]. For example, there is no color darker than T0.
     *
     * @param tone Tone return value must contrast with.
     * Range is 0 to 100. Invalid values will result in 0 being returned.
     * @param ratio Desired contrast ratio of return value and tone parameter.
     * Range is 1 to 21, invalid values have undefined behavior.
     */
    static darkerUnsafe(tone: number, ratio: number): number;
}