What are the concepts of contrast, hue, saturation, color levels, and color temperature?

1. Contrast

Contrast refers to the measurement of different brightness levels between the brightest white and the darkest black in the light and dark areas of an image. The larger the difference range, the greater the contrast. The larger the value, the smaller the difference range and the smaller the contrast.

Contrast has a very critical impact on visual effects. Generally speaking, the greater the contrast, the clearer and eye-catching the image will be, and the more vivid and colorful the colors will be. However, if the contrast is small, the entire picture will be gray. High contrast is very helpful for image clarity, detail expression, and grayscale expression.

2. Hue

Hue refers to the relative lightness and darkness of an image, which is expressed as color in color images. Hue is the expression of the reflection and radiation energy intensity of ground objects on the image. The properties, geometric shape, distribution range and combination rules of ground objects can all be reflected in remote sensing images through hue differences.

3. Saturation

Saturation refers to the vividness of color, also known as the purity of color. Saturation depends on the ratio of chromatic and achromatic components (grey) in the color. The greater the color component, the greater the saturation; the greater the achromatic component, the smaller the saturation.

Pure colors are highly saturated, such as bright red and bright green. Colors mixed with white, gray or other tones are unsaturated colors, such as purple, pink, yellowish brown, etc. Completely desaturated colors have no hue at all, such as the various grays between black and white.

4. Color scale

Color scale is an index standard that expresses the brightness of an image, which is what we call the color index. In digital image processing tutorials, it refers to grayscale Resolution (also called grayscale resolution or amplitude resolution).

The color richness and fineness of an image are determined by color levels. The color scale refers to brightness and has nothing to do with color, but the brightest is only white, and the least bright is only black.

5. Color temperature

Color temperature is a unit of measurement that represents the color components contained in light. Theoretically, color temperature refers to the color of an absolute black body that is heated from absolute zero (-273°C).

After the black body is heated. Gradually changes from black to red, to yellow, to white, and finally to blue light. When heated to a certain temperature. The spectral components of the light emitted by a black body. It is called the color temperature at this temperature, and the measurement unit is "K" (Kelvin). If the light emitted by a certain light source has the same spectral component as the light emitted by a black body at a certain temperature, it is called a certain K color temperature. .

If the color of the light emitted by a 100 W light bulb is the same as the color of an absolute blackbody at 2527°C, then the color temperature of the light emitted by this light bulb is: (2527+273) K=2800K

Extended information:

Contrast

Contrast refers to the measurement of different brightness levels between the brightest white and the darkest black in the light and dark areas of an image, and the range of differences The larger the contrast ratio, the greater the contrast. The smaller the difference range, the smaller the contrast. A good contrast ratio of 120:1 can easily display vivid and rich colors. When the contrast ratio is as high as 300:1, it can support various levels of color. .

But contrast ratio suffers from the same dilemma as brightness. There is currently no effective and fair standard to measure contrast ratio, so the best way to identify it is to rely on the user's eyes.

Hue

Refers to the relative lightness and darkness of an image, which is expressed as color in color images. Hue is the expression of the reflection and radiation energy intensity of ground objects on the image. The attributes, geometric shapes, distribution ranges and combination rules of ground objects can all be reflected in remote sensing images through hue differences.

Saturation

refers to the vividness of a color, also known as the purity of the color. Saturation depends on the ratio of chromatic and achromatic components (grey) in the color. The greater the color component, the greater the saturation; the greater the achromatic component, the smaller the saturation. Pure colors are highly saturated, such as bright red and bright green. Colors mixed with white, gray or other tones are unsaturated colors, such as purple, pink, yellowish brown, etc.

Baidu Encyclopedia - Contrast

Baidu Encyclopedia - Hue

Baidu Encyclopedia - Saturation