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Imaging parameters introduction(Part 2)

Color is an important indicator of endoscopic systems. Do you know what factors affect the color of endoscopic system and how to adjust system parameters to obtain the image color you want? Let’s learn more

1. Color Mode

In image processing, common color models include HSB, RGB, CMYK, CIEXYZ, CIELUV, CIELAB, etc. In the HSB color model, hue, saturation, and brightness are the basic descriptions of image properties.

Hue is the color reflected from or transmitted through an object. Hue is measured by position on the standard color wheel from 0° to 360°. Typically, hue is identified by a color name, such as red, orange, or green.

Saturation refers to the intensity or purity of a color. Saturation represents the proportion of the gray component of the hue, measured as a percentage from 0% (gray) to 100% (a fully saturated pure color).

Lightness is the relative lightness or darkness of a color, usually measured as a percentage from 0% (black) to 100% (white).

2.Color Gamut

Color gamut

  • Color gamut refers to the range area formed by the number of colors that a certain device can express, that is, the range of colors that various screen display devices, printers or printing devices can express. The colors of the visible spectrum in nature constitute the largest color gamut space of all colors that the human eye can see.
  • The size of the device color gamut space is related to the device, medium, and observation conditions. A device with a larger color gamut displays more colors.
  • The CIE-xy chromaticity diagram developed by the CIE International Association of Illumination is used to visually express the color gamut. In the CIE-xy chromaticity diagram, the range of color gamuts that various display devices can express can be represented by a triangle area composed of RGB three-point lines. The larger the area of the triangle, it means the range of color gamut of the display device. bigger.


BT Standard

  • BT.2020: In 2013, the BT.2020 standard for a new generation of UHD (Ultra-high definition) video production and display system promulgated by the International Telecommunication Union Radiocommunication Sector (ITU-R), redefined TV broadcasting and consumption Various parameters and indicators of ultra-high-definition video display in the electronic field promote the further standardization of 4K UHD home display equipment, which can display high-density dark green, orange, etc. BT2020 is more suitable for outdoor scenes
  • BT709: It is a standard for high-definition (1080P) video production and display systems released by ITU-R. BT709 is more in line with the color requirements of doctors for scenes in human body chambers.


3.Color Temperature and White Balance

Color Temperature

Color temperature is a physical quantity used in lighting optics to define the color of a light source. That is, when a black body is heated to a temperature, and the color of the light emitted by it is the same as that emitted by a light source, the temperature at which the black body is heated is called the color temperature of the light source, or color temperature for short. Its unit is represented by “K” (Kelvin temperature unit).


The color rendering index of the light source(CRI)

The effect of a light source on the color appearance of an object compared to a standard reference light source. The closer the CRI is to 100, the better the color rendering of the light source. The lower the CRI, the darker the object color.

White balance is closely related to color temperature

Images under different color temperature light sources will show different degrees of color cast. “Low color temperature, warm colors; high color temperature, cool colors”.

The human eye has color constancy and can adapt to different color temperature environments. Therefore, unless the color temperature of the light source is very extreme, the human eye will automatically adjust the same white object to white when viewed under different light (color temperature).

White balance is to simulate the ability of the human eye to automatically adjust the color and restore the actual color of the object. That is, “Regardless of any light source, white objects can be restored to white.”


4. Other Color Factors


The broad definition of the gamma value is the power exponential relationship between the input value and the output value, which is used to compensate for the nonlinear perception of natural brightness by the human eye. Gamma adjustment can convert the linear information obtained by the photosensitive element into non-linear information similar to the human eye after adjustment. Adjusting the gamma can change the details of the output picture to a certain extent.


Image contrast refers to the measurement of the different brightness levels between the brightest white and the darkest black in the light and dark areas of an image, that is, the size of the grayscale contrast of an image.

Generally speaking, the higher the contrast, the clearer and more eye-catching the image, and the brighter the color; while the lower the contrast, the whole picture will be gray.


Gain adjustment is to adjust the upper limit value that limits the amplification of image signals. The gain control is the upper limit of the signal gain. The higher the gain, the more sensitive the light sensor, the higher the brightness of the image, and the noise will be amplified. Generally, it is recommended to increase it in scenes with insufficient illumination, and it is recommended to lower it in scenes with strong point light sources to suppress overexposure of point light sources.

5.Color Reproduction of Endoscopy System

The degree of color reproduction is to adjust the white balance, contrast and chroma to make the color of the image generally consistent with the color of the original scene, and the effect is restored to the most suitable feeling for human eyes.

For example, chroma adjustment: adjust the brightness of the color to make the image color fuller and closer to reality


Contrast adjustment: Make the image more layered and enhance the visual effect.

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