Analysis of the most popular reasons affecting the

  • Detail

Analysis of the reasons affecting the quality of digital image II

II. Pixel depth

image depth refers to the number of bits used to store each pixel (i.e. bits), which is also used to measure the resolution of the image. The pixel depth determines the number of colors that each pixel of a color image may have, or determines the number of gray levels that each pixel of a gray-scale image may have. The more bits used to represent pixels, the more colors a pixel can express, and the deeper its depth. Although color images can be very deep, the deeper the pixels, the larger the storage space required. The pixel depth is too shallow, which affects the quality of the image. The image looks rough and unnatural

bits is the basic element of digital data. Each bit is either on or off, usually represented by 1 or 0, that is, there are only two changes. Each pixel of the scanned image has a pixel depth, such as 1 to 32 bits. The 1-bit image is a black-and-white image (such as the black-and-white line drawing mentioned above). A 2-bit pixel has four variations (0011011), and its color range is from white - light gray - dark gray - black

an 8-bit pixel can express all grays in 256 gray levels, and these colors can be printed by postscript (R) level 2 and level 3 printers. Each pixel of an image is represented by three components: R, G and B. if the depth of each pixel is 8-bit, then each pixel shares 24 bit representation, and each pixel can be one of the colors

when a pixel is represented by a value of 32 bits, if R, G, and B are represented by 8 bits respectively, the remaining 8 bits are often referred to as α Alpha channel bit. There is one in Adobe Photoshop software α Access. More commonly, in a CMYK mode, there are four 8-bit channels, namely cyan channel, magenta channel, yellow channel, and black channel, indicating that the pinion and pinion are in normal operation

III. color model of image

different color representation methods of various color models have an impact on color digital images. The following are the main common color description models

rgb color model

red, green and blue are the three primary colors of color and light, and the three wavelengths of red, green and blue are the basis of all colors in nature. Most of the visible spectrum can be expressed by the mixing of red, green and blue (RGB) light in different proportions and intensities, and cyan, magenta and yellow are generated at the position of color overlap. Because RGB color light synthesis produces white, RGB color model is additive mode. RGB color model is often used in lighting, video and display. For example, the system of color generated on the display is the same as the basic characteristics of light generated in nature: color can be generated by red, green and blue, which is the basis of RGB color model indicators. Most scanners can also use RGB color models to record data of digital images. The color display can emit three kinds of light beams with different intensities, so that the phosphorescent materials with three colors of red, green and blue are covered inside the screen to emit light, so as to generate color. The electro-hydraulic loading, sensor force measurement, digital display force value, printer print force value data, and automatically convert the compressive strength. For example, when you see red in Photoshop, the display turns on its red beam, which stimulates red phosphorus to display a red pixel on the screen

in Photoshop, when using RGB color picker, you can combine red, green and blue color values to change the color of pixels. The color values of the three primary colors range from 0 to 255. R: 255, g:255, b:255 stack produces white, but r:0, g:0, b:o stack produces black (no color light). R: 185, g:132, b:234 superimpose to produce the color as shown in the figure

in connection with the previously mentioned knowledge about image pixel depth, for a crystal clear digital image to be copied on a display connected to a computer equipped with 24 bit color, one color is enough, although it is only a part of the visible colors in nature

cmyk color model

green, magenta and yellow are secondary colors, which are complementary colors of red, green and blue. CMYK color model is based on the light absorption characteristics of ink printed on paper. When white light shines on translucent ink, part of the spectrum is absorbed and part is reflected back to the eyes. Theoretically, pure cyan (c), magenta (m) and yellow (y) pigments can synthesize and absorb all colors and produce black. For this reason, CMYK model is called subtractive model. But in fact, printing inks contain some impurities. These three inks actually produce a kind of earthy gray, which must be mixed with black (k) ink to produce true black (k or BK instead of B is used to avoid confusion with blue). The color of a print is composed of 39% green, 47% magenta, 0% yellow and 1% black (black can absorb all light). This print will reflect 60% red light, 52% green light, and 99% blue light

lab color model

lab color model is based on the international standard for color measurement formulated by the International Commission on illumination (CIE) in 1931. In 1976, this model was revised and named CIELAB, and the lab color design has nothing to do with the equipment; No matter what device (such as monitor, printer, computer or scanner) is used to create or output images, the colors produced by this color mode are consistent. Lab color is composed of psychological lightness component (L) and two chrominance components; These two components are a component (from green to red) and B component (from blue to yellow). The lab image contains 24 (8 × 3) Bit/pixel three channel image

you can use lab mode to process Photo CD images, height and color values in individual images, transfer images between different systems, and print to postscript (R) level 2 and level 3 printers. To print lab images to other color postscript devices, you should first convert them to CMYK. Generally, lab color is the internal color mode used by Photoshop when converting between different color modes

hsb color mode

hsb is based on people's perception of color, not the computer value of RGB, nor the CMYK percentage of the printer. The human eye believes that color is composed of chromaticity, saturation and brightness. HSB model describes three basic characteristics of color:

1 Chroma h, the standard color wheel data backup function from 0 to 360 degrees can also save and view the previously stored data separately, and the hue is measured by position. In common use, hue is identified by color names, such as red, orange, or green. Chromaticity is based on the wavelength of light reflected by the object or transmitted through the object

2. Saturation S refers to the intensity or purity of color. Saturation represents the proportion of color components in the color phase, measured as a percentage from 0% (gray) to 100% (fully saturated). On the standard color wheel, the saturation increases from the center to the edge. Saturation is often called work color. The higher the saturation, the lower the gray component and the higher the intensity of color

3. Height B is the relative lightness of the color, usually measured as a percentage from 0% (black) to 100% (white)

the above four color models are often used in image processing. The color models of images are different, and the color of the table image is of course different. (to be continued)

Copyright © 2011 JIN SHI