rgb与cmyk颜色de区别(The difference between RGB and CMYK color de)
rgb与cmyk颜色de区别(The difference between RGB and CMYK
color de)
RGB colors and CMYK colors are two different color patterns.
The RGB color pattern is the most basic color pattern, so the RGB color pattern is an important pattern. As long as the image displayed on the computer screen, it must be in RGB mode. Because the physical structure of the display is to follow the RGB.
CMYK, also called print color patterns, is printed as the name suggests.
It's a big difference compared to RGB:
The RGB mode is a luminous color pattern, and you can still see the contents on a screen in a dark room;
CMYK is a reflective color pattern. How do we read the content of the newspaper? Sunlight or light shines on the newspaper, and then reflects into our eyes to see the content.
It requires an external light source, and you cannot read the newspaper if you are in the dark room.
As long as the image displayed on the screen is RGB mode performance. The image that is seen on the printed material is the CMYK pattern.
For example, periodicals, magazines, newspapers, posters and
so on are printed out, and that is the CMYK model.
Similar to RGB, CMY is the first letter of the 3 printing inks: cyan, Cyan, magenta, Magenta, yellow, Yellow.
The K takes the last letter of the black, so it does not take the initial letter to avoid confusion with Blue.
In theory, it's enough to just need CMY three inks, and the three of them should be black together.
But because the current manufacturing process can not produce high purity ink, the result of CMY addition is actually a dark red. It also needs to add a special black ink and.
In Photoshop, to understand the pattern concept is very important, because the color mode display and print electronic image color model (simple color model is a mathematical algorithm for color), a pair of electronic images in what ways in the computer display or printout. The common color mode including bitmap mode, gray model, double tone mode, HSB (hue, saturation, brightness (RGB) mode, said that the red, green and blue) model, CMYK (cyan, magenta, yellow, said black) model, Lab model, index color mode, multi channel mode and 8 bit /16 a number of image model, each model is described and the principle and can reproduce the color display color is different.
In addition to determining the number of colors that can be displayed in the image, the color pattern also affects the number of channels and the size of the file. The channel
mentioned here is also an important concept in Photoshop, where each Photoshop image has one or more channels, each storing information about the color elements in the image. The default number of color channels in an image depends on its color pattern. For example, CMYK image has at least four channel resolution on behalf of green, yellow and black, magenta information. In addition to these default color channels, additional channels can also be called the Alpha channel is added to the image, so as to store and edit the selection mask, and can add the color channel. An image sometimes has as many as 24 channels, by default,
Bitmap mode, gray tone, and index color are still a channel in the image; RGB and Lab images have three channels; the CMYK image has four channels.
One, HSB mode
The HSB model is based on the human eye's observation of colors, in which all colors are represented by three characteristics, hue or hue, saturation, or brightness.
1. hue (H)
Hue is the color, physical, and psychological characteristics associated with the main wavelength of the color. From the experiment it is known that the visible light of different wavelengths has different colors. Many wavelengths of light can be mixed in different proportions to form a wide variety of colors, but as long as the wavelength composition is certain, then the color is determined. Non color (black, 100, gray) does
not exist hue attributes; all colors (red, orange, yellow, green, green, blue, purple, etc.) are the attributes that indicate the appearance of color. They are all hues, and sometimes hue is also called hue.
2. saturation (S)
Saturation refers to the intensity or purity of a color, representing the proportion of gray components in the hue, expressed in 0%-100% (solid color).
3. brightness (B)
Brightness is the relative degree of brightness of a color, usually measured by 0% (black) -100% (white).
Two, RGB mode
RGB model is the mixing principle of 3 primary colors of light in nature based on the red (Red), green (Green) and blue (Blue) color according to 3 from 0 (black) to 255 (white) the brightness value distribution in each color, so as to specify the color. When the primary colors of different brightness are mixed, they produce 256*256*256 colors, about 16 million 700 thousand. For example, a bright red may have a R value of 246, a G value of 20, and a B value of 50. When the brightness values of the 3 primary colors are equal, they produce gray; when 3 brightness values are 255, pure white is produced; and when all brightness values are 0, pure black is produced. When the color of the 3 colors is mixed, the color is generally higher than the original color, so the method of generating color in the
RGB mode is also called "color plus color".
Three, CMYK mode
The CMYK color mode is a print mode. Four of these letters refer to cyan (Cyan), magenta (Magenta), yellow (Yellow) and black (Black), which represent four colors of ink in printing. CMYK mode is not what the essential difference with the RGB model, the principle of only the different colors, color mixing color emitted from the light source in the RGB mode, and in the CMYK mode by the light to have different proportions of C, M, Y, K ink on paper, part of the spectrum is absorbed by reflection light color eye. Because of C, M, Y, K in the mixed color, with the increase of C, M, Y, K four components of the reflected light to the human eye will be less and less, the brightness of the light will be more and more low, all CMYK color mode is also called subtractive color.
Four, Lab mode
The prototype of the Lab model was defined by the CIE society in 1931 as a measure of color. It was redefined and named CIELab in 1976. This pattern solves the difference in color support caused by different displays and print devices, that is, it does not rely on the device.
The Lab color is represented by a luminance component L and two color components a and B. The range of L is 0-100, and the a component represents the spectral change from green to red, while the B component represents the spectral change from blue to yellow, and the ranges of a and B are -120-120.
The Lab pattern contains the widest range of colors that can contain all the colors in the RGB and CMYK modes. The CMYK model contains the fewest colors, some on the screen, but not the printed colors on the printed matter.
Five, other color patterns
In addition to the basic RGB model, CMYK model and Lab model, Photoshop support (or processing) other color models, these models include bitmap mode, gray model, double tone mode, indexed color mode and multi channel mode. And these color patterns have special uses. For example, grayscale images only have gray values without color information; index color patterns, although they can use colors, can be used in a relatively small amount of color relative to RGB mode and CMYK mode. Here are some of these color patterns.
1. bitmap (Bitmap) mode
Bitmap patterns represent pixels in an image in two colors (black and white). Bitmap images are also called black and white images. Because of its depth of 1, also known as an image. Since bitmap patterns represent only the pixels of the image in black and white, a large amount of detail is lost when converting the image to bitmap mode, so Photoshop provides several algorithms to simulate lost details in the image.
In the same width, height, and resolution, bitmap images have the smallest size, approximately 1/7 of grayscale mode and below 1/22 of RGB mode.
2. gray scale (Grayscale) mode
Grayscale mode can use up to 256 gray level to show the image, so that the transition of the image is more smooth and delicate. Each pixel of the grayscale image has a brightness value between 0 (black) to 255 (white). Gray values can also be represented by the percentage of black ink covered (0% equals white and 100% is black). Images produced by black fold or grayscale scanners are often shown in grayscale.
3. tone (Duotone) mode
Two tone mode using 2-4 color ink to create a two tone (2 colors), three color (3 colors) and four color (4 colors) the mixed levels of an image. In converting a grayscale image into a two tone mode, the tone can be edited to produce a special effect. The use of dual tone mode is the main use of less color as many shades, it is very important to reduce the cost of printing, because when printing, each additional colors are in need of greater cost.
4. index color (Indexed Color) mode
Index color patterns are commonly used in online and animated images. When the color image is converted to an indexed color, the image contains nearly 256 colors. The index color image contains a color table. If the color in the original image cannot be represented by 256 colors, Photoshop will select the closest colors from the available colors to simulate the colors so that the size of the image file can be reduced.
Used to store the colors in an image and to establish a color index for those colors. The color table can be defined during conversion or modified after the claimed index image.
5. multi channel (Multichannel) mode
Multi channel mode is very useful for images with special printing requirements. For example, if only one or two or two or three colors are used in the image, multi channel mode can reduce the printing cost and guarantee the correct output of the image color.
6.8 bit /16 bit channel mode
In grayscale RGB or CMYK mode, 16 bit channels can be used instead of the default 8 bit channel. According to the default, 8 channel contains 256 levels, if increased to 16, the number of levels of each channel is 65536, it can get more color detail. Photoshop can recognize and input images of 16 bit channels, but there are so many restrictions on this image that none of the filters can be used, and the other 16 bit channels cannot be printed.
Six, color mode conversion
In order to output images correctly on different occasions, it is sometimes necessary to convert an image from one mode to another. Photoshop converts the desired color pattern by executing the commands in the Image/Mode (image / mode) submenu. The conversion of this color pattern sometimes changes the
color values in the image permanently. For example, when converting RGB mode images to CMYK mode images, the RGB color values beyond the CMYK gamut are adjusted outside the CMYK gamut, thus narrowing the color range.
Since some colors lose part of the color information after conversion, it is better to save a backup file before converting so that the image can be restored when necessary.
1. converts the color image to grayscale mode
When converting a color image to a grayscale pattern, Photoshop will throw out all the color information in the original image, leaving only the gray level of the pixel.
Grayscale mode can be used as the intermediary mode between bitmap mode and color mode.
2. converts other modes of images to bitmap mode
Converting the image to bitmap mode reduces the image color to two, thus greatly simplifying the color information in the image and reducing the file size. To convert an image to bitmap mode, you must first convert it to grayscale mode. This removes the hue and saturation information of pixels, leaving only the brightness values. However, since very few edit options can be used in bitmap mode images, it is better to edit images in grayscale mode and then convert them.
In grayscale mode, the edited bitmap mode image may look different when converted back to bitmap mode. For example, in
bitmap mode, black pixels, which are edited in grayscale mode, may be gray. If the pixel is bright enough, when converted back to bitmap mode, it will become white.
3. converts other patterns into index patterns
When converting a color image to an index color, many of the colors in the image are removed, while only 256 of them are preserved, the standard colors supported by many multimedia animation applications and web pages. Only grayscale and RGB patterns can be converted to indexed color patterns. Since the grayscale model itself is composed of 256 levels of gray,
Therefore, there is no significant difference between the color and the image size after indexing to the color. However, when the RGB model is converted to an indexed color pattern, the size of the image will be significantly reduced and the visual quality of the image will be impaired.
4. converts RGB mode images to CMYK mode
If you convert RGB mode images into CMYK mode, the colors in the image will be separated, and the gamut of colors will be limited. Therefore, if the image is in RGB mode, it is better to edit it in RGB mode and then convert it into a CMYK image.
5. using Lab mode for mode conversion
In the color pattern that Photoshop can use, the Lab pattern has the widest gamut, including all the colors in the RGB and CMYK gamut. Therefore, converting to Lab mode does not cause
any loss of color. Photoshop uses the Lab mode as an internal conversion mode to accomplish conversions between different color patterns. For example, when converting RGB mode images to CMYK mode, the computer first converts the RGB mode to Lab mode, and then converts the Lab mode image to the CMYK mode image.
6. converts other patterns into multimodal modes
A multimodal mode can be obtained by converting color patterns and removing the color channels of the original image.
CMYK images will be converted to multi channel mode can be created by cyan, magenta, yellow and black color (the color is special premixed ink, used to replace or supplement the four-color ink printing; spot color channel is a special color channel. To add a preview for spot color image) Constructed image.
Image RGB images will be converted to multi channel mode to create a green, magenta and yellow color.
Removing a channel from an RGB, CMYK, or Lab image automatically converts the image to a multimodal mode. The original channel is converted to spot color channel.
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