Video and image RGB/YUV format details

The color display principle of Computer Color Display is the same as that of color TV sets. The principle of adding and Mixing colors of R (red), g (green), and B (blue) is used: three electron beam with different intensity are emitted to make the red, green, and blue phosphor materials on the inside of the screen emit light and produce color. This color representation method is called RGB Color Space Representation (it is also the most commonly used Color Space Representation Method in multimedia computer technology ).
Based on the three-color principle, any color-light F can be mixed with R, G, and B of different components.
F = R [R] + G [g] + B [B]
R, G, and B are the coefficients of the three colors involved in the mixing. When the three base colors are 0 (weakest), the light is mixed with black light. When the three base colors are K (strongest), the light is mixed with white light. By adjusting the values of the R, G, and B coefficients, you can mix various colors between the black light and the white light.
So where does YUV come from? In Modern Color TV systems, three-channel color cameras or color CCD cameras are usually used for video recording. Then, the color image signals are divided by color, amplified, and corrected to obtain RGB, after the matrix conversion circuit, the Brightness Signal y and two color difference signal R-Y (U) and B-Y (v) are obtained. Finally, the sending end encodes the brightness and color difference Signals respectively, send data over the same channel. The representation of this color is the so-called YUV color space representation.
The importance of using YUV color space is that its brightness signal y is separated from the color signal u and v. If only the Y Signal component is used, but not the U or V component, the black and white gray images are displayed. The color TV uses the YUV space to solve the compatibility problem between the color TV and the black and white TV with the Brightness Signal y, so that the black and white TV can also receive the color TV signal.
The conversion formula between YUV and RGB is as follows (the RGB value ranges from 0 to 255 ):
Y = 0.299r + 0.587G + 0.114b
U =-0.147r-0.289G + 0.436b
V = 0.615r-0.515g-0.100b
R = Y + 1.14 V
G = Y-0.39u- 0.58 V
B = Y + 2.03u
In DirectShow, common RGB formats include rgb1, rgb4, rgb8, rgb565, rgb555, rgb24, rgb32, and argb32; common YUV formats include yuy2, yuyv, yvyu, uyvy, ayuv, y41p, y411, y211, if09, iyuv, yv12, yvu9, yuv411, and yuv420. As the auxiliary description type of the video media type (subtype), their corresponding guids are shown in table 2.3.
Table 2.3 common RGB and YUV formats
Guid format description
Mediasubtype_rgb1 2 color, each pixel is represented by 1 bit, requires a color palette
Mediasubtype_rgb4 16 color, each pixel is represented by four bits, the color palette is required
Mediasubtype_rgb8 256 colors, each pixel is represented by 8 bits, and a color palette is required.
Mediasubtype_rgb565 each pixel is represented by 16 bits. The RGB component uses 5 bits, 6 bits, and 5 BITs respectively.
Mediasubtype_rgb555 each pixel is represented by 16 bits, and the RGB component uses 5 bits (the remaining 1 bits are not needed)
Mediasubtype_rgb24 each pixel is represented by 24 bits, and each RGB component uses 8 bits
Mediasubtype_rgb32 each pixel is represented by 32 bits, and each RGB component uses 8 bits (the remaining 8 bits are not needed)
Mediasubtype_argb32 each pixel is represented by 32 bits, and each RGB component uses 8 bits (the remaining 8 bits are used to represent the alpha channel value)
Mediasubtype_yuy2, in the format
Mediasubtype_yuyv yuyv format (the actual format is the same as that of yuy2)
Mediasubtype_yvyu yvyu format, packaged
Mediasubtype_uyvy uyvy format, packaged
Mediasubtype_ayuv 4: 4 YUV with alpha channel format
Mediasubtype_y41p y41p format, packaged
Mediasubtype_y411 y411 format (the actual format is the same as that of y41p)
Mediasubtype_y211 y211 format
Mediasubtype_if09 if09 format
Mediasubtype_iyuv iyuv format
Mediasubtype_yv12 yv12 format
Mediasubtype_yvu9 yvu9 format
The following describes various RGB formats.
Rgb1, rgb4, and rgb8 are color palette RGB formats. when describing the format details of these media types, the bitmapinfoheader data structure is followed by a color palette (defining a series of colors ). Their image data is not a true color value, but an index of the current pixel color value in the palette. Take rgb1 (2-color Bitmap) as an example. For example, if the two color values defined in the palette are 0x000000 (black) and 0 xffffff (white), then the image data is 001101010111... (Each pixel is represented by one digit.) The color of each pixel is black, black, white, black, white, black, black, and white ....
22 rgb565 uses 16 bits to represent a pixel. 5 bits in the 16 bits are used for R, 6 bits are used for G, and 5 bits are used for B. Program A word (word, a word is equal to two bytes) is usually used to operate a pixel. After a pixel is read, the meaning of each bit of the word is as follows:
High byte and low byte
R g B
The value of each RGB component can be obtained by combining the shielded word and the shift operation:
# Define rgb565_mask_red 0xf800
# Define rgb565_mask_green 0x07e0
# Define rgb565_mask_blue 0x001f
R = (wpixel & rgb565_mask_red)> 11; // value range: 0-31
G = (wpixel & rgb565_mask_green)> 5; // value range: 0-63
B = wpixel & rgb565_mask_blue; // value range: 0-31
Rgb555 is another 16-bit RGB format. The RGB component is represented by 5 bits (the remaining 1 bits are not used ). After reading a pixel with a word, the meaning of each bit of the word is as follows:
High byte and low byte
X r r g B (X indicates no, can be ignored)
The value of each RGB component can be obtained by combining the shielded word and the shift operation:
# Define rgb555_mask_red 0x7c00
# Define rgb555_mask_green 0x03e0
# Define rgb555_mask_blue 0x001f
R = (wpixel & rgb555_mask_red)> 10; // value range: 0-31
G = (wpixel & rgb555_mask_green)> 5; // value range: 0-31
B = wpixel & rgb555_mask_blue; // value range: 0-31
Rgb24 uses 24 bits to represent a pixel, and RGB is represented by 8 bits. The value range is 0-255. Note that the order of RGB components in the memory is BGR .... Generally, you can use the rgbtriple data structure to operate a pixel, which is defined:
Typedef struct tagrgbtriple {
Byte rgbtblue; // blue weight
Byte rgbtgreen; // green component
Byte rgbtred; // red weight
} Rgbtriple;
Rgb32 uses 32 bits to represent a pixel. Each RGB component uses 8 bits. The remaining 8 bits are used as the alpha channel or are not used. (Argb32 is rgb32 with alpha channel .) Note that the order of RGB components in the memory is bgra .... Generally, you can use the rgbquad data structure to operate a pixel, which is defined:
Typedef struct tagrgbquad {
Byte rgbblue; // blue weight
Byte rgbgreen; // green component
Byte rgbred; // red weight
Byte rgbreserved; // reserved bytes (used as alpha channel or ignored)
} Rgbquad;
The following describes various YUV formats. The YUV format generally has two categories: packed format and planar format. The former stores the YUV component in the same array, usually several adjacent pixels constitute a macro pixel (macro-pixel), while the latter uses three arrays to separate the three components of YUV, it is like a three-dimensional plane. In table 2.3, yuy2 to y211 are both in the packaging format, while if09 to yvu9 are in the flat format. (Note: When introducing various formats, each YUV component carries a subscript. For example, y0, U0, and V0 indicate the yuv component of the first pixel, y1, u1, and V1 indicate the YUV component of the second pixel, and so on .)
The yuy2 (and yuyv) format retains the Y component for each pixel, while the UV component samples every two pixels horizontally. A macro pixel is 4 bytes, which actually represents 2 pixels. (Means that a macro pixel contains four Y components, two U components, and two v components .) The YUV component order in the image data is as follows:
Y0 U0 Y1 V0 Y2 U2 Y3 V2...
The yvyu format is similar to yuy2, except that the order of YUV components in the image data is different:
Y0 V0 Y1 U0 Y2 V2 Y3 U2...
The format of uyvy is similar to that of yuy2, but the order of YUV components in image data is different:
U0 y0 V0 Y1 U2 Y2 V2 Y3...
The ayuv format has an alpha channel and extracts YUV components for each pixel. The image data format is as follows:
A0 y0 U0 V0 A1 Y1 U1 V1...
The y41p (and y411) format retains the Y component for each pixel, while the UV component samples every 4 pixels horizontally. A macro pixel is 12 bytes, which actually represents 8 pixels. The YUV component order in the image data is as follows:
U0 y0 V0 Y1 U4 Y2 V4 Y3 Y4 Y5 y6 Y8...
In the y211 format, the Y component is sampled every two pixels in the horizontal direction, while the UV component is sampled every four pixels. A macro pixel is 4 bytes, which actually represents 4 pixels. The YUV component order in the image data is as follows:
Y0 U0 Y2 V0 Y4 U4 y6 V4...
The yvu9 format extracts the Y component for each pixel. When the UV component is extracted, the image is first divided into several 4x4 macro blocks, then, each Macro Block extracts one u component and one V component. When storing image data, the first is the array of Y components of the entire image, followed by the U Component Array and the V Component Array. The if09 format is similar to yvu9.
The iyuv format extracts the Y component for each pixel. When the UV component is extracted, the image is first divided into several 2x2 macro blocks, then, each Macro Block extracts one u component and one V component. The yv12 format is similar to that of iyuv.
The yuv411 and yuv420 formats are mostly used in DV data. The former is used in NTSC and the latter is used in palth. Yuv411 extracts the Y component for each pixel, while the UV component samples every four pixels horizontally. Yuv420 does not mean that the V component sampling is 0. Compared with yuv411, it increases the color difference sampling frequency by one time in the horizontal direction, and reduces the color difference sampling by half at the U/V interval in the vertical direction, as shown in.