Data compression (four)-color space conversion (non-sampling version) (2024)

experiment one:

  • Write RGB to YUV program, focus on function definition, initialization and calling of some lookup tables, buffer allocation. Convert the obtained RGB file to YUV file and watch it with YUV Viewer player to verify whether it is correct.

  • Write a program to convert YUV to RGB. Use this program to convert the given experimental data into RGB files. And with the original

    RGB files are compared, and if there are errors, analyze where the errors come from.

Article Directory

  • (1) Conversion formula and file storage format of YUV and RGB
  • (Two) the command line parameters of the main function
    • 2.1 Representation
    • 2.2 How to use
  • (3) Preliminary realization of color space conversion (no sampling) code
    • main.cpp
    • rgb2yuv.h
    • rgb2yuv.cpp
    • yuv2rgb.h
    • yuv2rgb.cpp
    • Experimental results
  • (4) Analysis of the causes of experimental errors and code modification
    • Error correction
    • Experimental results
  • (5) Optimize the code (using the lookup table method)
    • main.cpp
    • yuvrgb.h
    • yuvrgb.cpp
    • Experimental results

R=(298×Y+411×V57344)>>8G=(298×Y101×U211×V+34739)>>8B=(298×Y+519×U71117)>>8Y=(66×R+129×G+25×B)>>8+16U=(38×R74×G+112×B)>>8+128V=(112×R94×G18×B)>>8+128\begin{aligned} &R=(298\times Y+411\times V-57344)>>8\\ &G=(298\times Y-101\times U-211\times V+34739)>>8\\ &B=(298\times Y+519\times U-71117)>>8\\ &Y=(66\times R+129\times G+25\times B)>>8+16\\ &U=(-38\times R-74\times G+112\times B)>>8+128\\ &V=(112\times R-94\times G-18\times B)>>8+128 \end{aligned}R=(298×Y+411×V57344)>>8G=(298×Y101×U211×V+34739)>>8B=(298×Y+519×U71117)>>8Y=(66×R+129×G+25×B)>>8+16U=(38×R74×G+112×B)>>8+128V=(112×R94×G18×B)>>8+128

  The above formula is already quantified.

  Check out the information,RGBRGBRGBThe file storage format isBGRBGRBGRBGR BGR BGR\cdotsBGRBGRBGR,YUVYUVYUVThe file storage format is first save allYYY, Save allUUUAnd finally save allVVV

2.1 Representation

  One programmain()main()main()The function can contain two parameters:

  • The first parameter isintintintTypes of;
  • The second parameter is a string array;

  Usually, the first parameter is namedargcargcargc, The second parameter isargvargvargv. Since the declaration of the string array in the function header can have two forms, somain()main()main()There are also two ways to write functions.

  1. main()main()main()functionWriting one

    int main(int argc, char** argv){ return 0;}
  2. main()main()main()functionWriting two:

    int main(int argc, char* argv[]){ return 0;}

2.2 How to use

  • The meaning of the parameters:

      int argc​: Represents the number of strings.argc = 1 + the number of strings entered by the user, The value of argc is calculated automatically by the operating system, and the programmer does not need to assign it.

      char argv[]*: It stores multiple strings, the form of the string is as follows:

    argv[0] = the name of the executable file. For example, change.exe. (This string does not require user input, and is the same as argc, which can be automatically generated by the operating system.

    argv[1] = string 1

    argv[2] = string 2

    argv[3] = string 3

    \vdots

  • How to input parameters in programming mode?

  The platform used isVisualStudio2019Visual Studio 2019VisualStudio2019, The file to be used isdown.rgbdown.rgbdown.rgb, The file to be generated isup.yuv,cho.rgbup.yuv,cho.rgbup.yuv,cho.rgb,The steps of parameter input are shown in the following figure:

1. Open the properties window of the upper taskbar debugging interfaceData compression (four)-color space conversion (non-sampling version) (1)
2. Select debug in configuration propertiesData compression (four)-color space conversion (non-sampling version) (2)
3. Modify the command parameters as requiredData compression (four)-color space conversion (non-sampling version) (3)

  Based on the above knowledge, the preliminary realization of color space conversion can be easily carried out. Header filergb2yuv.h,yuv2rgb.hrgb2yuv.h,yuv2rgb.hrgb2yuv.h,yuv2rgb.hAnd source filesmain.cpp,rgb2yuv.cpp,yuv2rgb.cppmain.cpp,rgb2yuv.cpp,yuv2rgb.cppmain.cpp,rgb2yuv.cpp,yuv2rgb.cppcomposition.

  Solution Explorer is shown in the figure below:

Data compression (four)-color space conversion (non-sampling version) (4)

  Experiment codeas follows:

main.cpp

#include <iostream>#include <cstdio>#include <fstream>#include "rgb2yuv.h"#include "yuv2rgb.h"using namespace std;#define size 196608#define usize 65536#define vsize 131072using namespace std;int main(int argc, char** argv){ifstream infile(argv[1],ios::binary);ofstream outYUV(argv[2], ios::binary);ofstream outRGB(argv[3], ios::binary);if (!infile) { cout << "error to open file1!" << endl; }if (!outYUV) { cout << "error to open file2" << endl; }if (!outRGB) { cout << "error to open file3" << endl; }unsigned char* in = new unsigned char[size];unsigned char* YUV = new unsigned char[size];unsigned char* RGB = new unsigned char[size];infile.read((char*)in, size);rgb2yuv(in,YUV,size, usize, vsize);//First conversionyuv2rgb(YUV, RGB, usize, vsize);//The second conversion/*for (int i = 0; i < size; i++){if (abs(in[i] - RGB[i]) > 5)cout << "i=" << i << " in[" << i << "]=" << int(in[i]) << " RGB[" << i << "]=" << int(RGB[i]) << endl;}*/outYUV.write((char*)YUV, size);outRGB.write((char*)RGB, size);delete in;delete YUV;delete RGB;infile.close();outYUV.close();outRGB.close();return 0;}

rgb2yuv.h

#pragma oncevoid rgb2yuv(unsigned char* rgb, unsigned char* yuv, int size,int usize,int vsize);

rgb2yuv.cpp

void rgb2yuv(unsigned char* rgb, unsigned char* yuv,int size,int usize,int vsize){unsigned char r, g, b, y, u, v;int j = 0;for (int i = 0;i < size;){b = *(rgb + i);g = *(rgb + i + 1);r = *(rgb + i + 2);y = ((66 * r + 129 * g + 25 * b) >> 8) + 16;u = ((-38 * r - 74 * g + 112 * b) >> 8) + 128;v = ((112 * r - 94 * g - 18 * b) >> 8) + 128;*(yuv + j) = y;*(yuv + j + usize) = u;*(yuv + j + vsize) = v;i = i + 3;//Each rgb is 1 groupj++;}}

yuv2rgb.h

#pragma oncevoid yuv2rgb(unsigned char* yuv, unsigned char* rgb,int usize,int vsize);

yuv2rgb.cpp

#pragma once#include "yuv2rgb.h"#include <iostream>using namespace std;void yuv2rgb(unsigned char* yuv, unsigned char* rgb,int usize,int vsize){unsigned char r, g, b, y, u, v;int j = 0;for (int i = 0; i < usize; i++){y = *(yuv + i);u = *(yuv + i + usize);v = *(yuv + i + vsize);r = (298 * y + 411 * v - 57344) >> 8;g = (298 * y - 101 * u - 211 * v + 34739) >> 8;b = (298 * y + 519 * u - 71117) >> 8;*(rgb + j) = b;*(rgb + j + 1) = g;*(rgb + j + 2) = r;j = j + 3;}}

Experimental results

down.rgbup.yuvcho.rgb
Data compression (four)-color space conversion (non-sampling version) (5)Data compression (four)-color space conversion (non-sampling version) (6)Data compression (four)-color space conversion (non-sampling version) (7)

among them,down.rgbdown.rgbdown.rgbwithcho.rgbcho.rgbcho.rgbuseYUVviewerPlusYUVviewerPlusYUVviewerPlusThe way to open is:

Data compression (four)-color space conversion (non-sampling version) (8)

  The opened image is an inverted image (due tobmpbmpbmpThe image format is stored backwards, so.rgb.rgb.rgbImage usebmpbmpbmpIt will fall when the mode is opened). The pictures in the above table have been rotated using WeChat for easy identification, butYUVYUVYUVFiles andRGBRGBRGBThere is still mirror flipping between files, but it does not affect viewing and comparison.

  up.yuvup.yuvup.yuvuseYUVviewerPlusYUVviewerPlusYUVviewerPlusThe way to open is:

Data compression (four)-color space conversion (non-sampling version) (9)

  It can be seen from the comparison chart of the three images,RGBtoYUVRGB to YUVRGBtoYUV'S experiment was successfully completed, andYUVtoRGBYUVtoRGBYUVtoRGBThere is a problem with the experiment, which is transferred outcho.rgbcho.rgbcho.rgbThere are more red noise in the image.

Error correction

  Inferred available, in progressYUVtoRGBYUVtoRGBYUVtoRGBWhen you getRGBRGBRGBThree figures may exceedunsignedcharunsigned\ charunsignedcharThe range that the type can represent, that is, possible<0<0<0or>255>255>255

   So it’s necessary toyuv2rgb.cppyuv2rgb.cppyuv2rgb.cppThe file is appropriately revised,>255>255>255Values ​​are direct=255=255=255,<0<0<0Values ​​are direct=0=0=0

  After modificationyuv2rgb.cppyuv2rgb.cppyuv2rgb.cppIs as follows:

#pragma once#include "yuv2rgb.h"#include <iostream>using namespace std;void yuv2rgb(unsigned char* yuv, unsigned char* rgb,int usize,int vsize){int r, g, b, y, u, v;int j = 0;for (int i = 0; i < usize; i++){y = int(*(yuv + i));u = int(*(yuv + i + usize));v = int(*(yuv + i + vsize));r = (298 * y + 411 * v - 57344) >> 8;if (r > 255) { r = 255; }if (r < 0) { r = 0; }g = (298 * y - 101 * u - 211 * v + 34739) >> 8;if (g > 255) { g = 255; }if (g < 0) { g = 0; }b = (298 * y + 519 * u - 71117) >> 8;if (b > 255) { b = 255; }if (b < 0) { b = 0; }*(rgb + j) = unsigned char(b);*(rgb + j + 1) = unsigned char(g);*(rgb + j + 2) = unsigned char(r);j = j + 3;}}

Experimental results

down.rgbup.yuvcho.rgb
Data compression (four)-color space conversion (non-sampling version) (10)Data compression (four)-color space conversion (non-sampling version) (11)Data compression (four)-color space conversion (non-sampling version) (12)

  So far, almost doneRGBtoYUVRGB to YUVRGBtoYUVwithYUVtoRGBYUVtoRGBYUVtoRGBTwo experiments.

  Using a lookup table to optimize the code. Header fileyuvrgb.hyuvrgb.hyuvrgb.hAnd source filesmain.cpp,yuvrgb.cppmain.cpp,yuvrgb.cppmain.cpp,yuvrgb.cppcomposition.

  Solution Explorer is shown in the figure below:

Data compression (four)-color space conversion (non-sampling version) (13)

main.cpp

#include <iostream>#include <cstdio>#include <fstream>#include "yuvrgb.h"using namespace std;#define size 196608#define usize 65536#define vsize 131072#define height 256#define weight 256//Lookup table initializationint* RGBYUV298 = new int[256];int* RGBYUV411 = new int[256];int* RGBYUV101 = new int[256];int* RGBYUV211 = new int[256];int* RGBYUV519 = new int[256];int* RGBYUV66 = new int[256];int* RGBYUV129 = new int[256];int* RGBYUV25 = new int[256];int* RGBYUV38 = new int[256];int* RGBYUV74 = new int[256];int* RGBYUV112 = new int[256];int* RGBYUV94 = new int[256];int* RGBYUV18 = new int[256];int main(int argc, char** argv){initLookupTable();ifstream infile(argv[1],ios::binary);ofstream outYUV(argv[2], ios::binary);ofstream outRGB(argv[3], ios::binary);if (!infile) { cout << "error to open file1!" << endl; }if (!outYUV) { cout << "error to open file2" << endl; }if (!outRGB) { cout << "error to open file3" << endl; }unsigned char* infi = new unsigned char[size];unsigned char* YUVfi = new unsigned char[size];unsigned char* RGBfi = new unsigned char[size];infile.read((char*)infi, size);rgb2yuv(infi, YUVfi, size, usize, vsize);yuv2rgb(YUVfi, RGBfi, usize, vsize);outYUV.write((char*)YUVfi, size);outRGB.write((char*)RGBfi, size);fileend(infi,YUVfi,RGBfi);infile.close();outYUV.close();outRGB.close();return 0;}

yuvrgb.h

#pragma oncevoid yuv2rgb(unsigned char* yuv, unsigned char* rgb,int usize,int vsize);void rgb2yuv(unsigned char* rgb, unsigned char* yuv, int size, int usize, int vsize);void initLookupTable();void fileend(unsigned char* infi, unsigned char* YUVfi, unsigned char* RGBfi);

yuvrgb.cpp

#pragma once#include "yuvrgb.h"#include <iostream>using namespace std;extern int* RGBYUV298;extern int* RGBYUV411;extern int* RGBYUV101;extern int* RGBYUV211;extern int* RGBYUV519;extern int* RGBYUV66 ;extern int* RGBYUV129;extern int* RGBYUV25 ;extern int* RGBYUV38 ;extern int* RGBYUV74 ;extern int* RGBYUV112;extern int* RGBYUV94 ;extern int* RGBYUV18 ;void initLookupTable(){for (int i = 0; i < 256; i++){RGBYUV298[i] = 298 * i;RGBYUV411[i] = 411 * i;RGBYUV101[i] = 101 * i;RGBYUV211[i] = 211 * i;RGBYUV519[i] = 519 * i;RGBYUV66[i] = 66 * i;RGBYUV129[i] = 129 * i;RGBYUV25[i] = 25 * i;RGBYUV38[i] = 38 * i;RGBYUV74[i] = 74 * i;RGBYUV112[i] = 112 * i;RGBYUV94[i] = 94 * i;RGBYUV18[i] = 18 * i;}}void yuv2rgb(unsigned char* yuv, unsigned char* rgb,int usize,int vsize){int r, g, b, y, u, v;int j = 0;for (int i = 0; i < usize; i++){y = int(*(yuv + i));u = int(*(yuv + i + usize));v = int(*(yuv + i + vsize));/*r = (298 * y + 411 * v - 57344) >> 8;*/r = (RGBYUV298[y]+ RGBYUV411[v]-57344)>>8;if (r > 255) { r = 255; }if (r < 0) { r = 0; }/*g = (298 * y - 101 * u - 211 * v + 34739) >> 8;*/g = (RGBYUV298[y] - RGBYUV101[u] - RGBYUV211[v] + 34739) >> 8;if (g > 255) { g = 255; }if (g < 0) { g = 0; }/*b = (298 * y + 519 * u - 71117) >> 8;*/b = (RGBYUV298[y] + RGBYUV519[u] - 71117) >> 8;if (b > 255) { b = 255; }if (b < 0) { b = 0; }*(rgb + j) = unsigned char(b);*(rgb + j + 1) = unsigned char(g);*(rgb + j + 2) = unsigned char(r);j = j + 3;}}void rgb2yuv(unsigned char* rgb, unsigned char* yuv, int size, int usize, int vsize){int r, g, b, y, u, v;int j = 0;for (int i = 0; i < size;){b = int(*(rgb + i));g = int(*(rgb + i + 1));r = int(*(rgb + i + 2));/*y = ((66 * r + 129 * g + 25 * b) >> 8) + 16;*/y = ((RGBYUV66[r] + RGBYUV129[g] + RGBYUV25[b]) >> 8) + 16;/*u = ((-38 * r - 74 * g + 112 * b) >> 8) + 128;*/u = ((-RGBYUV38[r] - RGBYUV74[g] + RGBYUV112[b]) >> 8) + 128;/*v = ((112 * r - 94 * g - 18 * b) >> 8) + 128;*/v = ((RGBYUV112[r] - RGBYUV94[g] - RGBYUV18[b]) >> 8) + 128;/*if ((y > 255) || (u > 255) || (v > 255) || (y < 0) || (u < 0) || (v < 0)){cout << "y=" << y << "u=" << u << "v=" << v << endl;}*/*(yuv + j) = unsigned char(y);*(yuv + j + usize) = unsigned char(u);*(yuv + j + vsize) = unsigned char(v);i = i + 3;//Each rgb is 1 groupj++;}}void fileend(unsigned char* infi, unsigned char* YUVfi, unsigned char* RGBfi){delete infi;delete YUVfi;delete RGBfi;deleteRGBYUV298;deleteRGBYUV411;deleteRGBYUV101;deleteRGBYUV211;deleteRGBYUV519;deleteRGBYUV66;deleteRGBYUV129;deleteRGBYUV25;deleteRGBYUV38;deleteRGBYUV74;deleteRGBYUV112;deleteRGBYUV94;deleteRGBYUV18;}

Experimental results

down.rgbup.yuvcho.rgb
Data compression (four)-color space conversion (non-sampling version) (14)Data compression (four)-color space conversion (non-sampling version) (15)Data compression (four)-color space conversion (non-sampling version) (16)

  So far, 4:4:4 is completedRGBRGBRGBFile with 4:4:4YUVYUVYUVConversion between files.

Data compression (four)-color space conversion (non-sampling version) (2024)

FAQs

What is 4 4 4 color sampling? ›

Full color depth is usually referred to as 4:4:4. The first number indicates that there are four pixels across, the second indicates that there are four unique colors, and the third indicates that there are four changes in color for the second row.

What is 4 color format? ›

The "four-color" in "four-color printing" refers to the four ink colors—cyan, magenta, yellow, and black (CMYK)—used in offset printing presses and many digital presses. These four colors are combined to make a wider range of colors.

What is colorspace conversion? ›

Color space conversion is the translation of the representation of a color from one basis to another. This typically occurs in the context of converting an image that is represented in one color space to another color space, the goal being to make the translated image look as similar as possible to the original.

What is the difference between YUV and RGB? ›

As we know, RGB stands for red, blue and green and YUV stands for (Y) luma, or brightness, (U) blue projection and (V) red projection. HSL stands for (H) hue, (S) saturation, and L (lightness) and CMYK stands for (C ) cyan, (M) magenta, (Y) yellow and (K) black. Still with us?

What is the difference between YCbCr 4.4 4 and RGB 4.4 4? ›

There's basically no difference between RGB 4:4:4 and YCbCr 4:4:4 IF the latter option supports full range. When it doesn't, you're limited to a color ramp of 16-235 vs 0-255. But, you'll always want to use RGB on computer monitors because it's been the standard since forever.

Which is better, 4 4 4 or 4 2 2? ›

4:4:4 is uncompressed and therefore provides the best image quality, whereas 4:2:2 and 4:2:0 sacrifice color quality for lower data rate. Chroma subsampling is a type of color compression that reduces data rate and file size.

Is 4 color process the same as CMYK? ›

These four colors are Cyan, Magenta, Yellow, and Black, Which are known collectively as CMYK. In fact, 4-Color Process printing is frequently referred to as CMYK printing.

How does 4 color process work? ›

As the name implies, four color printing utilizes four colors – Cyan, Magenta, Yellow, and Black – that are applied in different concentrations on the paper. This is also known as CMYK printing, and it's most commonly used for full-color print jobs.

What is the 4 color rule? ›

In mathematics, the four color theorem, or the four color map theorem, states that no more than four colors are required to color the regions of any map so that no two adjacent regions have the same color.

How does color conversion work? ›

Color space conversion is what happens when a Color Management Module (CMM) translates color from one device's space to another. Conversion may require approximations in order to preserve the image's most important color qualities.

What color space should I use? ›

For digital uses, such as posting on social media or displaying on your smartphone, sRGB is always going to be a safe bet. For photo printing, sRGB is usually a good choice, but some high-quality print labs use Adobe RGB for printing.

What is the difference between color format and color space? ›

What's the difference between a color model and a color space? A color model is a system used to describe a color. For example with Red, Green and Blue (RGB) elements or Cyan, Magenta, Yellow and Black (CMYK). A color space is a way of mapping real colors to the color model's particular values.

What's the advantage of using Yuv color space? ›

Benefits of YUV

The color television signal carries the chroma information (U and V) superimposed onto the luma signal. Black-and-white televisions ignore the chroma and display the combined signal as a grayscale image. (The signal is designed so that the chroma does not significantly interfere with the luma signal.)

Is JPEG YUV or RGB? ›

The vast majority of images are jpegs, which are internally 420 YUV, but they get converted to 32 bit RGB for use in apps.

What does 4 4 4 mean? ›

4:4:4 may refer to: Digital images or video in which all color components have the same sampling rate, thus not using chroma subsampling. Another name for the RGB color space.

What does full color 4 4 4 mean? ›

4:4:4 is a color and luminance sub-sampling system. 4:4:4 means that there is no color sub-sampling happening. Raw can either mean a particular format (CinemaDNG RAW, RED, etc.) or it can be used as a general term to describe images that are not processed in the camera.

What is the 4 4 4 test pattern? ›

The Extron 4:4:4 Test Pattern is an indispensable tool you can use to determine the color processing performance of your system. To ensure the best quality image, Extron scalers utilize 4:4:4 chroma processing which provides the most accurate reproduction of fine color detail.

What is the 4 4-color process? ›

Because the CMYK printing process uses four ink colors, it is commonly known as 4-Color Printing. Hence, 4/4 means the face of a sheet (side one) and the reverse of a sheet (side two) are both printed with the 4 ink colors of CMYK.

What is 4 4 4 true color? ›

A true-color video signal (4:4:4) includes all of the red, green, and blue color information of each pixel. In a 24-bit system, there are 8 pixels for each color and thus 24 bits in true color. Chroma subsampling reduces file size by removing color.

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