图像有损压缩需先转换色域，避免色位或色域错乱。适合计算机显示器的为YCrCb或YCbCr，jpg采用的是这一标准，H264色域YUV也是采用的YCbCr标准。YCrCb具有色域宽，转换损失小的特点。这里采用的是RGB888格式，转换为YCrCb，再转换为RGB888格式，或YCrCb转换为RGB888格式。通过相互转换，验证理解算式。

1. 源文件

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------

float Od299 = 0.299; float Od587 = 0.587; float Od114 = 0.114;
float Od4187 = 0.4187; float Od0813 = 0.0813;
float NOd1687 = -0.1687; float Od3313 = 0.3313;
float Od5 = 0.5;  float fv128 = 128;

float Id402 = 1.402; float Id772 = 1.772;
float Od34414 = 0.34414; float Od71414 = 0.71414;

void __fastcall TForm1::SpeedButton1Click(TObject *Sender)//分解
{
   float fR,fG,fB,fY,fCr,fCb;

   // 输入RGB
   fR = (float)Edit1->Text.ToInt();
   fG = (float)Edit2->Text.ToInt();
   fB = (float)Edit3->Text.ToInt();

   // 分解
   fY = Od299 * fR + Od587 * fG + Od114 * fB;  // Y = (0.299 * R) + (0.587 * G) + (0.114 * B)
   fCb = NOd1687 * fR - Od3313 * fG + Od5 * fB + fv128;// Cb = (-0.1687 * R) - (0.3313 * G) + (0.5 * B) + 128
   fCr = Od5 * fR - Od4187 * fG - Od0813 * fB + fv128; // Cr = (0.5 * R) - (0.4187 * G) - (0.0813 * B) + 128

   // 显示
   Edit4->Text = IntToStr((int)fY);
   Edit5->Text = IntToStr((int)fCr);
   Edit6->Text = IntToStr((int)fCb);
}
//---------------------------------------------------------------------------

void __fastcall TForm1::SpeedButton2Click(TObject *Sender)//合成
{
    float fR,fG,fB,fY,fCr,fCb;

    // 输入Y,Cr,Cb
    fY = (float)Edit4->Text.ToInt();
    fCr = (float)Edit5->Text.ToInt();
    fCb = (float)Edit6->Text.ToInt();

    // 合成
    fR = fY + (Id402 * (fCr - fv128)); // R = Y + (1.402 * (Cr - 128))
    fG = fY - (Od34414 * (fCb - fv128)) - (Od71414 * (fCr - fv128)); // G = Y - (0.34414 * (Cb - 128)) - (0.71414 * (Cr - 128))
    fB = fY + (Id772 * (fCb - fv128)); // B = Y + (1.772 * (Cb - 128))

    // 显示
    Edit7->Text = FormatFloat("0", fR);
    Edit8->Text = FormatFloat("0", fG);
    Edit9->Text = FormatFloat("0", fB);
}
//---------------------------------------------------------------------------

2. 完整压缩验证文件