今天同事向我询问图片压缩的算法，我想起大概两三年前做过的一个项目。其中包含了尺寸和质量两种压缩算法，并且支持JPEG、bmp、PNG等格式。今天把这段逻辑贴出来，供大家参考。
尺寸压缩
bool CompressImagePixel(
const WCHAR* pszOriFilePath,
const WCHAR* pszDestFilePah,
UINT ulNewHeigth,
UINT ulNewWidth )
{
// Initialize GDI+.
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
Status stat = GenericError;
stat = GdiplusStartup( &gdiplusToken, &gdiplusStartupInput, NULL );
if ( Ok != stat ) {
return false;
}
// 重置状态
stat = GenericError;
// Get an image from the disk.
Image* pImage = new Image(pszOriFilePath);do {
if ( NULL == pImage ) {
break;
}// 获取长宽
UINT unOriHeight = pImage->GetHeight();
UINT unOriWidth = pImage->GetWidth();do {
CLSID encoderClsid;
if ( unOriWidth < 1 || unOriHeight < 1 ) {
break;
}// Get the CLSID of the JPEG encoder.
if ( !GetEncoderClsid(L"image/jpeg", &encoderClsid) ) {
break;
}REAL fSrcX = 0.0f;
REAL fSrcY = 0.0f;
REAL fSrcWidth = (REAL) unOriWidth;
REAL fSrcHeight = (REAL) unOriHeight ;
RectF RectDest( 0.0f, 0.0f, (REAL)ulNewWidth, (REAL)ulNewHeigth);Bitmap* pTempBitmap = new Bitmap( ulNewWidth, ulNewHeigth );
Graphics* graphics = NULL;do {
if ( !pTempBitmap ) {
break;
}graphics = Graphics::FromImage( pTempBitmap );
if ( !graphics ) {
break;
}stat = graphics->SetInterpolationMode(Gdiplus::InterpolationModeHighQuality);
if ( Ok != stat ) {
break;
}stat = graphics->SetSmoothingMode(Gdiplus::SmoothingModeHighQuality);
if ( Ok != stat ) {
break;
}stat = graphics->DrawImage( pImage, RectDest, fSrcX, fSrcY, fSrcWidth, fSrcHeight,
UnitPixel, NULL, NULL, NULL);
if ( Ok != stat ) {
break;
}stat = pTempBitmap->Save( pszDestFilePah, &encoderClsid, NULL );
if ( Ok != stat ) {
break;
}} while(0);
if ( NULL != graphics ) {
delete graphics;
graphics = NULL;
}if ( NULL != pTempBitmap ) {
delete pTempBitmap;
pTempBitmap = NULL;
}
} while(0);
} while (0);if ( pImage ) {
delete pImage;
pImage = NULL;
}GdiplusShutdown(gdiplusToken);
return ( ( Ok == stat ) ? true : false );
}
质量压缩
bool CompressImageQuality(
const WCHAR* pszOriFilePath,
const WCHAR* pszDestFilePah,
ULONG quality )
{
// copy from http://msdn.microsoft.com/en-us/library/ms533844(v=VS.85).aspx
// Initialize GDI+.
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
Status stat = GenericError;
stat = GdiplusStartup( &gdiplusToken, &gdiplusStartupInput, NULL );
if ( Ok != stat ) {
return false;
}// 重置状态
stat = GenericError;// Get an image from the disk.
Image* pImage = new Image(pszOriFilePath);do {
if ( NULL == pImage ) {
break;
}// 获取长宽
UINT ulHeight = pImage->GetHeight();
UINT ulWidth = pImage->GetWidth();
if ( ulWidth < 1 || ulHeight < 1 ) {
break;
}// Get the CLSID of the JPEG encoder.
CLSID encoderClsid;
if ( !GetEncoderClsid(L"image/jpeg", &encoderClsid) ) {
break;
}// The one EncoderParameter object has an array of values.
// In this case, there is only one value (of type ULONG)
// in the array. We will let this value vary from 0 to 100.
EncoderParameters encoderParameters;
encoderParameters.Count = 1;
encoderParameters.Parameter[0].Guid = EncoderQuality;
encoderParameters.Parameter[0].Type = EncoderParameterValueTypeLong;
encoderParameters.Parameter[0].NumberOfValues = 1;
encoderParameters.Parameter[0].Value = &quality;
stat = pImage->Save(pszDestFilePah, &encoderClsid, &encoderParameters);
} while(0);if ( pImage ) {
delete pImage;
pImage = NULL;
}GdiplusShutdown(gdiplusToken);
return ( ( stat == Ok ) ? true : false );
}
这两个算法，都关联了一个函数GetEncoderClsid，其实现是：
#include <Windows.h>
#include <GdiPlus.h>
#pragma comment( lib, "GdiPlus.lib" )
using namespace Gdiplus;bool GetEncoderClsid(const WCHAR* pszFormat, CLSID* pClsid)
{
UINT unNum = 0; // number of image encoders
UINT unSize = 0; // size of the image encoder array in bytesImageCodecInfo* pImageCodecInfo = NULL;
// How many encoders are there?
// How big (in bytes) is the array of all ImageCodecInfo objects?
GetImageEncodersSize( &unNum, &unSize );
if ( 0 == unSize ) {
return false; // Failure
}// Create a buffer large enough to hold the array of ImageCodecInfo
// objects that will be returned by GetImageEncoders.
pImageCodecInfo = (ImageCodecInfo*)( malloc(unSize) );
if ( !pImageCodecInfo ) {
return false; // Failure
}// GetImageEncoders creates an array of ImageCodecInfo objects
// and copies that array into a previously allocated buffer.
// The third argument, imageCodecInfos, is a pointer to that buffer.
GetImageEncoders( unNum, unSize, pImageCodecInfo );for ( UINT j = 0; j < unNum; ++j ) {
if ( wcscmp( pImageCodecInfo[j].MimeType, pszFormat ) == 0 ) {
*pClsid = pImageCodecInfo[j].Clsid;
free(pImageCodecInfo);
pImageCodecInfo = NULL;
return true; // Success
}
}free( pImageCodecInfo );
pImageCodecInfo = NULL;
return false; // Failure
}
在我的测试代码中，文件名中包含A的为源文件，文件名中包含B的是尺寸压缩算法得到的文件，文件名中包含C的是质量压缩（尺寸不变）算法得到的文件。测试代码是:
int _tmain(int argc, _TCHAR* argv[])
{
CompressImagePixel( L"1A.jpg", L"1B.jpg", 100, 100 );
CompressImageQuality( L"1A.jpg", L"1C.jpg", 30 );CompressImagePixel( L"2A.png", L"2B.jpg", 100, 100 );
CompressImageQuality( L"2A.png", L"2C.jpg", 30 );CompressImagePixel( L"3A.bmp", L"3B.jpg", 100, 100 );
CompressImageQuality( L"3A.bmp", L"3C.jpg", 30 );
return 0;
}
其压缩结果是
从压缩结果看，尺寸压缩是稳定的，质量压缩是不稳定的。如果想通过压缩算法控制文件大小，需要结合这两种方法。但是需要指出的是，该质量压缩算法不可以滥用。因为在一定情况下，该质量压缩会使文件空间大小变大。
最后附上工程代码。
作者：方亮
