列出所有编码器的参数和值

以下控制台应用程序列出了计算机上安装的各种编码器支持的所有参数。 main函数调用 GetImageEncoders 来发现可用的编码器。 对于每个可用的编码器，main函数调用帮助程序函数 ShowAllEncoderParameters。

ShowAllEncoderParameters 函数调用 Image：：GetEncoderParameterList 方法，以发现给定编码器支持的参数。 对于每个受支持的参数， 函数会列出类别、数据类型和值数。 ShowAllEncoderParameters 函数依赖于两个帮助程序函数：EncoderParameterCategoryFromGUID 和 ValueTypeFromULONG。

#include <windows.h>
#include <gdiplus.h>
#include <strsafe.h>
using namespace Gdiplus;

// Helper functions
void ShowAllEncoderParameters(ImageCodecInfo*);
HRESULT EncoderParameterCategoryFromGUID(GUID guid, WCHAR* category, UINT maxChars);
HRESULT ValueTypeFromULONG(ULONG index, WCHAR* strValueType, UINT maxChars);

INT main()
{
   // Initialize GDI+
   GdiplusStartupInput gdiplusStartupInput;
   ULONG_PTR gdiplusToken;
   GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

   UINT  num;        // Number of image encoders
   UINT  size;       // Size of the image encoder array in bytes

   ImageCodecInfo* pImageCodecInfo;

   // How many encoders are there?
   // How big (in bytes) is the array of all ImageCodecInfo objects?
   GetImageEncodersSize(&num, &size);

   // Create a buffer large enough to hold the array of ImageCodecInfo
   // objects that will be returned by GetImageEncoders.
   pImageCodecInfo = (ImageCodecInfo*)(malloc(size));

   // 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(num, size, pImageCodecInfo);
    
   // For each ImageCodecInfo object in the array, show all parameters.
   for(UINT j = 0; j < num; ++j)
   { 
      ShowAllEncoderParameters(&(pImageCodecInfo[j]));
   }

   GdiplusShutdown(gdiplusToken);
   return 0;
}


/////////////////////////////////////////////////
// Helper functions

VOID ShowAllEncoderParameters(ImageCodecInfo* pImageCodecInfo)
{
   CONST MAX_CATEGORY_LENGTH = 50;
   CONST MAX_VALUE_TYPE_LENGTH = 50;
   WCHAR strParameterCategory[MAX_CATEGORY_LENGTH] = L"";
   WCHAR strValueType[MAX_VALUE_TYPE_LENGTH] = L"";

   wprintf(L"\n\n%s\n", pImageCodecInfo->MimeType);

   // Create a Bitmap (inherited from Image) object so that we can call
   // GetParameterListSize and GetParameterList.
   Bitmap bitmap(1, 1);

   // How big (in bytes) is the encoder's parameter list?
   UINT listSize = 0; 
   listSize = bitmap.GetEncoderParameterListSize(&pImageCodecInfo->Clsid);
   printf("  The parameter list requires %d bytes.\n", listSize);

   if(listSize == 0)
      return;

   // Allocate a buffer large enough to hold the parameter list.
   EncoderParameters* pEncoderParameters = NULL;
   pEncoderParameters = (EncoderParameters*)malloc(listSize);

   if(pEncoderParameters == NULL)
      return;

   // Get the parameter list for the encoder.
   bitmap.GetEncoderParameterList(
      &pImageCodecInfo->Clsid, listSize, pEncoderParameters);

   // pEncoderParameters points to an EncoderParameters object, which
   // has a Count member and an array of EncoderParameter objects.
   // How many EncoderParameter objects are in the array?
   printf("  There are %d EncoderParameter objects in the array.\n", 
      pEncoderParameters->Count);

   // For each EncoderParameter object in the array, list the
   // parameter category, data type, and number of values.
   for(UINT k = 0; k < pEncoderParameters->Count; ++k)
   {
      EncoderParameterCategoryFromGUID(
         pEncoderParameters->Parameter[k].Guid, strParameterCategory, MAX_CATEGORY_LENGTH);

      ValueTypeFromULONG(
         pEncoderParameters->Parameter[k].Type, strValueType, MAX_VALUE_TYPE_LENGTH);

      printf("    Parameter[%d]\n", k);
      wprintf(L"      The category is %s.\n", strParameterCategory);
      wprintf(L"      The data type is %s.\n", strValueType);

      printf("      The number of values is %d.\n",
      pEncoderParameters->Parameter[k].NumberOfValues); 
   } // for

   free(pEncoderParameters);
} // ShowAllEncoderParameters


HRESULT EncoderParameterCategoryFromGUID(GUID guid, WCHAR* category, UINT maxChars)
{
   HRESULT hr = E_FAIL;

   if(guid == EncoderCompression)
      hr = StringCchCopyW(category, maxChars, L"Compression");
   else if(guid == EncoderColorDepth)
      hr = StringCchCopyW(category, maxChars, L"ColorDepth");
   else if(guid == EncoderScanMethod)
      hr = StringCchCopyW(category, maxChars, L"ScanMethod");
   else if(guid == EncoderVersion)
      hr = StringCchCopyW(category, maxChars, L"Version");
   else if(guid == EncoderRenderMethod)
      hr = StringCchCopyW(category, maxChars, L"RenderMethod");
   else if(guid == EncoderQuality)
      hr = StringCchCopyW(category, maxChars, L"Quality");
   else if(guid == EncoderTransformation)
      hr = StringCchCopyW(category, maxChars, L"Transformation");
   else if(guid == EncoderLuminanceTable)
      hr = StringCchCopyW(category, maxChars, L"LuminanceTable");
   else if(guid == EncoderChrominanceTable)
      hr = StringCchCopyW(category, maxChars, L"ChrominanceTable");
   else if(guid == EncoderSaveFlag)
      hr = StringCchCopyW(category, maxChars, L"SaveFlag");
   else
      hr = StringCchCopyW(category, maxChars, L"Unknown category");

   return hr;
} // EncoderParameterCategoryFromGUID


HRESULT ValueTypeFromULONG(ULONG index, WCHAR* strValueType, UINT maxChars)
{
   HRESULT hr = E_FAIL;

   WCHAR* valueTypes[] = {
      L"Nothing",                  // 0
      L"ValueTypeByte",            // 1
      L"ValueTypeASCII",           // 2
      L"ValueTypeShort",           // 3
      L"ValueTypeLong",            // 4
      L"ValueTypeRational",        // 5
      L"ValueTypeLongRange",       // 6
      L"ValueTypeUndefined",       // 7
      L"ValueTypeRationalRange"};  // 8

   hr = StringCchCopyW(strValueType, maxChars, valueTypes[index]);
   return hr;

} // ValueTypeFromULONG

运行上述控制台应用程序时，将获得类似于以下内容的输出：

image/bmp
  The parameter list requires 0 bytes.

image/jpeg
  The parameter list requires 172 bytes.
  There are 4 EncoderParameter objects in the array.
    Parameter[0]
      The category is Transformation.
      The data type is Long.
      The number of values is 5.
    Parameter[1]
      The category is Quality.
      The data type is LongRange.
      The number of values is 1.
    Parameter[2]
      The category is LuminanceTable.
      The data type is Short.
      The number of values is 0.
    Parameter[3]
      The category is ChrominanceTable.
      The data type is Short.
      The number of values is 0.

image/gif
  The parameter list requires 0 bytes.

image/tiff
  The parameter list requires 160 bytes.
  There are 3 EncoderParameter objects in the array.
    Parameter[0]
      The category is Compression.
      The data type is Long.
      The number of values is 5.
    Parameter[1]
      The category is ColorDepth.
      The data type is Long.
      The number of values is 5.
    Parameter[2]
      The category is SaveFlag.
      The data type is Long.
      The number of values is 1.

image/png
  The parameter list requires 0 bytes.

可以通过检查前面的程序输出来得出以下结论：

• JPEG 编码器支持 Transformation、Quality、LuminanceTable 和 ChrominanceTable 参数类别。
• TIFF 编码器支持 Compression、ColorDepth 和 SaveFlag 参数类别。

还可以查看每个参数类别的可接受值数。 例如，可以看到 ColorDepth 参数类别 (TIFF 编解码器) 有五个 ULONG 类型的值。 以下代码列出了这五个值。 假设 pEncoderParameters 是指向表示 TIFF 编码器 的 EncoderParameters 对象的指针。

ULONG* pUlong = (ULONG*)(pEncoderParameters->Parameter[1].Value);
ULONG numVals = pEncoderParameters->Parameter[1].NumberOfValues;
printf("\nThe allowable values for ColorDepth are\n");

for(ULONG k = 0; k < numVals; ++k)
{
   printf("  %u\n", pUlong[k]);
}
            

前面的代码产生以下输出：

The allowable values for ColorDepth are
  1
  4
  8
  24
  32
            

如果编写类似于上述示例的代码来调查其他参数类别的允许值，将获得如下所示的结果。