Setting JPEG Compression Level
To specify the compression level when you save a JPEG image, initialize an
EncoderParameters structure and pass the address of that object to the function. Initialize the
EncoderParameters structure so that it has an array consisting of one
EncoderParameter structure. Initialize that one
EncoderParameter structure so that its
Value member points to a DWORD value from 0 through 100. Set the
Guid member of the
EncoderParameter structure to
$EncoderQuality.
The following console application saves three JPEG images, each with a different quality level. A quality level of 0 corresponds to the greatest compression, and a quality level of 100 corresponds to the least compression.
C++
#include <windows.h>
#include <gdiplus.h>
#include <stdio.h>
using namespace Gdiplus;
INT GetEncoderClsid(const WCHAR* format, CLSID* pClsid); // helper function
INT main()
{
// Initialize GDI+.
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
CLSID encoderClsid;
EncoderParameters encoderParameters;
ULONG quality;
Status stat;
// Get an image from the disk.
Image* image = new Image(L"Shapes.bmp");
// Get the CLSID of the JPEG encoder.
GetEncoderClsid(L"image/jpeg", &encoderClsid);
// Before we call Image::Save, we must initialize an
// EncoderParameters object. The EncoderParameters object
// has an array of EncoderParameter objects. In this
// case, there is only one EncoderParameter object in the array.
// 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.Count = 1;
encoderParameters.Parameter[0].Guid = EncoderQuality;
encoderParameters.Parameter[0].Type = EncoderParameterValueTypeLong;
encoderParameters.Parameter[0].NumberOfValues = 1;
// Save the image as a JPEG with quality level 0.
quality = 0;
encoderParameters.Parameter[0].Value = &quality;
stat = image->Save(L"Shapes001.jpg", &encoderClsid, &encoderParameters);
if(stat == Ok)
wprintf(L"%s saved successfully.\n", L"Shapes001.jpg");
else
wprintf(L"%d Attempt to save %s failed.\n", stat, L"Shapes001.jpg");
// Save the image as a JPEG with quality level 50.
quality = 50;
encoderParameters.Parameter[0].Value = &quality;
stat = image->Save(L"Shapes050.jpg", &encoderClsid, &encoderParameters);
if(stat == Ok)
wprintf(L"%s saved successfully.\n", L"Shapes050.jpg");
else
wprintf(L"%d Attempt to save %s failed.\n", stat, L"Shapes050.jpg");
// Save the image as a JPEG with quality level 100.
quality = 100;
encoderParameters.Parameter[0].Value = &quality;
stat = image->Save(L"Shapes100.jpg", &encoderClsid, &encoderParameters);
if(stat == Ok)
wprintf(L"%s saved successfully.\n", L"Shapes100.jpg");
else
wprintf(L"%d Attempt to save %s failed.\n", stat, L"Shapes100.jpg");
delete image;
GdiplusShutdown(gdiplusToken);
return 0;
}
The main function relies on the helper function
GdiPlusGetEncoderClsid to retrieve the guid of the TIFF encoder.
#COMPILE EXE
#DIM ALL
#INCLUDE "GDIPLUS.INC"
#INCLUDE "GDIPUTILS.INC"
' ========================================================================================
' Main
' ========================================================================================
FUNCTION PBMAIN
LOCAL hStatus AS LONG
LOCAL token AS DWORD
LOCAL StartupInput AS GdiplusStartupInput
LOCAL EncoderClsid AS GUID
LOCAL pImage AS DWORD
LOCAL eps AS EncoderParameters
LOCAL ep AS EncoderParameter
LOCAL dwQuality AS DWORD
LOCAL strFileName AS STRING
' // Initialize GDI+
StartupInput.GdiplusVersion = 1
hStatus = GdiplusStartup(token, StartupInput, BYVAL %NULL)
IF hStatus THEN
PRINT "Error initializing GDI+"
EXIT FUNCTION
END IF
strFileName = UCODE$("Shapes.bmp")
hStatus = GdipLoadImageFromFile(STRPTR(strFileName), pImage)
' // Get the CLSID of the JPEG encoder.
EncoderClsid = GUID$(GdiPlusGetEncoderClsid("image/jpeg"))
' // Before we call GdipSaveImageToFile, we must initialize an
' // EncoderParameters structure The EncoderParameters structure
' // has an array of EncoderParameter structures In this
' // case, there is only one EncoderParameter structure in the array.
' // The one EncoderParameter structure has an array of values.
' // In this case, there is only one value (of type DWORD)
' // in the array. We will let this value vary from 0 to 100.
eps.count = 1
eps.Parameter(0).pGuid = $EncoderQuality
eps.Parameter(0).dwType = %EncoderParameterValueTypeLong
eps.Parameter(0).NumberOfValues = 1
' // Save the image as a JPEG with quality level 0.
dwQuality = 0
eps.Parameter(0).Value = VARPTR(dwQuality)
strFileName = UCODE$("Shapes001.jpg")
hStatus = GdipSaveImageToFile(pImage, STRPTR(strFileName), EncoderClsid, eps)
IF hStatus = %StatusOk THEN PRINT "Shapes001.jpg saved successfully"
' // Save the image as a JPEG with quality level 50.
dwQuality = 50
eps.Parameter(0).Value = VARPTR(dwQuality)
strFileName = UCODE$("Shapes050.jpg")
hStatus = GdipSaveImageToFile(pImage, STRPTR(strFileName), EncoderClsid, eps)
IF hStatus = %StatusOk THEN PRINT "Shapes050.jpg saved successfully"
' // Save the image as a JPEG with quality level 100.
dwQuality = 100
eps.Parameter(0).Value = VARPTR(dwQuality)
strFileName = UCODE$("Shapes100.jpg")
hStatus = GdipSaveImageToFile(pImage, STRPTR(strFileName), EncoderClsid, eps)
IF hStatus = %StatusOk THEN PRINT "Shapes100.jpg saved successfully"
' // Cleanup
IF pImage THEN GdipDisposeImage(pImage)
' // Shutdown GDI+
GdiplusShutdown token
WAITKEY$
END FUNCTION
' ========================================================================================
This example demonstrates how to set the compression and color depth when converting an image to the TIFF format. The EncoderParameters structure has two members, a dword with the number of EncoderParameter structures and an array of EncoderParameter structures. As PowerBASIC doesn't allow structures with dynamic arrays, an alternative is to build a buffer to hold the data and pass a pointer to this buffer to the GdipSaveImageToFile function.
Example:
#COMPILE EXE
#DIM ALL
#INCLUDE "GDIPLUS.INC"
#INCLUDE "GDIPUTILS.INC"
' ========================================================================================
' Main
' ========================================================================================
FUNCTION PBMAIN
LOCAL hStatus AS LONG
LOCAL token AS DWORD
LOCAL StartupInput AS GdiplusStartupInput
LOCAL s AS STRING
LOCAL EncoderClsid AS GUID
LOCAL pImage AS DWORD
LOCAL LoadFlName AS STRING
LOCAL SaveFlName AS STRING
LOCAL ep1 AS EncoderParameter
LOCAL ep2 AS EncoderParameter
LOCAL strEncoderParameters AS STRING
LOCAL Compression AS LONG
LOCAL ColorDepth AS LONG
' --> Change as needed
LoadFlName = UCODE$("RYDER_Winona_01.jpg")
SaveFlName = UCODE$("RYDER_Winona_01.tiff")
' Fill and EncoderParameter structure with the compression
Compression = %EncoderValueCompressionLZW
ep1.pGUID = $EncoderCompression
ep1.NumberOfValues = 1
ep1.dwType = %EncoderParameterValueTypeLong
ep1.value = VARPTR(Compression)
' Fill and EncoderParameter structure wuth the color depth
ColorDepth = 24 ' 24-bits color depth
ep2.pGUID = $EncoderColorDepth
ep2.NumberOfValues = 1
ep2.dwType = %EncoderParameterValueTypeLong
ep2.value = VARPTR(ColorDepth)
' Build an EncoderParameters structure using an string
strEncoderParameters = MKDWD$(2) & ep1 & ep2
' Initialize GDI+
StartupInput.GdiplusVersion = 1
hStatus = GdiplusStartup(token, StartupInput, BYVAL %NULL)
IF hStatus THEN
MSGBOX "Error initializing GDI+"
EXIT FUNCTION
END IF
' Retrieve the encoder clsid
s = GdiPlusGetEncoderClsid("image/tiff")
IF s = "" THEN
MSGBOX "Encoder not installed"
GOTO Terminate
END IF
EncoderClsid = GUID$(s)
' Load image from file
hStatus = GdipLoadImageFromFile(STRPTR(LoadFlName), pImage)
IF hStatus THEN
MSGBOX "GdipLoadImageFromFile - Failure, status = " & STR$(hStatus)
GOTO Terminate
END IF
' Convert and save the image to file
IF pImage THEN
hStatus = GdipSaveImageToFile(pImage, STRPTR(SaveFlName), EncoderClsid, BYVAL STRPTR(strEncoderParameters))
IF hStatus THEN
MSGBOX "GdipSaveImageToFile - Failure, status = " & STR$(hStatus)
ELSE
MSGBOX "Image converted"
END IF
' Dispose the image
hStatus = GdipDisposeImage(pImage)
END IF
Terminate:
' Shutdown GDI+
GdiplusShutdown token
END FUNCTION
' ========================================================================================