EncoderTransformation ignored, no errors produced.
- From: "jason.cipriani@xxxxxxxxx" <jason.cipriani@xxxxxxxxx>
- Date: Thu, 13 Mar 2008 22:58:13 -0700 (PDT)
I have some uncompressed image data in memory that is vertically
flipped, and I would like to use GDI+ to save it as a JPEG image, and
I would also like to use the EncoderTransformation encoder parameter
to vertically flip the saved image.
At the end of this post is the source code for a simple console app I
wrote to test this; the entire VS2005 project is also available here
(sorry, Google Groups does not allow attachments here):
http://www.sendspace.com/file/300z1r
The code creates a test image in memory -- a 160x160 image with a
white pixel at (30,30). It then creates a Gdiplus::Bitmap using that
image data, and writes out two jpeg files:
fliptest-identity.jpg with no transformation,
fliptest-vertflip.jpg vertically flipped.
I have two questions:
1) The two output images are identical, and vertical flipping is
being ignored. Why?
2) What is the correct way to allocate space for EncoderParameters
(in that code I use placement new into a buffer that's probably big
enough to hold all the parameters).
Question 1 has been frustrating me; the JPEG is written with no errors
but the EncoderTransformation parameter is ignored. It does not matter
if I change the order of the parameters.
Thanks,
Jason
------ fliptest.cpp ------
#include <windows.h>
#include <gdiplus.h>
#include <stdio.h>
#include <new>
using namespace Gdiplus;
// straight from MSDN example docs
static int GetEncoderClsid(const WCHAR* format, CLSID* pClsid)
{
UINT num = 0; // number of image encoders
UINT size = 0; // size of the image encoder array in bytes
ImageCodecInfo* pImageCodecInfo;
GetImageEncodersSize(&num, &size);
if(size == 0)
return -1; // Failure
pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
if(pImageCodecInfo == NULL)
return -1; // Failure
GetImageEncoders(num, size, pImageCodecInfo);
for(UINT j = 0; j < num; ++j) {
if( wcscmp(pImageCodecInfo[j].MimeType, format) == 0 ) {
*pClsid = pImageCodecInfo[j].Clsid;
free(pImageCodecInfo);
return j; // Success
}
}
free(pImageCodecInfo);
return -1; // Failure
}
// write JPEG; possibly flip vertically.
void SaveJPEG (Bitmap *b, const WCHAR *filename, bool vflip) {
CLSID encoderClsid;
ULONG quality, depth, transform;
Status st;
int index;
// encparams is big enough for 3 encoder parameters i'm assuming.
// question 1: what's the right way to do this?
char encparams[2000];
EncoderParameters *encoderParameters = new (encparams)
EncoderParameters;
// Get the CLSID of the JPEG encoder.
index = GetEncoderClsid(L"image/jpeg", &encoderClsid);
if (index == -1) {
printf("GetEncoderClsid() failed.\n");
return;
}
// Set encoder options, vertical flip if requested.
encoderParameters->Count = vflip ? 3 : 2;
quality = 100;
encoderParameters->Parameter[0].Guid = EncoderQuality;
encoderParameters->Parameter[0].Type = EncoderParameterValueTypeLong;
encoderParameters->Parameter[0].NumberOfValues = 1;
encoderParameters->Parameter[0].Value = &quality;
depth = 24;
encoderParameters->Parameter[1].Guid = EncoderColorDepth;
encoderParameters->Parameter[1].Type = EncoderParameterValueTypeLong;
encoderParameters->Parameter[1].NumberOfValues = 1;
encoderParameters->Parameter[1].Value = &depth;
if (vflip) {
// question 2: why is this ignored?
transform = EncoderValueTransformFlipVertical;
encoderParameters->Parameter[2].Guid = EncoderTransformation;
encoderParameters->Parameter[2].Type =
EncoderParameterValueTypeLong;
encoderParameters->Parameter[2].NumberOfValues = 1;
encoderParameters->Parameter[2].Value = &transform;
}
// Write.
st = b->Save(filename, &encoderClsid, encoderParameters);
printf("%ls: %s\n", filename, (st == Ok) ? "OK" : "FAIL");
// from placement new
encoderParameters->~EncoderParameters();
}
int main (int, char **) {
GdiplusStartupInput _gdiplusStartupInput;
ULONG_PTR _gdiplusToken;
GdiplusStartup(&_gdiplusToken, &_gdiplusStartupInput, NULL);
// create test Bitmap, black with a white pixel at (30,30).
unsigned char data[160][160][3];
memset(data, 0, sizeof(data));
data[30][30][0] = 255;
data[30][30][1] = 255;
data[30][30][2] = 255;
Bitmap *img = new Bitmap(160, 160, 3 * 160, PixelFormat24bppRGB,
(BYTE *)data);
// save as jpeg, no transformation
SaveJPEG(img, L"fliptest-identity.jpg", false);
// save as jpeg, vertically flipped.
SaveJPEG(img, L"fliptest-vertflip.jpg", true);
delete img;
GdiplusShutdown(_gdiplusToken);
getchar();
return 0;
}
.
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