Forcing to WIC to treat image data as RGB

Question

I have a image as a BYTE array(in RGB format) and I needed to encode it. I did, but colors have changed.

/*Create stream and initialized*/
hr = piFactory->CreateStream(&piStream);
hr = piStream->InitializeFromFilename(L"..\\test.jpg",GENERIC_WRITE);

/*created an encoder. I want to save JPG*/
hr = piFactory->CreateEncoder(GUID_ContainerFormatJpeg, NULL, &piEncoder);

did some manipulations, also tried to set pixel format.

hr = piBitmapFrame->SetPixelFormat(&formatGUID);

but it always set to "GUID_WICPixelFormat24bppBGR"

and i write image data as here.

/*pBitmap contains image data*/
hr = piBitmapFrame->WritePixels(lHeight, cbStride, cbBufferSize, pBitmap);

the problem was colors of the image has changed, and I found that if i change RGB to BGR then the output looks fine. so i did this

   for(int i = 0; i < DataSize; i += 3)
    {
        inBuff[i] = pBitmap[i+2];
        inBuff[i + 1] = pBitmap[i+1];
        inBuff[i + 2] = pBitmap[i];
    }

    pBitmap = inBuff

But i dont want to expend more time here looping through whole image. I need to tell WIC "treat the data as RGB(or BGR)".

is that possible? if it is then how?

Answer 1

You can create a bitmap first. at that time you could say the format it needs to be. Here is "24bppRGB" format:

    hr = piFactory->CreateBitmapFromMemory(
        lWidth,
        lHeight,
        GUID_WICPixelFormat24bppRGB,
        cbStride,
        cbBufferSize,
        pBitmap,
        &piBitmapSrc
        );

This is how You write image data into the frame:

hr = piBitmapFrame->WritePixels(lHeight, cbStride, cbBufferSize, pBitmap);

Instead write image to the frame like this (because WritePixels() doesn't accept bitmap):

    hr = piBitmapFrame->WriteSource(
        piBitmapSrc,
        NULL
        );

And that help to avoid the loop. I'm not sure what happens inside the CreateBitmapFromMemory() though. Since you are concerned with time, I don't know if this will help (it still makes your code better).