Question

I need to create a CImage from a byte array (actually, its an array of unsigned char, but I can cast to whatever form is necessary). The byte array is in the form “RGBRGBRGB…”. The new image needs to contain a copy of the image bytes, rather than using the memory of the byte array itself.

I have tried many different ways of achieving this — including going through various HBITMAP creation functions, trying to use BitBlt — and nothing so far has worked.

To test whether the function works, it should pass this test:

BYTE* imgBits;
int width;
int height;
int Bpp;   // BYTES per pixel (e.g. 3)
getImage(&imgBits, &width, &height, &Bpp); // get the image bits

// This is the magic function I need!!!
CImage img = createCImage(imgBits, width, height, Bpp);

// Test the image
BYTE* data = img.GetBits();  // data should now have the same data as imgBits

All implementations of createCImage() so far have ended up with data pointing to an empty (zero filled) array.

Answer 1

Thanks everyone, I managed to solve it in the end with your help. It mainly involved @tinman and @Roel’s suggestion to use SetDIBitsToDevice(), but it involved a bit of extra bit-twiddling and memory management, so I thought I’d share my end-point here.

In the code below, I assume that width, height and Bpp (Bytes per pixel) are set, and that data is a pointer to the array of RGB pixel values.

// Create the header info
bmInfohdr.biSize = sizeof(BITMAPINFOHEADER);
bmInfohdr.biWidth = width;
bmInfohdr.biHeight = -height;
bmInfohdr.biPlanes = 1;
bmInfohdr.biBitCount = Bpp*8;
bmInfohdr.biCompression = BI_RGB;
bmInfohdr.biSizeImage = width*height*Bpp;
bmInfohdr.biXPelsPerMeter = 0;
bmInfohdr.biYPelsPerMeter = 0;
bmInfohdr.biClrUsed = 0;
bmInfohdr.biClrImportant = 0;

BITMAPINFO bmInfo;
bmInfo.bmiHeader = bmInfohdr;
bmInfo.bmiColors[0].rgbBlue=255;

// Allocate some memory and some pointers
unsigned char * p24Img = new unsigned char[width*height*3];
BYTE *pTemp,*ptr;
pTemp=(BYTE*)data;
ptr=p24Img;

// Convert image from RGB to BGR
for (DWORD index = 0; index < width*height ; index++)
{
    unsigned char r = *(pTemp++);
    unsigned char g = *(pTemp++);
    unsigned char b = *(pTemp++);   

    *(ptr++) = b;
    *(ptr++) = g;
    *(ptr++) = r;
}

// Create the CImage
CImage im;
im.Create(width, height, 24, NULL);

HDC dc = im.GetDC();
SetDIBitsToDevice(dc, 0,0,width,height,0,0, 0, height, p24Img, &bmInfo, DIB_RGB_COLORS);
im.ReleaseDC();

delete[] p24Img;