Create CImage from Byte array

问题:

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.

回答1:

CImage supports DIBs quite neatly and has a SetPixel() method so you could presumably do something like this (uncompiled, untested code ahead!):

CImage img;
img.Create(width, height, 24 /* bpp */, 0 /* No alpha channel */);

int nPixel = 0;
for(int row = 0; row < height; row++)
{
    for(int col = 0; col < width; col++)
    {
        BYTE r = imgBits[nPixel++];
        BYTE g = imgBits[nPixel++];
        BYTE b = imgBits[nPixel++];
        img.SetPixel(row, col, RGB(r, g, b));
    }
}

Maybe not the most efficient method but I should think it is the simplest approach.

回答2:

Use memcpy to copy the data, then SetDIBits or SetDIBitsToDevice depending on what you need to do. Take care though, the scanlines of the raw image data are aligned on 4-byte boundaries (IIRC, it's been a few years since I did this) so the data you get back from GetDIBits will never be exactly the same as the original data (well it might, depending on the image size).

So most likely you will need to memcpy scanline by scanline.

回答3:

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;

回答4:

Here is a simpler solution. You can use GetPixelAddress(...) instead of all this BITMAPHEADERINFO and SedDIBitsToDevice. Another problem I have solved was with 8-bit images, which need to have the color table defined.

CImage outImage;
outImage.Create(width, height, channelCount * 8);

int lineSize = width * channelCount;
if (channelCount == 1)
{
    // Define the color table
    RGBQUAD* tab = new RGBQUAD[256];
    for (int i = 0; i < 256; ++i)
    {
        tab[i].rgbRed = i;
        tab[i].rgbGreen = i;
        tab[i].rgbBlue = i;
        tab[i].rgbReserved = 0;
    }
    outImage.SetColorTable(0, 256, tab);
    delete[] tab;
}

// Copy pixel values
// Warining: does not convert from RGB to BGR
for ( int i = 0; i < height; i++ )
{
    void*       dst = outImage.GetPixelAddress(0, i);
    const void* src = /* put the pointer to the i'th source row here */;
    memcpy(dst, src, lineSize);
}