从RGBQUAD指针创建Magick ++图像

Question

I need to convert an RGBQUAD pointer to a Magic::Image . I tried with the code below. However, it crashes with Magick::ErrorCorruptImage

Blob blob = Blob(pBuffer, width*height*sizeof(RGBQUAD));
Image img;
img.size(Geometry(width, height));
img.magick("RGBA");
img.read(blob);

So how can I convert the RGBQUAD array to a Magick::Image?

Answer 1

I believe that the error is caused by "RGBA" format defaulting to Quantum size. Usually 16Q .

Just set the Magick::Image.depth to 8Q as RGBQUAD should be BYTE data types.

Blob blob = Blob(pBuffer, width*height*sizeof(RGBQUAD));
Image img;
img.size(Geometry(width, height));
img.depth(8);
img.magick("RGBA");
img.read(blob);

... But ... In RGBQUAD the last byte is reserved, and not an alpha channel. Quote from docs...

rgbReserved

This member is reserved and must be zero.

This would make any blob you pass to ImageMagick transparent.

I would suggest coping the data to a new buffer, and ensuring that the last byte is fully opaque.

For example...

// Note: I'm using data type `uint8_t' over `BYTE' for no particular reason.
size_t rgbquad_size = sizeof(RGBQUAD);
size_t total_bytes = width * height * rgbquad_size;
uint8_t * pCopyBuffer = new uint8_t[total_bytes];
for (size_t cursor = 0; cursor < total_bytes; ++cursor) {
    if (cursor % rgbquad_size < rgbquad_size - 1) {
        pCopyBuffer[cursor] = pBuffer[cursor];
    } else {
        pCopyBuffer[cursor] = 0xFF;
    }
}
Blob blob = Blob(pCopyBuffer, total_bytes);

Edit from comments

If pBuffer is defined as RGBQUAD * , than it would be easier to iterate over them, and assign the alpha channel value.

for (size_t cursor = 0; cursor < width*height; ++cursor)
    pBuffer[cursor].rgbReserved = 0xFF; // Set Alpha