- (CGContextRef) RFS_blackAndWhiteImageContextOfWidth:(int)pixelsWidth andHeight:(int)pixelsHeight
{
    CGContextRef theContext=NULL;
    CGColorSpaceRef colorSpace;
    void *bitmapData;
    int bitmapByteCount;
    int bitmapBytePerRow;

    bitmapBytePerRow = pixelsWidth;
    bitmapByteCount = (bitmapBytePerRow * pixelsHeight);

    colorSpace = CGColorSpaceCreateDeviceGray();
    bitmapData = malloc(bitmapByteCount);

    if(bitmapData == NULL) {
        printf("Error");
        return NULL;
    }

    theContext = CGBitmapContextCreate(bitmapData,
                                       pixelsWidth,
                                       pixelsHeight,
                                       8,
                                       bitmapBytePerRow,
                                       colorSpace,
                                       kCGImageAlphaNoneSkipLast);

    if(theContext == NULL) {
        free(bitmapData);
        printf("ERROR");
        return NULL;
    }
}

// get error: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 16 bits/pixel; 1-component color space; kCGImageAlphaNoneSkipLast; 320 bytes/row.