iOS如何將RGB565的原始圖像數據轉為UIImage對象

我們在做一些圖像處理時，往往會涉及到RGB565這種圖像數據格式。由於其每個像素僅占2個字節，對於不需要像素透明度的情況下使用RGB565既能基本能保證圖像的色彩，又能降低圖像數據尺寸，節省帶寬。因此，RGB565將會是一種常用的比較經濟的圖像處理的格式。

下面就來描述一下如何在iOS中將一段RGB565的原始圖像數據轉為UIImage對象。見以下代碼：

- (UIImage*)imageFromRGB565:(void*)rawData width:(int)width height:(int)height
{
    const size_t bufferLength = width * height * 2;
    NSData *data = [NSData dataWithBytes:rawData length:bufferLength];
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGDataProviderRef provider = CGDataProviderCreateWithCFData((CFDataRef)data);
    
    // Creating CGImage from cv::Mat
    CGImageRef imageRef = CGImageCreate(width,          //width
                                        height,         //height
                                        5,              //bits per component
                                        16,             //bits per pixel
                                        width * 2,      //bytesPerRow
                                        colorSpace,     //colorspace
                                        kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder16Little,// bitmap info
                                        provider,               //CGDataProviderRef
                                        NULL,                   //decode
                                        false,                  //should interpolate
                                        kCGRenderingIntentDefault   //intent
                                        );
    
    // Getting UIImage from CGImage
    UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);
    
    return finalImage;
}

 

iOS中，QuartzCore支持的16位RGB就一種格式——AlphaNoneSkipFirst，每個分量5比特，每個像素16比特，字節序為ByteOrder16Little。因此，R分量位於低字節；而B分量位於高字節。下面舉個應用例子：

- (void)buttonTouched:(id)sender
{   
    unsigned short *imageBuffer = (unsigned short*)malloc(128 * 128 * 2);
    for(int row = 0; row < 128; row++)
    {
        unsigned short color = 0x001f;
        if(row >= 64)
            color = 0xf800;
        
        for(int col = 0; col < 128; col++)
            imageBuffer[row * 128 + col] = color;
    }
    
    UIImage *image = [self imageFromRGB565:imageBuffer width:128 height:128];
    free(imageBuffer);
    
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake((self.view.frame.size.width - 128.0f) * 0.5f, (self.view.frame.size.height - 128.0f) * 0.5f, 128.0f, 128.0f)];
    imageView.image = image;
    [self.view addSubview:imageView];
    [imageView release];
}

 

以上代碼創建了一幅128x128的RGB565的圖像，上64行為紅色；下64行為藍色。