Converting a kCVPixelFormatType_420YpCbCr8BiPlanarFullRange buffer to a RGB buffer creates a bluish picture

Question

I'm trying to convert a kCVPixelFormatType_420YpCbCr8BiPlanarFullRange to RGB so I can save the image in a JPG file, this is the code I'm using:

#define clamp(a) (a>255?255:(a<0?0:a));

- (UIImage *)makeUIImage:(uint8_t *)inBaseAddress bufferInfo:(CVPlanarPixelBufferInfo_YCbCrBiPlanar *)inBufferInfo width:(size_t)inWidth height:(size_t)inHeight bytesPerRow:(size_t)inBytesPerRow
{
    NSUInteger yOffset = EndianU32_BtoN(inBufferInfo->componentInfoY.offset);
    NSUInteger yPitch = EndianU32_BtoN(inBufferInfo->componentInfoY.rowBytes);

    NSUInteger cbCrOffset = EndianU32_BtoN(inBufferInfo->componentInfoCbCr.offset);
    NSUInteger cbCrPitch = EndianU32_BtoN(inBufferInfo->componentInfoCbCr.rowBytes);

    uint8_t *rgbBuffer = malloc(inWidth * inHeight * 4);
    uint8_t *yBuffer = inBaseAddress + yOffset;
    uint8_t *cbCrBuffer = inBaseAddress + cbCrOffset;

    for(int y = 0; y < inHeight; y++)
    {
        uint8_t *rgbBufferLine = &rgbBuffer[y * inWidth * 4];
        uint8_t *yBufferLine = &yBuffer[y * yPitch];
        uint8_t *cbCrBufferLine = &cbCrBuffer[(y >> 1) * cbCrPitch];

        for(int x = 0; x < inWidth; x++)
        {
            uint8_t y = yBufferLine[x];
            uint8_t cb = cbCrBufferLine[x & ~1];
            uint8_t cr = cbCrBufferLine[x | 1];

            uint8_t *rgbOutput = &rgbBufferLine[x*4];

            int r = (int)round( (y - 16) * 1.164 + (cr - 128) *  1.596 );
            int g = (int)round( (y - 16) * 1.164 + (cb - 128) * -0.391 + (cr - 128) * -0.813 );
            int b = (int)round( (y - 16) * 1.164 + (cb - 128) *  2.018 );

            rgbOutput[0] = 0xff;
            rgbOutput[1] = clamp(r);
            rgbOutput[2] = clamp(g);
            rgbOutput[3] = clamp(b);

        }
    }

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(rgbBuffer, yPitch, inHeight, 8,
                                                 yPitch*4, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);

    CGImageRef quartzImage = CGBitmapContextCreateImage(context);

    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    CGImageRelease(quartzImage);
    free(rgbBuffer);
    return  image;
}

-(void)createImg:(CMSampleBufferRef) sampleBuffer index:(int)index
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);

    //Lock the imagebuffer
    CVPixelBufferLockBaseAddress(imageBuffer,0);

    // Get information about the image
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);

    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);

    CVPlanarPixelBufferInfo_YCbCrBiPlanar *bufferInfo = (CVPlanarPixelBufferInfo_YCbCrBiPlanar *)baseAddress;

    baseAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);


    // convert the image
    UIImage *img = [self makeUIImage:baseAddress bufferInfo:bufferInfo width:width height:height bytesPerRow:bytesPerRow];
    NSString *videoThumbPath = [NSString
                                stringWithFormat:@"%@/img%02d.jpg",
                                burstFolderPath,
                                index];

    NSData *imageData = [NSData dataWithData:UIImageJPEGRepresentation(img,0.8f)];
    [imageData writeToFile:videoThumbPath atomically:YES];
}

The image is generated but the colours are wrong, the picture is bluish,and furthermore I seem to have a break at right side of the picture: enter image description here

What am I doing wrong?

First, it's really hard to tell anything from your picture. We have no frame of reference for what it's supposed to look like. What did the original look like? Second - does [this question and answer](http://stackoverflow.com/questions/7041172/pils-colour-space-conversion-ycbcr-rgb?rq=1) help at all? — user1118321, Jun 09 '14 at 04:35
You probably should convert image in some app and include it here as expected result. — Timur Kuchkarov, Aug 28 '14 at 09:54

score 2 · Answer 1 · answered Aug 28 '14 at 09:30

// Hope it can help someone!

int bytesPerPixel = 4;

uint8_t *rgbBuffer = (uint8_t *)malloc(width * height * bytesPerPixel);

for(int y = 0; y < height; y++)
{
    uint8_t *rgbBufferLine = &rgbBuffer[y * width * bytesPerPixel];
    uint8_t *yBufferLine = &yBuffer[y * yPitch];
    uint8_t *cbCrBufferLine = &cbCrBuffer[(y >> 1) * cbCrPitch];

    for(int x = 0; x < width; x++)
    {
        int16_t y = yBufferLine[x];
        int16_t cb = cbCrBufferLine[x & ~1] - 128;
        int16_t cr = cbCrBufferLine[x | 1] - 128;

        uint8_t *rgbOutput = &rgbBufferLine[x*bytesPerPixel];

        int16_t r = (int16_t)roundf( y + cr *  1.4 );
        int16_t g = (int16_t)roundf( y + cb * -0.343 + cr * -0.711 );
        int16_t b = (int16_t)roundf( y + cb *  1.765);

        //ABGR
        rgbOutput[0] = 0xff;
        rgbOutput[1] = clamp(b);
        rgbOutput[2] = clamp(g);
        rgbOutput[3] = clamp(r);
    }
}

Converting a kCVPixelFormatType_420YpCbCr8BiPlanarFullRange buffer to a RGB buffer creates a bluish picture

1 Answers1