如何在 iPhone 相机预览窗口中动态更改像素颜色？

Question

我正在使用 UIImagePickerController 在 iPhone 上拍照。我想即时调整照片，看来我可以使用 UIImagePickerController 即时调整照片的形状，但我无法找到即时更改颜色的方法。例如，将所有颜色更改为黑/白。

谢谢。

Answer 1

最好的方法是使用 AVCaptureSession 对象。我正在做你在我的免费应用程序“Live Effects Cam”中所说的事情

，网上有几个代码示例，它们也可以帮助你实现这一点。以下是可能有帮助的示例代码块：

- (void) activateCameraFeed
    {
    videoSettings = nil;

#if USE_32BGRA
    pixelFormatCode = [[NSNumber alloc] initWithUnsignedInt:(unsigned int)kCVPixelFormatType_32BGRA];
    pixelFormatKey = [[NSString alloc] initWithString:(NSString *)kCVPixelBufferPixelFormatTypeKey];
    videoSettings = [[NSDictionary alloc] initWithObjectsAndKeys:pixelFormatCode, pixelFormatKey, nil]; 
#endif

    videoDataOutputQueue = dispatch_queue_create("com.jellyfilledstudios.ImageCaptureQueue", NULL);

    captureVideoOutput = [[AVCaptureVideoDataOutput alloc] init];
    [captureVideoOutput setAlwaysDiscardsLateVideoFrames:YES]; 
    [captureVideoOutput setSampleBufferDelegate:self queue:videoDataOutputQueue];
    [captureVideoOutput setVideoSettings:videoSettings];
    [captureVideoOutput setMinFrameDuration:kCMTimeZero];

    dispatch_release(videoDataOutputQueue); // AVCaptureVideoDataOutput uses dispatch_retain() & dispatch_release() so we can dispatch_release() our reference now

    if ( useFrontCamera )
        {
        currentCameraDeviceIndex = frontCameraDeviceIndex;
        cameraImageOrientation = UIImageOrientationLeftMirrored;
        }
    else
        {
        currentCameraDeviceIndex = backCameraDeviceIndex;
        cameraImageOrientation = UIImageOrientationRight;
        }

    selectedCamera = [[AVCaptureDevice devices] objectAtIndex:(NSUInteger)currentCameraDeviceIndex];

    captureVideoInput = [AVCaptureDeviceInput deviceInputWithDevice:selectedCamera error:nil];

    captureSession = [[AVCaptureSession alloc] init];

    [captureSession beginConfiguration];

    [self setCaptureConfiguration];

    [captureSession addInput:captureVideoInput];
    [captureSession addOutput:captureVideoOutput];
    [captureSession commitConfiguration];
    [captureSession startRunning];
    }


// AVCaptureVideoDataOutputSampleBufferDelegate
// AVCaptureAudioDataOutputSampleBufferDelegate
//
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection 
    {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    if ( captureOutput==captureVideoOutput )
        {
        [self performImageCaptureFrom:sampleBuffer fromConnection:connection];
        }

    [pool drain];
    } 



- (void) performImageCaptureFrom:(CMSampleBufferRef)sampleBuffer
    {
    CVImageBufferRef imageBuffer;

    if ( CMSampleBufferGetNumSamples(sampleBuffer) != 1 )
        return;
    if ( !CMSampleBufferIsValid(sampleBuffer) )
        return;
    if ( !CMSampleBufferDataIsReady(sampleBuffer) )
        return;

    imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 

    if ( CVPixelBufferGetPixelFormatType(imageBuffer) != kCVPixelFormatType_32BGRA )
        return;

    CVPixelBufferLockBaseAddress(imageBuffer,0); 

    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer); 
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    int bufferSize = bytesPerRow * height;

    uint8_t *tempAddress = malloc( bufferSize );
    memcpy( tempAddress, baseAddress, bytesPerRow * height );

    baseAddress = tempAddress;

    //
    // Apply affects to the pixels stored in (uint32_t *)baseAddress
    //
    //
    // example: grayScale( (uint32_t *)baseAddress, width, height );
    // example: sepia( (uint32_t *)baseAddress, width, height );
    //

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
    CGContextRef newContext = nil;

    if ( cameraDeviceSetting != CameraDeviceSetting640x480 )        // not an iPhone4 or iTouch 5th gen
        newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace,  kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipFirst);
    else
        newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);

    CGImageRef newImage = CGBitmapContextCreateImage( newContext );
    CGColorSpaceRelease( colorSpace );
    CGContextRelease( newContext );

    free( tempAddress );

    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    if ( newImage == nil )
        {
        return;
        }

    // To be able to display the CGImageRef newImage in your UI you will need to do it like this
    // because you are running on a different thread here…
    //
    [self performSelectorOnMainThread:@selector(newCameraImageNotification:) withObject:(id)newImage waitUntilDone:YES];
    }

Answer 2

您可以在图像上叠加视图并更改混合模式以匹配黑/白效果。

查看 Apple 的 QuartzDemo，特别是演示，混合模式示例

Answer 3

另一种方法是使用 AVFoundation 转换每个帧。我对此没有太多经验，但 WWDC2010 的“第 409 期 - 使用带有 AVFoundation 的相机”视频及其示例项目应该对帮助您解决问题大有帮助。

当然，前提是您可以使用 iOS4 类。