GPUImage - How to associate filters with GPUImagePicture?

Question

GPUImage - How to associate filters with GPUImagePicture?

I want to achieve the same effect as in the “Harris Corner detection” in the GPUImage FilterShowcase, but with GPUImagePicture instead of GPUImageVideoCamera .

I cannot get the filter chain to work. Here is my current code:

 -(UIImage*)addHarrisCornerToImage:(UIImage*)inputImage { GPUImagePicture *stillImageSource = [[GPUImagePicture alloc] initWithImage:inputImage]; GPUImageHarrisCornerDetectionFilter *cornerDetectionFilter = [[GPUImageHarrisCornerDetectionFilter alloc] init]; [(GPUImageHarrisCornerDetectionFilter *)_filter setThreshold:0.20]; GPUImageCrosshairGenerator *crosshairGenerator = [[GPUImageCrosshairGenerator alloc] init]; crosshairGenerator.crosshairWidth = 15.0; [crosshairGenerator forceProcessingAtSize:CGSizeMake(480.0, 640.0)]; [(GPUImageHarrisCornerDetectionFilter *)_filter setCornersDetectedBlock:^(GLfloat* cornerArray, NSUInteger cornersDetected, CMTime frameTime) { [crosshairGenerator renderCrosshairsFromArray:cornerArray count:cornersDetected frameTime:frameTime]; }]; GPUImageAlphaBlendFilter *blendFilter = [[GPUImageAlphaBlendFilter alloc] init]; [blendFilter forceProcessingAtSize:CGSizeMake(480.0, 640.0)]; GPUImageGammaFilter *gammaFilter = [[GPUImageGammaFilter alloc] init]; [stillImageSource addTarget:gammaFilter]; [gammaFilter addTarget:blendFilter]; [crosshairGenerator addTarget:blendFilter]; GPUImagePicture *crosshairImageSource = [[GPUImagePicture alloc] initWithImage:[crosshairGenerator imageFromCurrentlyProcessedOutput]]; [crosshairImageSource addTarget:cornerDetectionFilter]; [stillImageSource addTarget:cornerDetectionFilter]; [stillImageSource processImage]; UIImage *imageWithCorners = [cornerDetectionFilter imageFromCurrentlyProcessedOutput]; return imageWithCorners; }

If I use the video feed as a source, it works fine and it looks like this:

 -(void)addHarrisCorner { _videoCamera = [[GPUImageVideoCamera alloc] initWithSessionPreset:AVCaptureSessionPreset640x480 cameraPosition:AVCaptureDevicePositionBack]; _videoCamera.outputImageOrientation = UIInterfaceOrientationPortrait; GPUImageView *filteredVideoView = [[GPUImageView alloc] initWithFrame:CGRectMake(10, 150, 300, 300)]; _filter = [[GPUImageHarrisCornerDetectionFilter alloc] init]; [(GPUImageHarrisCornerDetectionFilter *)_filter setThreshold:0.20]; GPUImageCrosshairGenerator *crosshairGenerator = [[GPUImageCrosshairGenerator alloc] init]; crosshairGenerator.crosshairWidth = 15.0; [crosshairGenerator forceProcessingAtSize:CGSizeMake(480.0, 640.0)]; [(GPUImageHarrisCornerDetectionFilter *)_filter setCornersDetectedBlock:^(GLfloat* cornerArray, NSUInteger cornersDetected, CMTime frameTime) { [crosshairGenerator renderCrosshairsFromArray:cornerArray count:cornersDetected frameTime:frameTime]; }]; GPUImageAlphaBlendFilter *blendFilter = [[GPUImageAlphaBlendFilter alloc] init]; [blendFilter forceProcessingAtSize:CGSizeMake(480.0, 640.0)]; GPUImageGammaFilter *gammaFilter = [[GPUImageGammaFilter alloc] init]; [_videoCamera addTarget:gammaFilter]; [gammaFilter addTarget:blendFilter]; [crosshairGenerator addTarget:blendFilter]; [blendFilter addTarget:filteredVideoView]; [_videoCamera addTarget:_filter]; [_filter addTarget:filteredVideoView]; [_videoCamera startCameraCapture]; [[self view] addSubview:filteredVideoView]; }

I am really not sure about GPUImagePicture *crosshairImageSource = [[GPUImagePicture alloc] initWithImage:[crosshairGenerator imageFromCurrentlyProcessedOutput]]; and / or if I have to use [stillImageSource processImage]; after each added filter.

Can someone point me in the right direction?

thanks

* UPDATE *

Having looked at FeatureExtractionTest in the GPUImage folder, I managed to do some work, but it did not find any angles. Output signal Number of corners: 0 . I played with threshold , sensitivity and blurSize .

Here's the new code:

 - (void)testCornerDetectorWithPicture:(UIImage *)image { // GPUImagePicture *pictureInput = [[GPUImagePicture alloc] initWithImage:image]; GPUImagePicture *pictureInput = [[GPUImagePicture alloc] initWithImage:[UIImage imageNamed:@"testCorner.png"]]; _harrisCornerFilter = [[GPUImageHarrisCornerDetectionFilter alloc] init]; _harrisCornerFilter.threshold = 0.2; _harrisCornerFilter.sensitivity = 5.0; _harrisCornerFilter.blurSize = 1.0; [pictureInput removeAllTargets]; [pictureInput addTarget:_harrisCornerFilter]; __weak typeof(self) weakSelf = self; [_harrisCornerFilter setCornersDetectedBlock:^(GLfloat* cornerArray, NSUInteger cornersDetected, CMTime frameTime) { GPUImageCrosshairGenerator *crosshairGenerator = [[GPUImageCrosshairGenerator alloc] init]; crosshairGenerator.crosshairWidth = 10.0; [crosshairGenerator setCrosshairColorRed:1.0 green:0.0 blue:0.0]; [crosshairGenerator forceProcessingAtSize:[pictureInput outputImageSize]]; GPUImageAlphaBlendFilter *blendFilter = [[GPUImageAlphaBlendFilter alloc] init]; [blendFilter forceProcessingAtSize:[pictureInput outputImageSize]]; [pictureInput addTarget:blendFilter]; [crosshairGenerator addTarget:blendFilter]; [blendFilter prepareForImageCapture]; NSLog(@"Number of corners: %d", cornersDetected); [crosshairGenerator renderCrosshairsFromArray:cornerArray count:cornersDetected frameTime:frameTime]; dispatch_async(dispatch_get_main_queue(), ^{ UIImage *crosshairResult = [blendFilter imageFromCurrentlyProcessedOutput]; [weakSelf useImageWithCornersWithImage:crosshairResult]; }); }]; [pictureInput processImage]; }