imageFromCurrentFramebufferWithOrientation returns nil GPUImagePicture?

Question

I want to convert image to black and white. i have tried the following code but imageFromCurrentFramebufferWithOrientation always returns nil.

-(UIImage *)convertImageToBlackAndWhite:(UIImage *)image{
GPUImagePicture *gpuImage = [[GPUImagePicture alloc] initWithImage:image];
GPUImageSobelEdgeDetectionFilter *edgeFilter = [[GPUImageSobelEdgeDetectionFilter alloc] init];

GPUImageColorMatrixFilter *conversionFilter = [[GPUImageColorMatrixFilter alloc] init];
conversionFilter.colorMatrix = (GPUMatrix4x4){
    {0.0, 0.0, 0.0, 1.0},
    {0.0, 0.0, 0.0, 1.0},
    {0.0, 0.0, 0.0, 1.0},
    {1.0,0.0,0.0,0.0},
};

[gpuImage addTarget:edgeFilter];
[edgeFilter addTarget:conversionFilter];
[gpuImage processImage];
NSLog(@"%@",[conversionFilter imageFromCurrentFramebufferWithOrientation:0]);
return [conversionFilter imageFromCurrentFramebufferWithOrientation:0];

}

Answer 1

Per the recent changes in the way that GPUImage handles framebuffers, you need to add the line

[conversionFilter useNextFrameForImageCapture];

right before

[gpuImage processImage];

in the above code. You need to let the framework know to not recycle the framebuffer for your last filter until you've processed your image and captured the result from it.