GPUImage滤镜组出现问题

Question

I am trying to apply some filter to an image , so I use GPUImageFilterGroup to blend filters , but my app crashes , here is my code :

- (IBAction)effectApply:(id)sender {

    GPUImageFilterGroup *groupFilter = [[GPUImageFilterGroup alloc]init];
     GPUImagePicture *stillImage= [[GPUImagePicture alloc]initWithImage:_img.image];

    GPUImageBrightnessFilter *brightnessFilter = [[GPUImageBrightnessFilter alloc]init];
    [brightnessFilter setBrightness:.4];

    GPUImageContrastFilter *contrastFilter = [[GPUImageContrastFilter alloc]init];
    [contrastFilter setContrast:2.0];

    GPUImageExposureFilter *exposureFilter =[[GPUImageExposureFilter alloc]init];
    [exposureFilter setExposure:.2];


    [groupFilter addFilter:brightnessFilter];
    [groupFilter addFilter:contrastFilter];
    [groupFilter addFilter:exposureFilter];


    [(GPUImageFilterGroup *) groupFilter setInitialFilters:[NSArray arrayWithObject: brightnessFilter]];
    [(GPUImageFilterGroup *) groupFilter setTerminalFilter:exposureFilter];


    [stillImage addTarget:filter];

    [filter useNextFrameForImageCapture];
    [stillImage processImage];

    UIImage *currentFilteredVideoFrame = [filter imageFromCurrentFramebuffer];

    _img.image = currentFilteredVideoFrame;

}

Crash logs :

2014-07-10 15:27:03.955 Effect Test[65595:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
*** First throw call stack:
(
    0   CoreFoundation                      0x00000001021b9495 __exceptionPreprocess + 165
    1   libobjc.A.dylib                     0x0000000101f1899e objc_exception_throw + 43
    2   CoreFoundation                      0x0000000102170374 -[__NSArrayM insertObject:atIndex:] + 820
    3   Effect Test                         0x0000000100012077 __46-[GPUImageOutput addTarget:atTextureLocation:]_block_invoke + 103
    4   libdispatch.dylib                   0x000000010370e72d _dispatch_client_callout + 8
    5   libdispatch.dylib                   0x00000001036fd5d0 _dispatch_barrier_sync_f_invoke + 57
    6   Effect Test                         0x000000010001147c runSynchronouslyOnVideoProcessingQueue + 108
    7   Effect Test                         0x0000000100011fb0 -[GPUImageOutput addTarget:atTextureLocation:] + 272
    8   Effect Test                         0x000000010001637c -[GPUImagePicture addTarget:atTextureLocation:] + 108
    9   Effect Test                         0x0000000100011e56 -[GPUImageOutput addTarget:] + 86
    10  Effect Test                         0x000000010000167b -[ViewController effectApply:] + 667
    11  UIKit                               0x0000000100ac6f06 -[UIApplication sendAction:to:from:forEvent:] + 80
    12  UIKit                               0x0000000100ac6eb4 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 17
    13  UIKit                               0x0000000100ba3880 -[UIControl _sendActionsForEvents:withEvent:] + 203
    14  UIKit                               0x0000000100ba2dc0 -[UIControl touchesEnded:withEvent:] + 530
    15  UIKit                               0x0000000100afdd05 -[UIWindow _sendTouchesForEvent:] + 701
    16  UIKit                               0x0000000100afe6e4 -[UIWindow sendEvent:] + 925
    17  UIKit                               0x0000000100ad629a -[UIApplication sendEvent:] + 211
    18  UIKit                               0x0000000100ac3aed _UIApplicationHandleEventQueue + 9579
    19  CoreFoundation                      0x0000000102148d21 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
    20  CoreFoundation                      0x00000001021485f2 __CFRunLoopDoSources0 + 242
    21  CoreFoundation                      0x000000010216446f __CFRunLoopRun + 767
    22  CoreFoundation                      0x0000000102163d83 CFRunLoopRunSpecific + 467
    23  GraphicsServices                    0x0000000104f93f04 GSEventRunModal + 161
    24  UIKit                               0x0000000100ac5e33 UIApplicationMain + 1010
    25  Effect Test                         0x0000000100001bc3 main + 115
    26  libdyld.dylib                       0x000000010395f5fd start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

 GPUImageFilterGroup *groupFilter = [[GPUImageFilterGroup alloc]init];

   [groupFilter addTarget:brightnessFilter];
   [brightnessFilter addTarget: contrastFilter];
   [contrastFilter addTarget: exposureFilter];

  [(GPUImageFilterGroup *) groupFilter setInitialFilters:[NSArray arrayWithObject: brightnessFilter]];
  [(GPUImageFilterGroup *) groupFilter setTerminalFilter:exposureFilter]; 

[stillImage addTarget:groupFilter];

Hope it helps