GPUImageColorBalanceFilter无效

Question

我正在使用https://github.com/liovch/GPUImage中定义的GPUImageColorBalanceFilter。但过滤后的图像在显示时根本没有从原始图像改变！代码运行良好，没有错误。我做错了什么？

CGImageRef cgimg = [context createCGImage:beginImage
                                 fromRect:[beginImage extent]];
BOOL preserveLuminosity = NO;
GPUVector3 shadows= (GPUVector3){1,0.0,1};
GPUVector3 midtones = (GPUVector3){-1,-1,0.13};
GPUVector3 highlights = (GPUVector3){0.0,-1,1};
UIImage *img1 = [UIImage imageWithCGImage:cgimg];
GPUImagePicture *pic1 = [[GPUImagePicture alloc] initWithImage:img1];
GPUImageColorBalanceFilter *filter1 = [[GPUImageColorBalanceFilter alloc] init];
[filter1 setShadows:shadows];
[filter1 setMidtones:midtones];
[filter1 setHighlights:highlights];
[filter1 setPreserveLuminosity:preserveLuminosity];
[pic1 addTarget:filter1];
[pic1 processImage];

UIImage *new= filter1.imageFromCurrentlyProcessedOutput;
self.imageView.image = new;
CGImageRelease(cgimg);

注意：由于我已经在使用bradlarson的GPUImage库，因此我将https://github.com/liovch/GPUImage中的GPUImageColorBalanceFilter.h，GPUImageColorBalanceFilter.m，GPUImageOpenGLESContext.h，GPUImageOpenGLESContext.m添加到我的代码库中。