GPUImage更改img色温

Question

我有一个UIImage读取表单相册，并且使用GPUImage做一些事情，例如：

GPUImagePicture* picture = [[GPUImagePicture alloc] initWithImage:srcImage]; // srcImage is an UIImage
GPUImageFilter *resultFilter = [[GPUImageFilter alloc] init];
[picture addTarget:resultFilter];
[resultFilter useNextFrameForImageCapture];
[picture processImage];
UIImage* resultImg = [resultFilter imageFromCurrentFramebuffer];

或

GPUImageFilter *resultFilter = [[GPUImageFilter alloc] init];
[resultFilter useNextFrameForImageCapture];
resultImg = [resultFilter imageByFilteringImage:srcImage];

我期望srcImage完全等于resultImg，因为GPUImagePicture和GPUImageFilter什么都不做，但是结果是resultImg的色温比srcImage冷