iOS 图片处理问题

Question

比如对图片进行实时亮度调整

用GPUImage处理如下

    self.brightnessFilter = [[GPUImageBrightnessFilter alloc] init];
    self.imagePicture = [[GPUImagePicture alloc] initWithImage:_originImage];
    [self.imagePicture addTarget:_brightnessFilter];
    [self.imagePicture processImage];

- (IBAction)valueChangeAction:(UISlider *)brightnessSlider{
  [self.brightnessFilter setBrightness:[brightnessSlider value]];
  self.editImageView.image = [self.brightnessFilter imageByFilteringImage:_originImage];
        
}

1. [self.brightnessFilter imageByFilteringImage:_originImage];这个获取处理后图片的方法是否正确，看到stackoverflow上的回答都是[self.brightnessFilter imageFromCurrentlyProcessedOutput]这样来获取的，但这个方法貌似已经弃用了，哪种方法才是正确的，还是我前面的代码也有问题？

2. iPhone 5s真机调试发现实时的调整会存在卡顿的现象，但原始图片质量并不是很高，尝试过异步的方案，仍然会出现卡顿，具体要如何处理才能避免这种情况？

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [self.brightnessFilter setBrightness:[brightnessSlider value]];
        dispatch_async(dispatch_get_main_queue(), ^{
            self.editImageView.image = [self.brightnessFilter imageByFilteringImage:_originImage];
        });
    });

Answer 1

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [self.brightnessFilter setBrightness:[brightnessSlider value]];
        dispatch_async(dispatch_get_main_queue(), ^{
            self.editImageView.image = [self.brightnessFilter imageByFilteringImage:_originImage];
        });
    });

[self.brightnessFilter imageByFilteringImage:_originImage]这句可能也会阻塞主线程。

改成下面这样试试呢

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [self.brightnessFilter setBrightness:[brightnessSlider value]];
        UIImage *image = [self.brightnessFilter imageByFilteringImage:_originImage];
        dispatch_async(dispatch_get_main_queue(), ^{
            self.editImageView.image = image;
        });
    });

Answer 2

你竟然用valueChangeAction:这个方法，你拖动slider的时候，这个方法会被不断被调用，然后不断的处理图片，不卡才奇怪，你应该使用UIControlEventTouchUpInside这个时间，拖动结束的时候才处理图片。如果你非要使用UIControlEventValueChanged，那在valueChangeAction做一下处理。