GPUImage change brightness with UISlider - iphone

Question

How can i change the brightness of an Image with slider using GPUImageBrightnessFilter ?
I tried,
-(void)updateBrightness {
GPUImageFilter *selectedFilter = nil;
[selectedFilter removeAllTargets];
selectedFilter = [[GPUImageFilter alloc] init];
CGFloat midpoint = [(UISlider *)sender value];
[(GPUImageBrightnessFilter *)settingsFilter setBrightness:midpoint];
UIImage *filteredImage = [selectedFilter imageByFilteringImage:_image_view.image];
fx_imageView.image = filteredImage;
}

Answer 1

There are several problems with the above code.
First, you're not actually using a brightness filter against your image, because you're calling -imageByFilteringImage: on selectedFilter, which is a generic GPUImageFilter that you allocated fresh. Your GPUImageBrightnessFilter of settingsFilter is never used.
Second, you don't want to be allocating a new filter with every time you update a parameter. Allocate your GPUImageBrightnessFilter once and simply update it as values change.
Third, you don't want to keep re-filtering UIImages. Going to and from UIImages is a slow process (and won't work properly when using -imageByFilteringImage: on the same filter, because of some caching I do). Instead, create a GPUImagePicture based on your original image, add a GPUImageBrightnessFilter to that as a target, and target your GPUImageBrightnessFilter at a GPUImageView. Use -processImage every time you update your brightness filter and your updates will be much, much faster. When you need to extract your final image, use -imageFromCurrentlyProcessedOutput.

Answer 2

these may help you...
-(void)viewDidLoad
{
[sliderChange setMinimumValue:-0.5];
[sliderChange setMaximumValue:0.5];
[sliderChange setValue:0.0];
brightnessFilter = [[GPUImageBrightnessFilter alloc] init];
}
-(IBAction)upDateSliderValue:(id)sender
{
GPUImagePicture *fx_image;
fx_image = [[GPUImagePicture alloc] initWithImage:originalImage];
[brightnessFilter setBrightness:self.sliderChange.value];
[fx_image addTarget:brightnessFilter];
[fx_image processImage];
UIImage *final_image = [brightnessFilter imageFromCurrentlyProcessedOutput];
self.selectedImageView.image = final_image;
}