Share your Image Proccessing (filter) code

[arubinst]

Hello everyone, I'll start by saying that this thread is awesome! Very, very useful.

I'm sorry to bring it back to life, but I have a problem that maybe some of you might help me solve.

I'm thresholding an image by using some code obtained from the examples shown here. I started by using a fixed threshold value and then moved to a slider. Both cases worked as expected. The slider gives a very nice effect as the changes reflect immediately when the slider is moved, because the image is very small.

I'm now trying to implement a kind of "automatic" thresholding inside a loop. What I would like to do is apply the thresholding routine for a varying threshold value and be able to reflect the changes on the image as the threshold value changes.

The problem is that you cannot see any progress. Changes are only updated after the loop finishes executing.

I have tried setNeedsDisplay on the UIImageView and on the parent view. I'm also delaying the loop with a [NSThread sleepForTimeInterval:xx] but the result is always the same. I cannot see the image changing. I only obtain the final version after the loop.

Any ideas?

Thanks!

[shizam]

Thank you all,
This thread has been immensely helpful and I have several matrix transforms working but I have one big problem:

On a 5MP image on an iPhone4G they take upwards of 10-11 seconds to process the full image (by iterating over each pixel as illustrated in this thread). Anybody have a way to speed this up, is it better to do work on PNG vs JPG data, is there a way to hardware accelerate it?

Thanks

[RednebMas]

I know that this is a really old thread but I have been looking at it a lot and if anyone else out there is I would like to help. It also fixes the problems that I have been having with the previous code. For example, in the previous code on this topic, if you made no changes to the image it would have a different output.

There is a much easier way to edit each pixel individually. Here is a function that returns the image without red. Code is from here Can I edit the pixels of the UIImage's property CGImage - Stack Overflow

- (UIImage *)imageProcess:(UIImage *)image
{
    // load image
    CGImageRef imageRef = image.CGImage;
    NSData *data        = (NSData *) CGDataProviderCopyData(CGImageGetDataProvider(imageRef));
    char *pixels        = (char *)[data bytes];
	
    // manipulate the individual pixels
    for(int i = 0; i < [data length]; i += 4)
    {
        int r = i;
        int g = i+1;
        int b = i+2;
        int a = i+3;
		
        pixels[r]   = 0;
        pixels[g]   = pixels[g];
        pixels[b]   = pixels[b];
        pixels[a]   = pixels[a];
    }
	
    // create a new image from the modified pixel data
    size_t width                    = CGImageGetWidth(imageRef);
    size_t height                   = CGImageGetHeight(imageRef);
    size_t bitsPerComponent         = CGImageGetBitsPerComponent(imageRef);
    size_t bitsPerPixel             = CGImageGetBitsPerPixel(imageRef);
    size_t bytesPerRow              = CGImageGetBytesPerRow(imageRef);
	
    CGColorSpaceRef colorspace      = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo         = CGImageGetBitmapInfo(imageRef);
    CGDataProviderRef provider      = CGDataProviderCreateWithData(NULL, pixels, [data length], NULL);
	
    CGImageRef newImageRef = CGImageCreate (
											width,
											height,
											bitsPerComponent,
											bitsPerPixel,
											bytesPerRow,
											colorspace,
											bitmapInfo,
											provider,
											NULL,
											false,
											kCGRenderingIntentDefault
											);
    // the modified image
    UIImage *newImage   = [UIImage imageWithCGImage:newImageRef];
	
    // cleanup
    free(pixels);
    CGImageRelease(imageRef);
    CGColorSpaceRelease(colorspace);
    CGDataProviderRelease(provider);
    CGImageRelease(newImageRef);
	
	return newImage;
}

[rocotilos]

Originally Posted by shizam

Thank you all,
This thread has been immensely helpful and I have several matrix transforms working but I have one big problem:

On a 5MP image on an iPhone4G they take upwards of 10-11 seconds to process the full image (by iterating over each pixel as illustrated in this thread). Anybody have a way to speed this up, is it better to do work on PNG vs JPG data, is there a way to hardware accelerate it?

Thanks

As far as I know, there is no way to speed it up. Speed pretty much depends on CPU speed of the hardware. If you want, you can try using image editing with openGL, but i doubt it will improve speed.. because if you have big chunk of pizza, no matter how u split the chunk, if you have 10 people eating it, the total time to be completely eaten is going to be same.

[mkotliarov]

Hello arubinst, I'm trying to do an image binarization app. I've read a lot of documents from Internet about image binarization, thresholding and so on. Can you share some code to get the idea of a good thresholding algorithm? I need to do a binarization of image with text, but not doing OCR. Thanx a lot.

[Sakura]

Seems like a helpful thread about editing image data.

[JavaWizKid]

Very useful hread. How do I set the

m_PixelBuf[index + 1] = 255 - m_PixelBuf[index + 1]; 
		m_PixelBuf[index + 2] = 255 - m_PixelBuf[index + 2]; 
		m_PixelBuf[index + 3] = 255 - m_PixelBuf[index + 3];

To display the image as it is originally intended?

[Rifts]

can someone please upload an example app with source code?

[ajin2605]

Hi all,
Thanks for useful topic!
I'd like to know that did anybody here change brightness and contrast of DICOM images with touch moves event?!

If YES, would you please post the code here ?!

Thanks and regards,
DKien

[Duncan C]

This whole topic was turned upside down with the release of iOS 5. Apple finally added Core image filters in iOS 5.

Core Image (CI) filters use OpenGL shader code under the covers to do transformations on images EXTREMELY fast. Many of the filters are fast enough to operate on a video from the camera and display onto the screen in real time.

I haven't tackled using CI filters on video yet, but it's fairly straightforward to use a filter on a still image.

One gotcha is that CI filters take an object called a CIImage as input, and return a CIImage as output.

There's a UIImage method in iOS 5, initWithCIImage, that's supposed to take a CIImage as input and create a UIImage. It doesn't work. it returns a UIImage that has the correct bounds, but lacks the backing CGImage containing the pixels. I wasted a bunch of time yesterday tracking down this bug, and have submitted a radar bug. Please, everybody reading this, go write your own variation on this bug. Apple uses the number of bug reports they get to set their priorities on bug fixes.

Below is a sample method I wrote yesterday that takes a UIImage as input, and returns an adjusted UIImage as output. It uses the CIColorControls method to adjust the brightness of an image. It would be trivial to change it to use lots of different Core Image filters.

The "if (TRUE)" bit enables the work-around code that makes it possible to convert a CIIImage to a CGImage, and then to a UIImage. If you change "if (TRUE)" to "if (FALSE)", the code tries to use the Apple iOS 5 method, which doesn't work.

I got the work-around from Erica Sadun's new "iOS 5 Developer's Cookbook" from Addison Wesley. (http://www.amazon.com/iOS-Developers...6983449&sr=8-1)

This book is truly outstanding. It is chock-full of useful information, and includes a decent introduction to Objective C, Xcode, the portal, etc. Where it really shines is tons of working examples of techniques you can use to solve real-world problems in your applications.

Erica is has a PHD in computer science, and her knowledge of iOS is both deep and wide. Plus, she writes well.

I think it's the best fit for intermediate to advanced programmers. If you've got experience with development on another platform, and are learning iOS, it should be perfect.

I can't say enough good things about this book.

Unfortunately, there was a problem with the first printing, and it had to be scrapped. The new version is due out in 10 days. I have one of the misprints, and even with the printing problems, I would gladly pay twice the price for it.

- (UIImage *) changeImageBrightness: (UIImage *) anImage
                             amount: (CGFloat) amount;
{
  UIImage *adjustedUIImage;
  CIImage *adjustedCIImage;
  CGImageRef adjustedCGImage;
  CGImageRef inputCGImage = anImage.CGImage;
  CIImage *inputCIImage = [CIImage imageWithCGImage: inputCGImage];
  
  CIFilter *colorFilter = [CIFilter filterWithName: @"CIColorControls"
                                     keysAndValues: 
                           @"inputBrightness",  [NSNumber numberWithFloat: amount],
                           @"inputImage",       inputCIImage,
                           nil];
  adjustedCIImage = [colorFilter valueForKey: kCIOutputImageKey];
  
  if (TRUE)
  {
    //This works
    adjustedCGImage = [[CIContext contextWithOptions:nil] createCGImage: adjustedCIImage fromRect:inputCIImage.extent];
    adjustedUIImage = [UIImage imageWithCGImage: adjustedCGImage];
  }
  else
  {
    //This doesn't work
    adjustedUIImage = [UIImage imageWithCIImage: adjustedCIImage];
    adjustedCGImage = adjustedUIImage.CGImage;
  }
  return adjustedUIImage; 
}