The document discusses Core Image, an Apple framework for image processing that allows near real-time effects for still and video images. It covers core concepts, workflows involving CIImage and CIFilter, various filter categories, and practical demos for applying filters and rendering images. Additionally, it includes advanced usage such as chaining filters and utilizing Core Image in applications using video and custom effects.

1. Core Image
The Most Fun API
You’re Not Using
Chris Adamson • @invalidname
CocoaConf Columbus, August 2014

4. “Core Image is an image processing and analysis
technology designed to provide near real-time
processing for still and video images.”

5. Agenda
• Images, Filters, and Contexts
• The Core Image Filter Gallery
• Neat Tricks with Built-In Filters
• Core Image on OS X

6. Core Image, Core Concepts
• Core Image is
of the time
• A chain of filters describes a “recipe” of processing
steps to be applied to one or more images
• “Stringly typed”
• You only get pixels when you render

7. Typical Workflow
• Start with a source CIImage
• Apply one or more filters
• Render resulting CIImage to a CIContext, or
convert CIImage out to another type
• A few filters take or produce types other than
CIImage (CIQRCodeGenerator)

8. CIImage
• An image provided to or produced by Core Image
• But no bitmap of pixel data!
• Immutable
• -imageByCroppingToRect,
-imageByApplyingTransform
• -extent — a CGRect of the image’s size

9. CIImage sources
• NSURL
• CGImageRef
• Bitmap or JPEG/PNG/TIFF in NSData
• OpenGL texture
• Core Video image/pixel buffer

10. CIContext
• Rendering destination for a CIImage (-
[drawImage:inRect:fromRect:])
• This is where you get pixels (also, this is the processor-
intenstive part)
• On iOS, must be created from an EAGLContext. On
Mac, can be created with CGContextRef
• Can also produce output as a CGImageRef, bitmap data,
or a CVPixelBuffer (iOS only)

11. ????

12. CIFilter
• Performs an image processing operation
• Typically takes and produces a CIImage
• All parameters are provided via -[setValue:forKey:]
• Stringly-typed!
• Output is retrieved with -[valueForKey:]

13. –Core Image Cat
“I can has filterz?

14. Yes, you can has Filterz!

16. Core Image Filter Reference
Filter Name
Parameters
Note the type & number to
provide
Categories
Watch for CICategoryBuiltIn
and CICategoryVideo
Example Figure
Availability
Watch for versioning and
OS X-only filters

17. Filter Categories
• Group filters by functionality: CICategoryBlur,
CICategoryGenerator,
CICategoryCompositeOperation, etc.
• Also group filters by availability and
appropriateness: CICategoryBuiltIn,
CICategoryVideo, CICategoryNonSquarePixels

18. CICategoryGenerator
• No input image, just produces an output
• CICategoryGradient is also output-only
• Example: CICheckerboardGenerator

19. CICategoryBlur
• Algorithmically spreads/blends pixels
• CICategorySharpen offers an opposite effect
• Example: CIGaussianBlur

20. CICategoryColorAdjustement
• Changes distribution of color throughout an image
• Example: CIColorControls (adjusts saturation,
brightness, contrast)

21. CICategoryColorEffect
• Color changes that affect the subjective nature of
the image
• Example: CIPhotoEffectNoir

22. CICategoryDistortionEffect
• Moves pixels to achieve an effect
• Example: CITorusLensDistortion

23. CICategoryStylize
• Various stylistic effects
• Example: CIPointillize

24. CICategoryGeometryAdjustment
• Moves pixels via cropping, affine transforms, etc.
• Example: CICrop

25. CICategoryTileEffect
• Repeatedly copies all or part of an image
• Example: CIAffineTile

26. CICategoryCompositeOperation
• Combines multiple images
• Example: CISourceOverCompositing

27. Demo

28. Creating CIColorControls Filter
_colorControlsFilter

29. Setting input values
[self
! ! ! ! ! ! ! ! ! ! ! !
[self
! ! ! ! ! ! ! ! ! ! ! !
[self
! ! ! ! ! ! ! ! ! ! ! !

30. Setting input image
CIImage
! ! ! ! ! ! ! ! ! !
[self
! ! ! ! ! ! ! !

31. Getting output image
ciImage = [
UIImage
self

32. Other output options
• Use a CIContext
• -[drawImage:inRect:fromRect:] draws pixels to
the EAGLContext (iOS) or CGContextRef (OS
X) that the CIContext was created from.
• CIContext can also render to a void* bitmap
• On iOS, can create a CVPixelBufferRef, typically
used for writing to a file with AVAssetWriter

33. Chaining filters
• Use the output of one filter as the input to the next
• This doesn’t cost anything, because the CIImages
just hold state, not pixels

34. Demo

35. Creating CIContext
if (!
! !
! ! ! ! ! !
! !
}!
! ! !
// make CIContext from GL context, clearing out default color space
self
! ! ! ! ! ! ! ! ! ! ! ! !
! ! ! !
! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !
!
Note: This is in a subclass of GLKView

36. Set up Sepia Tone filter
_sepiaToneFilter
[_sepiaToneFilter
! ! ! ! ! ! ! ! !

37. Set up Mask to Alpha filter
UIImage
_circleMaskFilter
CIImage
! ! ! ! ! ! ! ! ! ! ! ! circleImageUI.
[_circleMaskFilter
! ! ! ! ! ! !
_circleMask
circle-mask-100x100.png

38. Set up Blend with Mask filter
_constantColorGeneratorFilter
! ! ! ! ! ! ! ! ! !
[_constantColorGeneratorFilter
! ! ! [
! ! ! ! ! ! ! ! ! ! ! ! ! !
forKey
_backgroundAlphaFill
! ! ! ! ! ! ! ! ! ! !
!
_blendWithMaskFilter
[_blendWithMaskFilter
! ! ! ! ! ! ! !
[_blendWithMaskFilter
! ! ! ! ! ! ! !

39. Apply filters
// Get CIImage from source image
CGImageRef
! ! ! ! ! ! ! !
loupeImage = [
!
// Apply sepia filter
[self
loupeImage = [
!
// Set sepia-filtered image as input to blend-with-mask
[_blendWithMaskFilter
! ! ! ! ! !
loupeImage = [

40. Render in CIContext
if ([
! [
}!
! !
[self
!
// GL-on-Retina fix
CGRect
drawBoundsInPoints.
drawBoundsInPoints.
! !
// drawing to CIContext draws to the EAGLESContext it's based on
[self
! ! ! ! !! ! !
! ! ! ! ! ! ! !
!
// Refresh GLKView contents immediately
[self

41. Working with Video
• AVFoundation AVCaptureVideoDataOutput and
AVAssetReader deliver CMSampleBuffers
• CMSampleBuffers have timing information and
CVImageBuffers/CVPixelBuffers
• +[CIImage imageWithCVPixelBuffer:]

42. Demo

43. Chroma Key (“green screen”
recipe
• Use a CIColorCube to map green-ish colors to
transparent
• Use CISourceOverCompositing to draw this
alpha’ed image over another image

44. CIColorCube
Maps colors from one RGB “cube” to another
http://en.wikipedia.org/wiki/RGB_color_space

45. Using CIColorCube
CIColorCube maps green(-ish) colors to 0.0 alpha, all
other colors pass through

46. CISourceOverCompositing
inputBackgroundImage inputImage
outputImage

47. CIColorCube Dataconst unsigned int size = 64;!
size_t cubeDataSize = size * size * size * sizeof (float) * 4;!
float *keyCubeData = (float *)malloc (cubeDataSize);!
//! float *alphaMatteCubeData = (float *)malloc (cubeDataSize);!
//! float rgb[3], hsv[3], *keyC = keyCubeData, *alphaC = alphaMatteCubeData;!
float rgb[3], hsv[3], *keyC = keyCubeData;!
// Populate cube with a simple gradient going from 0 to 1!
for (int z = 0; z < size; z++){!
! rgb[2] = ((double)z)/(size-1); // Blue value!
! for (int y = 0; y < size; y++){!
! ! rgb[1] = ((double)y)/(size-1); // Green value!
! ! for (int x = 0; x < size; x ++){!
! ! ! rgb[0] = ((double)x)/(size-1); // Red value!
!
! ! ! // Convert RGB to HSV!
! ! ! // You can find publicly available rgbToHSV functions on the Internet!
!
! ! ! RGBtoHSV(rgb[0], rgb[1], rgb[2],!
! ! ! ! ! &hsv[0], &hsv[1], &hsv[2]);!
!
! ! ! // RGBtoHSV uses 0 to 360 for hue, while UIColor (used above) uses 0 to 1.!
! ! ! hsv[0] /= 360.0;!
! ! ! !
! ! ! // Use the hue value to determine which to make transparent!
! ! ! // The minimum and maximum hue angle depends on!
! ! ! // the color you want to remove!
! ! ! !
! ! ! bool keyed = (hsv[0] > minHueAngle && hsv[0] < maxHueAngle) &&!
! ! ! (hsv[1] > minSaturation && hsv[1] < maxSaturation) &&!
! ! ! (hsv[2] > minBrightness && hsv[2] < maxBrightness);!
! ! ! !
! ! ! float alpha = keyed ? 0.0f : 1.0f;!
! ! ! !
! ! ! // re-calculate c pointer!
! ! ! keyC = (((z * size * size) + (y * size) + x) * sizeof(float)) + keyCubeData;!
! ! ! !
! ! ! // Calculate premultiplied alpha values for the cube!
! ! ! keyC[0] = rgb[0] * alpha;!
! ! ! keyC[1] = rgb[1] * alpha;!
! ! ! keyC[2] = rgb[2] * alpha;!
! ! ! keyC[3] = alpha;!
! ! ! ! ! ! ! !
! ! }!
! }!
}!
See “Chroma Key Filter Recipe” in Core Image Programming Guide

48. Create CIColorCube from
mapping data
// build the color cube filter and set its data to above!
self.colorCubeFilter = [CIFilter filterWithName:@"CIColorCube"];!
[self.colorCubeFilter setValue:[NSNumber numberWithInt:size]!
! !! ! ! ! ! ! ! ! forKey:@"inputCubeDimension"];!
NSData *data = [NSData dataWithBytesNoCopy:keyCubeData!
! !! ! ! ! ! ! ! length:cubeDataSize!
! !! ! ! ! ! freeWhenDone:YES];!
[self.colorCubeFilter setValue:data forKey:@"inputCubeData"];!

49. Create CISourceOverCompositing
// source over filter!
self.backgroundImage = [UIImage imageNamed:!
! !! ! ! ! ! ! ! ! ! @"img_washington_small_02.jpg"]; !
self.backgroundCIImage = [CIImage imageWithCGImage:!
! !! ! ! ! ! ! ! ! ! ! self.backgroundImage.CGImage];!
self.sourceOverFilter = [CIFilter filterWithName:!
! !! ! ! ! ! ! ! ! ! @"CISourceOverCompositing"];!
[self.sourceOverFilter setValue:self.backgroundCIImage !
! !! ! ! ! ! ! ! forKeyPath:@"inputBackgroundImage"];!

50. Apply Filters in Capture Callback
CIImage *bufferCIImage = [CIImage imageWithCVPixelBuffer:cvBuffer];!
!
[self.colorCubeFilter setValue:bufferCIImage !
! !! ! ! ! ! ! ! ! ! forKey:kCIInputImageKey];!
CIImage *keyedCameraImage = [self.colorCubeFilter valueForKey:!
! !! ! ! ! ! ! ! ! ! ! ! kCIOutputImageKey];!
!
[self.sourceOverFilter setValue:keyedCameraImage !
! !! ! ! ! ! ! ! ! forKeyPath:kCIInputImageKey];!
!
CIImage *compositedImage = [self.sourceOverFilter valueForKeyPath:!
! !! ! ! ! ! ! ! ! ! ! kCIOutputImageKey];
Then draw compositedImage to CIContext as before

51. Other Points of Interest
• CIQRCodeGenerator filter — Converts data (e.g., a string) to
a QR Code
• CILenticularHaloGenerator filter — aka, lens flare
• CIDetector — Class (not a filter) to find features in images.
Currently only supports face finding (returned as an array of
CIFeatures). Optionally detects smiles and eye blinks within
faces.
• CIImage has a red-eye enhancement that takes the array of
face CIFeatures to tell it where to apply the effect

52. Core Image on OS X
• Core Image is part of QuartzCore (or Image Kit), so
you don’t @import CoreImage
• Many more filters are available
• Can create your own filter with OpenGL Shading
Language (plus some CI extensions). See CIKernel.
• Also available in iOS 8
• Filters can be set on CALayers

53. CALayer Filters on OS X
• Views must be layer-backed (obviously)
• Must also call -[NSView
setLayerUsesCoreImageFilters:] on 10.9+
• CALayer has properties: filters, compositingFilter,
backgroundFilters, minificationFilter,
magnificationFilter
• These exist on iOS, but do nothing

54. Demo

55. Adding CIPixellate to layer’s
filters
self
! !! ! ! ! ! ! ! !
self
[self
! !! ! ! ! ! [
! !! ! ! ! ! ! ! !
!
[self
! !! ! !
! !! ! ! ! ! ! ! ! !
self
! !! ! !

56. Updating a layer’s filters
-(void
! [
! !! ! ! !
! !! ! ! ! ! ! ! ! ! !
! !! ! ! !
}

57. Wrap Up: Stuff to Remember
• Get psyched about filters, but remember to check
that they’re on your targeted platform/version.
• Drawing to a CIContext on iOS must be GL-
backed (e.g., with a GLKView)

58. Q&A
Slides and code will be posted to:
http://www.slideshare.net/invalidname/
!
@invalidname
http://subfurther.com/blog