Core Image

• CIFilter is a mutable object that represents an effect. A filter object has at least one input parameter and produces an output image.

• CIImage is an immutable object that represents an image. You can synthesize image data or provide it from a file or the output of another CIFilter object.

• CIContext is an object through which Core Image draws the results produced by a filter. A Core Image context can be based on the CPU or the GPU.

The basics of applying a filter to an image

CIContext *context = [CIContext contextWithOptions:nil]; // 1

CIImage *image = [CIImage imageWithContentsOfURL:myURL]; // 2

CIFilter *filter = [CIFilter filterWithName:@"CISepiaTone"]; // 3

[filter setValue:image forKey:kCIInputImgeKey];

[filter setValue:[NSNumber numberWithFloat:0.8f] forKey:@"InputIntensity"];

CIImage *result = [filter valueForKey:kCIOutputImageKey]; // 4

CGImageRef cgImage = [context createCGImage:result fromRect:[result extent];

A filter category specifies the type of effect—blur, distortion, generator, and so forth—or its intended use—still images, video, nonsquare pixels, and so on. A filter can be a member of more than one category.

Attribute value data types

Data Type	Object	Description
Strings	NSString	Used for such things as display names
Floating-point values	NSNumber	Scalar values such as intensity levels and radii
Vectors	CIVector	Specify positions, areas, and color values; can have 2, 3, or 4 elements, each of which is a floating-point number
Colors	CIColor	Contain color values and a color space in which to interpret the values
Images	CIImage	Lightweight objects that specify image “recipes”
Transforms	NSDataon iOS NSAffineTransformon OS X	An affine transformation to apply to an image

Creating a Core Image Context

 Methods that create a Core Image context

Context	Renderer	Supported Platform
contextWithOptions:	CPU or GPU	iOS
contextWithCGContext:options: NSGraphicsContext	CPU or GPU	OS X
contextWithEAGLContext: contextWithEAGLContext:options:	GPU	iOS
contextWithCGLContext:pixelFormat:options: contextWithCGLContext:pixelFormat:colorSpace:options:	GPU	OS X

creating a Core Image Context on iOS When You Don’t Need Real-Time Performance

you can create a CIContext object as follows:

CIContext *context = [CIContext contextWithOptions:nil];

Creating a Core Image Context on iOS When You Need Real-Time Performanc

myEAGLContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];

Creating a CIContext on iOS for real-time performance

NSMutableDictionary *options = [[NSMutableDictionary alloc] init];

[options setObject: [NSNull null] forKey: kCIContextWorkingColorSpace];

myContext = [CIContext contextWithEAGLContext:myEAGLContext options:options];

Creating a CIImage Object

Methods used to create a CIImage object from existing image sources

Image source	Methods	Platform
URL	imageWithContentsOfURL: imageWithContentsOfURL:options:	iOS, OS X
Quartz 2D image (CGImageRef)	imageWithCGImage: imageWithCGImage:options:	iOS, OS X
Bitmap data	imageWithBitmapData:bytesPerRow:size:format:colorSpace: imageWithImageProvider:size:format:colorSpace:options:	iOS, OS X
Encoded data (an image in memory)	imageWithData: imageWithData:options:	iOS, OS X
CIImageProvider	imageWithImageProvider:size:format:colorSpace:options:	iOS, OS X
OpenGL texture	imageWithTexture:size:flipped:colorSpace:	OS X, iOS 6.0 and later
CVPixelBuffer	imageWithCVPixelBuffer: imageWithCVPixelBuffer:options:	iOS
CVPixelBuffer	imageWithIOSurface: imageWithIOSurface:options:	OS X
CVImageBuffer	imageWithCVImageBuffer: imageWithCVImageBuffer:options:	OS X
Quartz 2D layer (CGLayerRef)	imageWithCGLayer: imageWithCGLayer:options:	OS X
NSCIImageRep	initWithBitmapImageRep: See NSCIImageRep Class Reference for more information on this AppKit addition.	OS X
Except where noted, iOS methods are available starting with iOS v5.0.

Creating a CIFilter Object and Setting Values

The  filterWithName:  method creates a filter whose type is specified by the  name  argument.Defaults are set for you on iOS but not on OS X.

If you don’t know the input parameters for a filter, you can get an array of them using the method inputKeys. 

hueAdjust = [CIFilter filterWithName:@"CIHueAdjust"];

[hueAdjust setValue: myCIImage forKey: @"inputImage"];

[hueAdjust setValue: [NSNumber numberWithFloat: 2.094]

forKey: @"inputAngle"];

or

hueAdjust = [CIFilter filterWithName:@"CIHueAdjust"] keysAndValues:

@"inputImage",myCIImage,

@"inputAngle, [NSNumber numberWithFloat: 2.094],

nil];

Getting the Output Image

You get the output image by retrieving the value for the outputImage key:

CIImage *result = [hueAdjust valueForKey: @"outputImage"];

Rendering the Resulting Output Image

Method	Use
drawImage:inRect:fromRect:	Renders a region of an image to a rectangle in the context destination. On iOS, this method renders only to aCIContext object that is created withcontextWithEAGLContext:. On OS X, the dimensions of the destination rectangle are in points if the CIContextobject is created with a CGContextRef. The dimensions are in points if the CIContextobject is created with a CGLContext object.
createCGImage:fromRect: createCGImage:fromRect:format:colorSpace:	Create a Quartz 2D image from a region of aCIImage object. (iOS and OS X)
render:toBitmap:rowBytes:bounds:format:colorSpace:	Renders a CIImage object into a bitmap. (iOS and OS X)s
createCGLayerWithSize:info:	Creates a CGLayer object renders theCIImage object into the layer. (OSX only)
render:toCVPixelBuffer: render:toCVPixelBuffer:bounds:colorSpace:	Renders the CIImage object into a Core Video pixel buffer. (iOS only)

[myContext drawImage:result inRect:destinationRect fromRect:contextRect];

Maintaining Thread Safety

CIContext and CIImage objects are immutable, which means each can be shared safely among threads. Multiple threads can use the same GPU or CPU CIContext object to render CIImage objects. However, this is not the case for CIFilter objects, which are mutable. A CIFilter object cannot be shared safely among threads. If your app is multithreaded, each thread must create its own CIFilter objects. Otherwise, your app could behave unexpectedly.

Chaining Filters

 Creating, setting up, and applying a gloom filter

gloom = [CIFilter filterWithName:@"CIGloom"];

[gloom setDefaults]; // 1

[gloom setValue: result forKey: @"inputImage"];

[gloom setValue: [NSNumber numberWithFloat: 25]

forKey: @"inputRadius"]; // 2

[gloom setValue: [NSNumber numberWithFloat: 0.75]

forKey: @"inputIntensity"]; // 3

result = [gloom valueForKey: @"outputImage"];

Detecting Faces

Creating a face detector

CIContext *context = [CIContext contextWithOptions:nil]; // 1

NSDictionary *opts = [NSDictionary dictionaryWithObject:CIDetectorAccuracyHigh

forKey:CIDetectorAccuracy]; // 2

CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeFace

context:context

options:opts]; // 3

opts = [NSDictionary dictionaryWithObject:

[[myImage properties] valueForKey:kCGImagePropertyOrientation;

forKey:CIDetectorImageOrientation]]; // 4

NSArray *features = [detector featuresInImage:myImage

options:opts]; // 5

Examining face feature bounds

for (CIFaceFeature *f in features)

{

NSLog(NSStringFromRect(f.bounds));

if (f.hasLeftEyePosition)

printf("Left eye %g %g\n", f.leftEyePosition.x.

f.leftEyePosition.y);

if (f.hasRightEyePosition)

printf("Right eye %g %g\n", f.rightEyePosition.x.

f.rightEyePosition.y);

if (f.hasmouthPosition)

printf("Mouth %g %g\n", f.mouthPosition.x.

f.mouthPosition.y);

}

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