# Processing an Image Using Built-in Filters Apply effects such as sepia tint, highlight strengthening, and scaling to images. ## Discussion You can add effects to images by applying Core Image filters to [`CIImage`](/documentation/CoreImage/CIImage) objects. Figure 1 shows three filters chained together to achieve a cumulative effect: 1. Apply the sepia filter to tint an image with a reddish-brown hue. 2. Add the bloom filter to accentuate highlights. 3. Use the Lanczos scale filter to scale an image down.  ### Create a Context [`CIImage`](/documentation/CoreImage/CIImage) processing occurs in a [`CIContext`](/documentation/CoreImage/CIContext) object. Creating a [`CIContext`](/documentation/CoreImage/CIContext) is expensive, so create one during your initial setup and reuse it throughout your app. ```swift CIContext* context = [CIContext context]; ``` ### Load an Image to Process The next step is to load an image to process. This example loads an image from the project bundle. ```swift NSURL* imageURL = [[NSBundle mainBundle] URLForResource:@"YourImageName" withExtension:@"png"]; CIImage* originalCIImage = [CIImage imageWithContentsOfURL:imageURL]; self.imageView.image = [UIImage imageWithCIImage:originalCIImage]; ``` The [`CIImage`](/documentation/CoreImage/CIImage) object isn’t itself a displayable image, but rather image data. To display it, you must convert it to another type, such as . ### Apply Built-In Core Image Filters A [`CIFilter`](/documentation/CoreImage/CIFilter-swift.class) represents a single operation or recipe for a particular effect. To process a [`CIImage`](/documentation/CoreImage/CIImage) object, pass it through [`CIFilter`](/documentation/CoreImage/CIFilter-swift.class) objects. You can subclass [`CIFilter`](/documentation/CoreImage/CIFilter-swift.class) or draw from the existing library of built-in filters. #### Tint Reddish-Brown with the Sepia Filter Although you can chain filters without separating them into functions, the following example shows how to configure a single [`CIFilter`](/documentation/CoreImage/CIFilter-swift.class), the [`sepiaTone()`](/documentation/CoreImage/CIFilter-swift.class/sepiaTone()) filter. ```swift - (CIImage*) sepiaFilterImage: (CIImage*)inputImage withIntensity:(CGFloat)intensity { CIFilter* sepiaFilter = CIFilter.sepiaToneFilter; sepiaFilter.inputImage = inputImage; sepiaFilter.intensity = intensity; return sepiaFilter.outputImage; } ``` To pass the image through the filter, call the sepia filter function. ```swift CIImage* sepiaCIImage = [self sepiaFilterImage:originalCIImage withIntensity:0.9]; ``` You can check the intermediate result at any point in the filter chain by converting from [`CIImage`](/documentation/CoreImage/CIImage) to a . You can then assign this to a for display. ```swift _imageView.image = [UIImage imageWithCIImage:sepiaCIImage]; ``` #### Strengthen Highlights with the Bloom Filter The bloom filter accentuates the highlights of an image. You can apply it as part of a chain without factoring it into a separate function, but this example encapsulates its functionality into a function. ```swift - (CIImage*) bloomFilterImage: (CIImage*)inputImage withIntensity:(CGFloat)intensity radius:(CGFloat)radius { CIFilter* bloomFilter = CIFilter.bloomFilter; bloomFilter.inputImage = inputImage; bloomFilter.intensity = intensity; bloomFilter.radius = radius; return bloomFilter.outputImage; } ``` Like the sepia filter, the intensity of the bloom filter’s effect ranges between 0 and 1, with 1 being the most intense effect. The bloom filter has an additional r`adius` parameter to determine how much the glowing regions expand. Experiment with a range to values to fine tune the effect, or assign the input parameter to a control like a to allow your users to tweak its values. > Note: > The ``doc://com.apple.coreimage/documentation/CoreImage/CIFilter-swift.class/gloom()`` filter performs the opposite effect. To display the output, convert the [`CIImage`](/documentation/CoreImage/CIImage) to a . ```swift CIImage* bloomCIImage = [self bloomFilterImage:sepiaCIImage withIntensity:1 radius:10]; _filteredImageView.image = [UIImage imageWithCIImage:bloomCIImage]; ``` #### Scale Image Size with the Lanczos Scale Filter Apply the [`lanczosScaleTransform()`](/documentation/CoreImage/CIFilter-swift.class/lanczosScaleTransform()) to obtain a high-quality downsampling of the image, preserving the original image’s aspect ratio through the [`lanczosScaleTransform()`](/documentation/CoreImage/CIFilter-swift.class/lanczosScaleTransform()) filter’s parameter `aspectRatio`. For built-in Core Image filters, calculate the aspect ratio as the image’s width over height. ```swift CGFloat imageWidth = originalUIImage.size.width; CGFloat imageHeight = originalUIImage.size.height; CGFloat aspectRatio = imageHeight / imageWidth; CIImage* scaledCIImage = [self scaleFilterImage:bloomCIImage withAspectRatio:aspectRatio scale:0.05]; ``` Like other built-in filters, the [`lanczosScaleTransform()`](/documentation/CoreImage/CIFilter-swift.class/lanczosScaleTransform()) filter also outputs its result as a [`CIImage`](/documentation/CoreImage/CIImage). ```swift - (CIImage*) scaleFilterImage: (CIImage*)inputImage withAspectRatio:(CGFloat)aspectRatio scale:(CGFloat)scale { CIFilter* scaleFilter = CIFilter.lanczosScaleTransformFilter; scaleFilter.inputImage = inputImage; scaleFilter.scale = scale; scaleFilter.aspectRatio = aspectRatio; return scaleFilter.outputImage; } ``` > Important: > To optimize computation, Core Image doesn’t actually render any intermediate ``doc://com.apple.coreimage/documentation/CoreImage/CIImage`` result until you force the ``doc://com.apple.coreimage/documentation/CoreImage/CIImage`` to display its content onscreen, as you might do using . ```swift _imageView.image = [UIImage imageWithCIImage:scaledCIImage]; ``` > Note: > Core Image optimizes filtering by reordering the three chained filters and concatenating them into a single image processing kernel, saving computation and rendering cycles. In addition to trying out the built-in filters for a fixed effect, you can combine filters in certain Filter Recipes to accomplish tasks such as [Applying a Chroma Key Effect](/documentation/CoreImage/applying-a-chroma-key-effect), [Selectively Focusing on an Image](/documentation/CoreImage/selectively-focusing-on-an-image), [Customizing Image Transitions](/documentation/CoreImage/customizing-image-transitions), and [Simulating Scratchy Analog Film](/documentation/CoreImage/simulating-scratchy-analog-film). --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)