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# CIColorKernel

A GPU-based image-processing routine that processes only the color information in images, used to create custom Core Image filters.

```
class CIColorKernel
```

## Overview

The kernel language routine for a color kernel has the following characteristics:

- Its return type is `vec4` (Core Image Kernel Language) or `float4` (Metal Shading Language); that is, it returns a pixel color for the output image.
- It may use zero or more input images. Each input image is represented by a parameter of type `__sample` (Core Image Kernel Language) or `sample_t` (Metal Shading Language), which can be treated as a single pixel color of type `vec4` (Core Image Kernel Language) or `float4` (Metal Shading Language);.

A color kernel routine receives as input single-pixel colors (one sampled from each input image) and computes a final pixel color (output using the `return` keyword). For example, the Metal Shading Language source below implements a filter that passes through its input image unchanged.

```c
#include <CoreImage/CoreImage.h>
 
extern "C" {
    namespace coreimage {
        float4 do_nothing(sample_t s) {
            return s;
        }
    }
}
```

The equivalent code in Core Image Kernel Language is:

```c
kernel vec4 do_nothing(__sample s) {
    return s.rgba;
}
```

The Core Image Kernel Language is a dialect of the OpenGL Shading Language. See [Core Image Kernel Language Reference](https://developer.apple.com/library/archive/documentation/GraphicsImaging/Reference/CIKernelLangRef/Introduction/Introduction.html#//apple_ref/doc/uid/TP40004397) and [Core Image Programming Guide](https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/CoreImaging/ci_intro/ci_intro.html#//apple_ref/doc/uid/TP30001185) for more details.

## Topics

### Creating a Kernel

[`init(source:)`](/documentation/CoreImage/CIColorKernel/init(source:))

Creates a color kernel object from the specified kernel source code.

### Applying a Kernel to Filter an Image

[`apply(extent:arguments:)`](/documentation/CoreImage/CIColorKernel/apply(extent:arguments:))

Creates a new image using the kernel and specified arguments.


---

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