# ImageData:mapPixel

Transform an image by applying a function to every pixel.

This function is a higher order function. It takes another function as a parameter, and calls it once for each pixel in the ImageData.

The passed function is called with six parameters for each pixel in turn. The parameters are numbers that represent the x and y coordinates of the pixel and its red, green, blue and alpha values. The function should return the new red, green, blue, and alpha values for that pixel.

    function pixelFunction(x, y, r, g, b, a)
        -- template for defining your own pixel mapping function
        -- perform computations giving the new values for r, g, b and a
        -- ...
        return r, g, b, a
    end

## Function

### Synopsis

    ImageData:mapPixel( pixelFunction )

### Arguments

`function pixelFunction`
  Function to apply to every pixel.

### Returns

Nothing.

## Function

Available since LÖVE 0.9.0
This variant is not supported in earlier versions.

### Synopsis

    ImageData:mapPixel( pixelFunction, x, y, width, height )

### Arguments

`function pixelFunction`
  Function to apply to every pixel.
`number x`
  The x-axis of the top-left corner of the area within the ImageData to apply the function to.
`number y`
  The y-axis of the top-left corner of the area within the ImageData to apply the function to.
`number width`
  The width of the area within the ImageData to apply the function to.
`number height`
  The height of the area within the ImageData to apply the function to.

### Returns

Nothing.

## Examples

### Brighten an image:

    function brighten( x, y, r, g, b, a )
       r = math.min(r * 3, 255)
       g = math.min(g * 3, 255)
       b = math.min(b * 3, 255)
       return r,g,b,a
    end

    imageData:mapPixel( brighten )

### Add colored stripes to an image:

    function stripey( x, y, r, g, b, a )
       r = math.min(r * math.sin(x*100)*2, 255)
       g = math.min(g * math.cos(x*150)*2, 255)
       b = math.min(b * math.sin(x*50)*2, 255)
       return r,g,b,a
    end

    imageData:mapPixel( stripey )

source: http://khason.net/blog/hlsl-pixel-shader-effects-tutorial/

## See Also

- ImageData

##

Category:

- Functions