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

In versions prior to 11.0, color component values were within the range of 0 to 255 instead of 0 to 1.

Function

Synopsis

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

Arguments

function pixelFunction

Function to apply to every pixel.

number x (0) Available since 0.9.0

The x-axis of the top-left corner of the area within the ImageData to apply the function to.

number y (0) Available since 0.9.0

The y-axis of the top-left corner of the area within the ImageData to apply the function to.

number width (ImageData:getWidth()) Available since 0.9.0

The width of the area within the ImageData to apply the function to.

number height (ImageData:getHeight()) Available since 0.9.0

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, 1)
   g = math.min(g * 3, 1)
   b = math.min(b * 3, 1)
   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, 1)
   g = math.min(g * math.cos(x*150)*2, 1)
   b = math.min(b * math.sin(x*50)*2, 1)
   return r,g,b,a
end
 
imageData:mapPixel( stripey )

source: http://khason.net/blog/hlsl-pixel-shader-effects-tutorial/ (broken 11/16. See blogs.microsoft.co.il or archive.org mirrors.)

See Also

• ImageData