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 function parameter 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 parameter can return up to four number values, which become the new r, g, b and a values of the pixel. If the function returns fewer values, the remaining components are set to 0.

Function

Synopsis

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

ImageData:mapPixel( pixelFunction )

Arguments

function pixelFunction

Function parameter to apply to every pixel.

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