''' Purpose: provide means of converting an image to grayscale
'''

from PIL import Image

def average( original ) :
    ''' produce a grayscale 
    '''

    # get image dimensions
    ow, oh = original.size          # get the dimensions of the original
    nw, nh = ow, oh                 # new image has same dimensions

    # create new image 
    new_image = Image.new( 'RGB', (nw, nh ) )

    # consider every pixel
    for nx in range( 0, nw ) :          # consider every possible x value
        for ny in range( 0, nh ) :      # consider every possible y value
            # get spots of interest
            nspot = ( nx, ny )
            ospot = ( nx, ny )

            # get color of the original pixel
            opixel  = original.getpixel( ospot )
            r, g, b = opixel

            # get the gray equivalent
            a = ( r + g + b ) // 3

            npixel = ( a, a, a )

            # set new image pixel color 
            new_image.putpixel( nspot, npixel )

    # return the result
    return new_image

def ntsc( original ) :
    ''' produce a grayscale pixels to their monochrome luminances, using NTSC
        formula mapping (r, g, b) to (m, m, m), where m = .299r + .587g + .114b
    '''

    # get image dimensions
    ow, oh = original.size          # get the dimensions of the original
    nw, nh = ow, oh                 # new image has same dimensions

    # create new image 
    new_image = Image.new( 'RGB', (nw, nh ) )

    # consider every pixel
    for nx in range( 0, nw ) :          # consider every possible x value
        for ny in range( 0, nh ) :      # consider every possible y value
            # get spots of interest
            nspot = ( nx, ny )
            ospot = ( nx, ny )

            # get color of the original pixel
            opixel  = original.getpixel( ospot )
            r, g, b = opixel

            # get the gray equivalent
            m = int( .299*r + .587*g + .114*b )
            npixel = ( m, m, m )

            # set new image pixel color 
            new_image.putpixel( nspot, npixel )

    # return the result
    return new_image

if ( __name__ == '__main__' ) :

    import url
    import grayscale

    # get web image of interest
    link = "http://www.cs.virginia.edu/~cs1112/images/mandrill/full.png"

    im = url.get_image( link )

    # get grayed versions

    grayed1 = grayscale.average( im )
    grayed1.show()

    grayed2 = grayscale.ntsc( im )
    grayed2.show()