png-unfilter-line ( width prev curr filter -- curr' )

Vocabulary

images.png

Inputs

width	an object
prev	an object
curr	an object
filter	an object

Outputs

curr'

an object

Definition

USING: combinators kernel math math.bitwise sequences ;

IN: images.png

:: png-unfilter-line ( width prev curr filter -- curr' )
    prev :> c prev width tail-slice
    :> b curr :> a curr width tail-slice
    :> x x length <iota> filter {
        { filter-none [ drop ] }
        {
            filter-sub
            [
                [| n | n x nth n a nth + 256 wrap n x set-nth ]
                each
            ]
        }
        {
            filter-up
            [
                [| n | n x nth n b nth + 256 wrap n x set-nth ]
                each
            ]
        }
        {
            filter-average
            [
                [| n |
                    n x nth n a nth n b nth + 2/ + 256 wrap
                    n x set-nth
                ] each
            ]
        }
        {
            filter-paeth
            [
                [| n |
                    n x nth n a nth n b nth n c nth paeth +
                    256 wrap n x set-nth
                ] each
            ]
        }
        [ bad-filter ]
    } case curr width tail ;