Module: Origami::Filter::Predictor

Defined in:
lib/origami/filters/predictors.rb

Constant Summary collapse

NONE = 
1
TIFF = 
2
PNG_NONE = 
10
PNG_SUB = 
11
PNG_UP = 
12
PNG_AVERAGE = 
13
PNG_PAETH = 
14
PNG_OPTIMUM = 
15

Class Method Summary collapse

Class Method Details

.do_png_post_prediction(data, bpp, bpr) ⇒ Object 



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# File 'lib/origami/filters/predictors.rb', line 100

def self.do_png_post_prediction(data, bpp, bpr)
    result = ""
    uprow = "\0" * bpr
    thisrow = "\0" * bpr
    nrows = (data.size + bpr - 1) / bpr

    nrows.times do |irow|
        line = data[irow * bpr, bpr]
        predictor = 10 + line[0].ord
        line[0] = "\0"

        for i in (1..line.size-1)
            up = uprow[i].ord

            if bpp > i
                left = upleft = 0
            else
                left = line[i-bpp].ord
                upleft = uprow[i-bpp].ord
            end

            case predictor
            when PNG_NONE
                thisrow = line
            when PNG_SUB
                thisrow[i] = ((line[i].ord + left) & 0xFF).chr
            when PNG_UP
                thisrow[i] = ((line[i].ord + up) & 0xFF).chr
            when PNG_AVERAGE
                thisrow[i] = ((line[i].ord + ((left + up) / 2)) & 0xFF).chr
            when PNG_PAETH
                p = left + up - upleft
                pa, pb, pc = (p - left).abs, (p - up).abs, (p - upleft).abs

                thisrow[i] = ((line[i].ord +
                    case [ pa, pb, pc ].min
                    when pa then left
                    when pb then up
                    when pc then upleft
                    end
                ) & 0xFF).chr
            else
                unless Origami::OPTIONS[:ignore_png_errors]
                    raise PredictorError.new("Unknown PNG predictor : #{predictor}", input_data: data, decoded_data: result)
                end

                # behave as PNG_NONE
                thisrow = line
            end
        end

        result << thisrow[1..-1]
        uprow = thisrow
    end

    result
end

.do_png_pre_prediction(data, predictor, bpp, bpr) ⇒ Object 



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# File 'lib/origami/filters/predictors.rb', line 158

def self.do_png_pre_prediction(data, predictor, bpp, bpr)
    result = ""
    nrows = data.size / bpr

    line = "\0" + data[-bpr, bpr]

    (nrows-1).downto(0) do |irow|
        uprow =
        if irow == 0
            "\0" * (bpr+1)
        else
            "\0" + data[(irow-1)*bpr,bpr]
        end

        bpr.downto(1) do |i|
            up = uprow[i].ord
            left = line[i-bpp].ord
            upleft = uprow[i-bpp].ord

            case predictor
            when PNG_SUB
                line[i] = ((line[i].ord - left) & 0xFF).chr
            when PNG_UP
                line[i] = ((line[i].ord - up) & 0xFF).chr
            when PNG_AVERAGE
                line[i] = ((line[i].ord - ((left + up) / 2)) & 0xFF).chr
            when PNG_PAETH
                p = left + up - upleft
                pa, pb, pc = (p - left).abs, (p - up).abs, (p - upleft).abs

                line[i] = ((line[i].ord -
                    case [ pa, pb, pc ].min
                    when pa then left
                    when pb then up
                    when pc then upleft
                    end
                ) & 0xFF).chr
            when PNG_NONE
            else
                raise PredictorError.new("Unsupported PNG predictor : #{predictor}", input_data: data)
            end
        end

        line[0] = (predictor - 10).chr
        result = line + result

        line = uprow
    end

    result
end

.do_post_prediction(data, predictor: NONE, colors: 1, bpc: 8, columns: 1) ⇒ Object 



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# File 'lib/origami/filters/predictors.rb', line 71

def self.do_post_prediction(data, predictor: NONE, colors: 1, bpc: 8, columns: 1)
    return data if predictor == NONE

    unless (1..4) === colors
        raise PredictorError.new("Colors must be between 1 and 4", input_data: data)
    end

    unless [1,2,4,8,16].include?(bpc)
        raise PredictorError.new("BitsPerComponent must be in 1, 2, 4, 8 or 16", input_data: data)
    end

    # components per line
    nvals = columns * colors

    # bytes per pixel
    bpp = (colors * bpc + 7) >> 3

    # bytes per row
    bpr = ((nvals * bpc + 7) >> 3) + 1

    if predictor == TIFF
        do_tiff_post_prediction(data, colors, bpc, columns)
    elsif predictor >= 10 # PNG
        do_png_post_prediction(data, bpp, bpr)
    else
        raise PredictorError.new("Unknown predictor : #{predictor}", input_data: data)
    end
end

.do_pre_prediction(data, predictor: NONE, colors: 1, bpc: 8, columns: 1) ⇒ Object 



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# File 'lib/origami/filters/predictors.rb', line 38

def self.do_pre_prediction(data, predictor: NONE, colors: 1, bpc: 8, columns: 1)
    return data if predictor == NONE

    unless (1..4) === colors.to_i
        raise PredictorError.new("Colors must be between 1 and 4", input_data: data)
    end

    unless [1,2,4,8,16].include?(bpc.to_i)
        raise PredictorError.new("BitsPerComponent must be in 1, 2, 4, 8 or 16", input_data: data)
    end

    # components per line
    nvals = columns * colors

    # bytes per pixel
    bpp = (colors * bpc + 7) >> 3

    # bytes per row
    bpr = (nvals * bpc + 7) >> 3

    unless data.size % bpr == 0
        raise PredictorError.new("Invalid data size #{data.size}, should be multiple of bpr=#{bpr}", input_data: data)
    end

    if predictor == TIFF
        do_tiff_pre_prediction(data, colors, bpc, columns)
    elsif predictor >= 10 # PNG
        do_png_pre_prediction(data, predictor, bpp, bpr)
    else
        raise PredictorError.new("Unknown predictor : #{predictor}", input_data: data)
    end
end

.do_tiff_post_prediction(data, colors, bpc, columns) ⇒ Object

:nodoc:



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# File 'lib/origami/filters/predictors.rb', line 210

def self.do_tiff_post_prediction(data, colors, bpc, columns) #:nodoc:
    bpr = (colors * bpc * columns + 7) >> 3
    nrows = data.size / bpr
    bitmask = (1 << bpc) - 1
    result = Utils::BitWriter.new

    nrows.times do |irow|
        line = Utils::BitReader.new(data[irow * bpr, bpr])

        pixel = ::Array.new(colors, 0)
        columns.times do
            diffpixel = ::Array.new(colors) { line.read(bpc) }
            pixel = pixel.zip(diffpixel).map!{|c, diff| (c + diff) & bitmask}

            pixel.each do |c|
                result.write(c, bpc)
            end
        end

        result.final
    end

    result.final.to_s
end

.do_tiff_pre_prediction(data, colors, bpc, columns) ⇒ Object

:nodoc:



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# File 'lib/origami/filters/predictors.rb', line 235

def self.do_tiff_pre_prediction(data, colors, bpc, columns) #:nodoc:
    bpr = (colors * bpc * columns + 7) >> 3
    nrows = data.size / bpr
    bitmask = (1 << bpc) - 1
    result = Utils::BitWriter.new

    nrows.times do |irow|
        line = Utils::BitReader.new(data[irow * bpr, bpr])

        diffpixel = ::Array.new(colors, 0)
        columns.times do
            pixel = ::Array.new(colors) { line.read(bpc) }
            diffpixel = diffpixel.zip(pixel).map!{|diff, c| (c - diff) & bitmask}

            diffpixel.each do |c|
                result.write(c, bpc)
            end
        end

        result.final
    end

    result.final.to_s
end