fs = require 'streamline-fs' Data = '../data' zlib = require 'zlib' class PNG @open: (_, filename) -> contents = fs.readFile filename, _ data = new Data(contents) new PNG(data) constructor: (@data) -> data.pos = 8 # Skip the default header @palette = [] @imgData = [] @transparency = {} loop chunkSize = data.readUInt32() section = data.readString(4) switch section when 'IHDR' # we can grab interesting values from here (like width, height, etc) @width = data.readUInt32() @height = data.readUInt32() @bits = data.readByte() @colorType = data.readByte() @compressionMethod = data.readByte() @filterMethod = data.readByte() @interlaceMethod = data.readByte() when 'PLTE' @palette = data.read(chunkSize) when 'IDAT' for i in [0...chunkSize] @imgData.push data.readByte() when 'tRNS' # This chunk can only occur once and it must occur after the # PLTE chunk and before the IDAT chunk. @transparency = {} switch @colorType when 3 # Indexed color, RGB. Each byte in this chunk is an alpha for # the palette index in the PLTE ("palette") chunk up until the # last non-opaque entry. Set up an array, stretching over all # palette entries which will be 0 (opaque) or 1 (transparent). @transparency.indexed = data.read(chunkSize) short = 255 - @transparency.indexed.length if short > 0 @transparency.indexed.push 255 for i in [0...short] when 0 # Greyscale. Corresponding to entries in the PLTE chunk. # Grey is two bytes, range 0 .. (2 ^ bit-depth) - 1 @transparency.grayscale = data.read(chunkSize)[0] when 2 # True color with proper alpha channel. @transparency.rgb = data.read(chunkSize) when 'IEND' # we've got everything we need! @colors = switch @colorType when 0, 3, 4 then 1 when 2, 6 then 3 @hasAlphaChannel = @colorType in [4, 6] colors = @colors + if @hasAlphaChannel then 1 else 0 @pixelBitlength = @bits * colors @colorSpace = switch @colors when 1 then 'DeviceGray' when 3 then 'DeviceRGB' @imgData = new Buffer @imgData return else # unknown (or unimportant) section, skip it data.pos += chunkSize data.pos += 4 # Skip the CRC return object: (_, document) -> obj = document.ref Type: 'XObject' Subtype: 'Image' BitsPerComponent: @bits Width: @width Height: @height Length: @imgData.length Filter: 'FlateDecode' unless @hasAlphaChannel obj.data['DecodeParms'] = Predictor: 15 Colors: @colors BitsPerComponent: @bits Columns: @width if @palette.length is 0 obj.data['ColorSpace'] = @colorSpace else # embed the color palette in the PDF as an object stream palette = document.ref Length: @palette.length palette.add new Buffer(@palette) # build the color space array for the image obj.data['ColorSpace'] = ['Indexed', 'DeviceRGB', (@palette.length / 3) - 1, palette] # For PNG color types 0, 2 and 3, the transparency data is stored in # a dedicated PNG chunk. if @transparency.grayscale # Use Color Key Masking (spec section 4.8.5) # An array with N elements, where N is two times the number of color components. val = @transparency.greyscale obj.data['Mask'] = [val, val] else if @transparency.rgb # Use Color Key Masking (spec section 4.8.5) # An array with N elements, where N is two times the number of color components. rgb = @transparency.rgb mask = [] for x in rgb mask.push x, x obj.data['Mask'] = mask else if @transparency.indexed # Create a transparency SMask for the image based on the data # in the PLTE and tRNS sections. See below for details on SMasks. @loadIndexedAlphaChannel(_) # For PNG color types 4 and 6, the transparency data is stored as a alpha # channel mixed in with the main image data. Separate this data out into an # SMask object and store it separately in the PDF. if @hasAlphaChannel @splitAlphaChannel(_) obj.data['Length'] = @imgData.length if @alphaChannel sMask = document.ref Type: 'XObject' Subtype: 'Image' Height: @height Width: @width BitsPerComponent: 8 Length: @alphaChannel.length Filter: 'FlateDecode' ColorSpace: 'DeviceGray' Decode: [0, 1] sMask.add @alphaChannel obj.data['SMask'] = sMask # add the actual image data obj.add @imgData return obj decodePixels: (_) -> data = zlib.inflate @imgData, ~_ pixelBytes = @pixelBitlength / 8 scanlineLength = pixelBytes * @width row = 0 pixels = [] length = data.length pos = 0 while pos < length filter = data[pos++] i = 0 rowData = [] switch filter when 0 # None while i < scanlineLength rowData[i++] = data[pos++] when 1 # Sub while i < scanlineLength byte = data[pos++] left = if i < pixelBytes then 0 else rowData[i - pixelBytes] rowData[i++] = (byte + left) % 256 when 2 # Up while i < scanlineLength byte = data[pos++] col = (i - (i % pixelBytes)) / pixelBytes upper = if row is 0 then 0 else pixels[row - 1][col][i % pixelBytes] rowData[i++] = (upper + byte) % 256 when 3 # Average while i < scanlineLength byte = data[pos++] col = (i - (i % pixelBytes)) / pixelBytes left = if i < pixelBytes then 0 else rowData[i - pixelBytes] upper = if row is 0 then 0 else pixels[row - 1][col][i % pixelBytes] rowData[i++] = (byte + Math.floor((left + upper) / 2)) % 256 when 4 # Paeth while i < scanlineLength byte = data[pos++] col = (i - (i % pixelBytes)) / pixelBytes left = if i < pixelBytes then 0 else rowData[i - pixelBytes] if row is 0 upper = upperLeft = 0 else upper = pixels[row - 1][col][i % pixelBytes] upperLeft = if col is 0 then 0 else pixels[row - 1][col - 1][i % pixelBytes] p = left + upper - upperLeft pa = Math.abs(p - left) pb = Math.abs(p - upper) pc = Math.abs(p - upperLeft) if pa <= pb and pa <= pc paeth = left else if pb <= pc paeth = upper else paeth = upperLeft rowData[i++] = (byte + paeth) % 256 else throw new Error "Invalid filter algorithm: " + filter s = [] for i in [0...rowData.length] by pixelBytes s.push rowData.slice(i, i + pixelBytes) pixels.push(s) row += 1 return pixels splitAlphaChannel:(_) -> pixels = @decodePixels(_) colorByteSize = @colors * @bits / 8 alphaByteSize = 1 pixelCount = @width * @height imgData = new Buffer(pixelCount * colorByteSize) alphaChannel = new Buffer(pixelCount) p = a = 0 for row in pixels for pixel in row imgData[p++] = pixel[i] for i in [0...colorByteSize] alphaChannel[a++] = pixel[colorByteSize] @imgData = zlib.deflate imgData, ~_ @alphaChannel = zlib.deflate alphaChannel, ~_ decodePalette: -> palette = @palette transparency = @transparency.indexed ? [] decodingMap = [] index = 0 for i in [0...palette.length] by 3 alpha = transparency[index++] ? 255 pixel = palette.slice(i, i + 3).concat(alpha) decodingMap.push pixel return decodingMap loadIndexedAlphaChannel:(_) -> palette = @decodePalette() pixels = @decodePixels(_) pixelCount = @width * @height alphaChannel = new Buffer(pixelCount) i = 0 for row in pixels for pixel in row pixel = pixel[0] alphaChannel[i++] = palette[pixel][3] @alphaChannel = zlib.deflate alphaChannel, ~_ module.exports = PNG