You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
206 lines
8.4 KiB
Racket
206 lines
8.4 KiB
Racket
#lang debug racket/base
|
|
(require
|
|
racket/class
|
|
"reference.rkt"
|
|
"core.rkt"
|
|
fontland/zlib
|
|
racket/dict
|
|
racket/list
|
|
racket/file
|
|
racket/draw
|
|
sugar/unstable/dict)
|
|
|
|
#|
|
|
https://github.com/mbutterick/pdfkit/blob/master/lib/image/png.coffee
|
|
|#
|
|
|
|
(provide (all-defined-out))
|
|
|
|
(struct $png $img (image pixel-bit-length img-data alpha-channel)
|
|
#:transparent #:mutable)
|
|
|
|
(define (make-png data [label #f])
|
|
(define image (read-png data))
|
|
(define pixel-bit-length (hash-ref image 'pixelBitlength))
|
|
(define width (hash-ref image 'width))
|
|
(define height (hash-ref image 'height))
|
|
(define img-data (hash-ref image 'imgData))
|
|
(define alpha-channel #f)
|
|
(define obj #f)
|
|
($png data label width height obj png-embed image pixel-bit-length img-data alpha-channel))
|
|
|
|
(define (png-embed png)
|
|
(unless ($img-ref png)
|
|
(set-$img-ref! png
|
|
(make-ref
|
|
(mhash 'Type 'XObject
|
|
'Subtype 'Image
|
|
'BitsPerComponent (hash-ref ($png-image png) 'bits)
|
|
'Width ($img-width png)
|
|
'Height ($img-height png)
|
|
'Filter 'FlateDecode)))
|
|
|
|
(unless (hash-ref ($png-image png) 'hasAlphaChannel #f)
|
|
(define params (make-ref
|
|
(mhash 'Predictor 15
|
|
'Colors (hash-ref ($png-image png) 'colors)
|
|
'BitsPerComponent (hash-ref ($png-image png) 'bits)
|
|
'Columns ($img-width png))))
|
|
(dict-set! ($img-ref png) 'DecodeParms params)
|
|
(ref-end params))
|
|
|
|
(cond
|
|
[(hash-has-key? ($png-image png) 'palette)
|
|
;; embed the color palette in the PDF as an object stream
|
|
(define palette-ref (make-ref))
|
|
(ref-write palette-ref (hash-ref ($png-image png) 'palette))
|
|
(ref-end palette-ref)
|
|
;; build the color space array for the image
|
|
(dict-set! ($img-ref png) 'Colorspace
|
|
(list 'Indexed 'DeviceRGB (sub1 (/ (bytes-length (hash-ref ($png-image png) 'palette)) 3)) palette-ref))]
|
|
[else (dict-set! ($img-ref png) 'ColorSpace 'DeviceRGB)])
|
|
|
|
|
|
(cond
|
|
[(hash-ref ($png-image png) 'transparency #f)
|
|
(cond
|
|
[(hash-ref (hash-ref ($png-image png) 'transparency) 'grayscale #f)
|
|
(error 'transparency-grayscale-not-implemented)]
|
|
[(hash-ref (hash-ref ($png-image png) 'transparency) 'rgb #f)
|
|
(error 'transparency-rgb-not-implemented)]
|
|
[(hash-ref (hash-ref ($png-image png) 'transparency) 'indexed #f)
|
|
(error 'transparency-indexed-not-implemented)])]
|
|
[(hash-ref ($png-image png) 'hasAlphaChannel #f)
|
|
;; 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.]
|
|
(define-values (img-bytes alpha-bytes) (split-alpha-channel png))
|
|
(set-$png-img-data! png (deflate img-bytes))
|
|
(set-$png-alpha-channel! png (deflate alpha-bytes))]))
|
|
|
|
(when ($png-alpha-channel png)
|
|
(define sMask-ref
|
|
(make-ref
|
|
(mhash 'Type 'XObject
|
|
'Subtype 'Image
|
|
'Height ($img-height png)
|
|
'Width ($img-width png)
|
|
'BitsPerComponent 8
|
|
'Filter 'FlateDecode
|
|
'ColorSpace 'DeviceGray
|
|
'Decode '(0 1))))
|
|
(ref-write sMask-ref ($png-alpha-channel png))
|
|
(ref-end sMask-ref)
|
|
(dict-set! ($img-ref png) 'SMask sMask-ref))
|
|
|
|
;; embed the actual image data
|
|
(ref-write ($img-ref png) ($png-img-data png))
|
|
(ref-end ($img-ref png)))
|
|
|
|
(define (split-alpha-channel png)
|
|
(define ip ($img-data png))
|
|
(file-position ip 0)
|
|
(define bmap (read-bitmap ip 'png/alpha))
|
|
(define pixels (make-bytes (* 4 ($img-width png) ($img-height png))))
|
|
(send bmap get-argb-pixels 0 0 ($img-width png) ($img-height png) pixels)
|
|
(parameterize ([current-input-port (open-input-bytes pixels)])
|
|
(define argb-len (/ (bytes-length pixels) 4))
|
|
(define img-bytes (make-bytes (* argb-len 3)))
|
|
(define alpha-bytes (make-bytes argb-len))
|
|
(for ([argb-bytes (in-port (λ (p) (read-bytes 4 p)))]
|
|
[i (in-range argb-len)])
|
|
(bytes-copy! alpha-bytes i argb-bytes 0 1)
|
|
(bytes-copy! img-bytes (* i 3) argb-bytes 1 4))
|
|
(values img-bytes alpha-bytes)))
|
|
|
|
|
|
;; test files
|
|
;; http://www.libpng.org/pub/png/png-sitemap.html#images
|
|
(module+ test
|
|
(define pic (make-png (open-input-file "../ptest/assets/death-alpha.png")))
|
|
(define-values (img alpha) (split-alpha-channel pic)))
|
|
|
|
|
|
#|
|
|
Grab key chunks from PNG. Doesn't require heavy lifting from libpng.
|
|
|#
|
|
|
|
(define (read-png ip-or-bytes)
|
|
(define png (make-hasheq))
|
|
(parameterize ([current-input-port (if (input-port? ip-or-bytes)
|
|
ip-or-bytes
|
|
(open-input-bytes ip-or-bytes))])
|
|
(define header (read-bytes 8))
|
|
(let loop ()
|
|
(cond
|
|
[(eof-object? (peek-byte)) png]
|
|
[else
|
|
(define chunk-size (read-32bit-integer))
|
|
(define chunk-name (read-bytes 4))
|
|
(case chunk-name
|
|
[(#"IHDR") (hash-set*! png
|
|
'width (read-32bit-integer)
|
|
'height (read-32bit-integer)
|
|
'bits (read-byte)
|
|
'colorType (read-byte)
|
|
'compressionMethod (read-byte)
|
|
'filterMethod (read-byte)
|
|
'interlaceMethod (read-byte))]
|
|
[(#"PLTE") (hash-set*! png 'palette (read-bytes chunk-size))]
|
|
[(#"IDAT") (hash-set*! png 'imgData (read-bytes chunk-size))]
|
|
[(#"tRNS")
|
|
;; This chunk can only occur once and it must occur after the
|
|
;; PLTE chunk and before the IDAT chunk.
|
|
(define transparency (mhash))
|
|
(case (hash-ref png 'colorType (λ () (error 'read-png "PNG file is loco")))
|
|
[(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).
|
|
(hash-set! transparency 'indexed
|
|
(append (read-bytes chunk-size)
|
|
(make-list (min 0 (- 255 chunk-size)) 255)))]
|
|
[(0)
|
|
;; Greyscale. Corresponding to entries in the PLTE chunk.
|
|
;; Grey is two bytes, range 0 .. (2 ^ bit-depth) - 1]
|
|
(hash-set! transparency 'grayscale (bytes-ref (read-bytes chunk-size) 0))]
|
|
[(2)
|
|
;; True color with proper alpha channel.
|
|
(hash-set! transparency 'rgb (read-bytes chunk-size))])
|
|
(hash-set! png 'transparency transparency)]
|
|
[(#"tEXt")
|
|
(define text (read-bytes chunk-size))
|
|
#|
|
|
text = @read(chunkSize)
|
|
index = text.indexOf(0)
|
|
key = String.fromCharCode text.slice(0, index)...
|
|
@text[key] = String.fromCharCode text.slice(index + 1)...
|
|
|#
|
|
42]
|
|
[(#"IEND") (define color-value (case (hash-ref png 'colorType)
|
|
[(0 3 4) 1]
|
|
[(2 6) 3]))
|
|
(define alpha-value (and (member (hash-ref png 'colorType) '(4 6)) (hash-ref png 'colorType)))
|
|
(hash-set*! png
|
|
'colors color-value
|
|
'hasAlphaChannel alpha-value
|
|
'pixelBitlength (* (hash-ref png 'bits) (+ color-value (if alpha-value 1 0)))
|
|
'colorSpace (case color-value
|
|
[(1) "DeviceGray"]
|
|
[(3) "DeviceRGB"]))]
|
|
[else (read-bytes chunk-size)])
|
|
(read-bytes 4) ; skip crc
|
|
(loop)]))))
|
|
|
|
|
|
|
|
(define (read-32bit-integer)
|
|
(define signed #f) (define big-endian #t)
|
|
(integer-bytes->integer (read-bytes 4) signed big-endian))
|
|
|
|
(module+ test
|
|
(require rackunit)
|
|
(check-equal?
|
|
(read-png (open-input-file "../ptest/assets/test.png"))
|
|
(read-png (file->bytes "../ptest/assets/test.png")))) |