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77 lines
2.7 KiB
Racket
77 lines
2.7 KiB
Racket
#lang debug racket/base
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(require
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racket/class
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racket/match
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"reference.rkt"
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racket/dict
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sugar/unstable/dict)
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#|
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https://github.com/mbutterick/pdfkit/blob/master/lib/image/jpeg.coffee
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|#
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(provide JPEG)
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(define MARKERS '(#xffc0 #xffc1 #xffc2 #xffc3
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#xffc5 #xffc6 #xffc7
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#xffc8 #xffc9 #xffca #xffcb
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#xffcc #xffcd #xffce #xffcf))
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(define JPEG
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(class object%
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(super-new)
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(init-field [(@data data)] [(@label label) #f])
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(define jpeg-ip (if (input-port? @data) @data (open-input-bytes @data)))
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(unless (= (read-16bit-integer jpeg-ip) #xffd8)
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(error 'JPEG "Start of input marker byte not found"))
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(define marker (let loop ([skip 0])
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(read-bytes skip jpeg-ip)
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(define m (read-16bit-integer jpeg-ip))
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(if (memv m MARKERS)
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m
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(loop (read-16bit-integer (peek-bytes 2 0 jpeg-ip))))))
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(read-16bit-integer jpeg-ip)
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(field [(@bits bits) (read-byte jpeg-ip)]
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[(@height height) (read-16bit-integer jpeg-ip)]
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[(@width width) (read-16bit-integer jpeg-ip)]
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[(@channels channels) (read-byte jpeg-ip)]
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[(@colorSpace colorSpace) (case @channels
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[(1) 'DeviceGray]
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[(3) 'DeviceRGB]
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[(4) 'DeviceCMYK])]
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[(@obj obj) #f])
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(define/public (embed)
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(unless @obj
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(set! @obj (make-ref
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(mhash
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'Type 'XObject
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'Subtype 'Image
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'BitsPerComponent @bits
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'Width @width
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'Height @height
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'ColorSpace @colorSpace
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'Filter 'DCTDecode)))
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;; add extra decode params for CMYK images. By swapping the
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;; min and max values from the default, we invert the colors. See
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;; section 4.8.4 of the spec.
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(when (eq? @colorSpace 'DeviceCMYK)
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(dict-set! @obj 'Decode '(1.0 0.0 1.0 0.0 1.0 0.0 1.0 0.0)))
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(file-position @data 0)
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(ref-write @obj @data)
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(ref-end @obj)))))
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(define (read-16bit-integer ip-or-bytes)
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(define signed #f) (define big-endian #t)
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(integer-bytes->integer (read-bytes 2 (match ip-or-bytes
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[(? bytes? bs) (open-input-bytes bs)]
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[ip ip])) signed big-endian))
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(module+ test
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(require rackunit)
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(check-equal? (number->string (read-16bit-integer (bytes #x12 #x34 #x56)) 16) "1234")
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(make-object JPEG (open-input-file "../ptest/assets/test.jpeg"))) |