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.
typesetting/pitfall/pitfall/jpeg-structy.rkt

74 lines
2.6 KiB
Racket

#lang debug racket/base
(require
"core.rkt"
"reference.rkt"
racket/class
racket/contract
racket/dict
sugar/unstable/class
sugar/unstable/js
sugar/unstable/dict
sugar/unstable/port)
(provide +JPEG (struct-out JPEG))
(define MARKERS '(#xffc0 #xffc1 #xffc2 #xffc3 #xffc5 #xffc6 #xffc7
#xffc8 #xffc9 #xffca #xffcb #xffcc #xffcd #xffce #xffcf))
(define (read-16bit-integer [port (current-input-port)])
(define signed #f) (define big-endian #t)
(integer-bytes->integer
(read-bytes 2 port) signed big-endian))
(struct JPEG image (data bits channels colorSpace) #:transparent #:mutable)
(define (+JPEG data [label #f])
(parameterize ([current-input-port (if (input-port? data) data (open-input-bytes data))])
(unless (equal? (read-16bit-integer) #xffd8)
(error 'JPEG "Start of Input marker byte not found"))
(define marker (let loop ([skip 0])
(read-bytes skip)
(define m (read-16bit-integer))
(if (memv m MARKERS)
m
(loop (read-16bit-integer (open-input-bytes (peek-bytes 2 0)))))))
(read-16bit-integer) ; what is it and why am I ignoring it?
(define bits (read-byte))
(define height (read-16bit-integer))
(define width (read-16bit-integer))
(define channels (read-byte))
(define colorSpace (case channels
[(1) "DeviceGray"]
[(3) "DeviceRGB"]
[(4) "DeviceCMYK"]))
(define obj #f)
(JPEG label width height obj data bits channels colorSpace)))
(define (embed this)
#;(object? . ->m . void?)
(unless (· this obj)
(set-field! obj this
(make-ref
(mhash
'Type "XObject"
'Subtype "Image"
'BitsPerComponent (· this bits)
'Width (· this width)
'Height (· this height)
'ColorSpace (· this colorSpace)
'Filter "DCTDecode")))
;; add extra decode params for CMYK images. By swapping the
;; min and max values from the default, we invert the colors. See
;; section 4.8.4 of the spec.
(when (equal? (· this colorSpace) "DeviceCMYK")
(dict-set! (· this obj) 'Decode '(1.0 0.0 1.0 0.0 1.0 0.0 1.0 0.0)))
(port-position (· this data) 0)
(send (· this obj) end (· this data))))
(module+ test
(require rackunit)
(check-equal? (number->string (read-16bit-integer (open-input-bytes (bytes #x12 #x34 #x56))) 16) "1234")
(+JPEG (open-input-file "../ptest/assets/test.jpeg")))