98 lines
3.3 KiB
Plaintext
98 lines
3.3 KiB
Plaintext
sunterlib/scsh/image-info -- Extracting Vital Stats from Images
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Loose port of small parts from Marco Schmidt's public domain ImageInfo 1.3
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Java program. The port supports gif, jpeg, png images and extracts
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* the width and height in pixels,
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* maybe the physical width and height in dpi,
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* the (unreliable) colour depth (#bits / pixel),
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* a symbolic format id: GIF87A, GIF89A, JPEG, PNG.
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All numbers are integers. The colour depth may deviate from the actual
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value in multi-part gifs. (It is taken from the global header, but
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local palettes may reset, typically increase, that value.)
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The original code, which does much more, is at
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http://www.geocities.com/marcoschmidt.geo/image-info.html
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Typical use: in web-authoring, generate the width and height tags of
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inline images programmatically, like so:
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;; ,open image-info
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(receive (w h) (with-input-from-file "pix/herb.jpg"
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(lambda () (image-dimension (current-input-port))))
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`(img ((src "pix/herb.jpg")
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(width ,w) (height ,h)
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(alt "Enter!"))))
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--> (img ((src "pix/herb.jpg") (width 632) (height 474) (alt "Enter!")))
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*
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Procedures
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exported by structure IMAGE-INFO. IMAGE-DIMENSION is the convenient
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user interface for the most common usage: getting pixel width and
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height. Some procedures refer to ``b.s.''s. These are described at
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bottom.
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(image-dimension img) --> [w h]
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Synopsis: Extract the (numeric) width W and height H (in pixels) from
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the byte source (input port, file descriptor, byte-vector, b.s.(*))
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IMG -- or signal an error.
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*
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(get-image-info bs) --> info | #f
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Synopsis: Extract information on the image represented by b.s.(*) BS
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and return an image-info record or #f. (Don't believe in the colour
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depth for gifs.)
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*
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(image:info-format info) --> format | #f
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Get the symbolic format id from image-info record INFO.
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(image:info-depth info) --> depth | #f
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Get the colour DEPTH (#bits/pixel) from image-info record INFO.
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(image:info-width/pixel info) --> w | #f
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(image:info-height/pixel info) --> h | #f
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Get the pixel width W resp. height H from image-info record INFO.
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(image:info-width/dpi info) --> width | #f
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(image:info-height/dpi info) --> height | #f
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Get the physical width W resp. height H in dots per inch from INFO.
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*
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(*) Creating and accessing ``byte streams''
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Byte-streams, or b.s.s for short, are random-access lazy byte sources.
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The image-info project doesn't commit to the current implementation,
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i.e. create and access b.s.s by the procedures below or blame yourself.
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(inport->byte-stream in) --> bs
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Synopsis: Convert the input port (or file descriptor) IN to a
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b.s. BS. (The BS will read from IN as needed. It doesn't duplicate
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or close IN.)
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*
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(byte-vector->byte-stream bv) --> bs
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Synopsis: Convert the byte-vector bv to a b.s. BS.
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*
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(segment-byte-stream bs start end) --> [bv bs']
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Synopsis: Segment the b.s. BS into the first [start:end) bytes in the
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byte-vector BV and the following [end:*) bytes in the b.s. BS', or get
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the little that's there up to eof. BV may be short, BV and BS' may be
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empty.
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oOo
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