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