---

Utilities

Other Guile-CV utility procedures, methods and variables.

Procedures

im-display

im-display-channel

im-show

Variables

%image-cache

%image-cache-format

Procedures

Procedure: im-display image [#:proc #f] [#:port (current-output-port)] ¶

Procedure: im-display-channel channel width height [#:proc #f] [#:port (current-output-port)] ¶

Returns nothing.

Displays the content of image or channel on port.

The optional #:proc keyword argument must either be #f, the default, or a procedure that accepts a single (32 bits float) argument. When #:proc is #f, im-display will use an internally defined procedure which formats its argument ‘à la octave’: nine positions, six decimals, all number aligned on the dot. any value >= 1000 is converted to use the exponential float notation. Here is an ‘hand made’ example:

...
$2 = (4 3 3 (#f32(0.0 1.0 2.0 3.0 4.0 5.0) ... ...)
scheme@(guile-user)> (im-divide $2 99)
$3 = (4 3 3 (#f32(10.1010103225708 0.010101010091602802 …) …))
scheme@(guile-user)> (im-set! $3 0 0 0 10000)
$4 = (4 3 3 (#f32(10000.0 0.010101010091602802 # # # # …) …))
scheme@(guile-user)> (im-display $4)
-|

Channel 1

     1.0E+4    0.01010    0.02020    0.03030
    0.04040    0.05051    0.06061    0.07071
    0.08081    0.09091    0.10101    0.11111

Channel 2

    0.12121    0.13131    0.14141    0.15152
    0.16162    0.17172    0.18182    0.19192
    0.20202    0.21212    0.22222    0.23232

Channel 3

    0.24242    0.25253    0.26263    0.27273
    0.28283    0.29293    0.30303    0.31313
    0.32323    0.33333    0.34343    0.35354

Caution: unless you specify port, both this and im-display-channel procedures are meant to be used on very small and testing images, otherwise even on a small image, it might be ok in a terminal, but it will definitely will kill your emacs.

Method: im-show filename ¶

Method: im-show image [scale #f] ¶

Method: im-show image name [scale #f] ¶

Returns the string "#<Image: …>", where "…" is either filename or a filename constructed by im-show, see below.

The optional scale argument can take the following values:

#f

pixel values are ‘clipped’: values < 0 are saved as 0, values > 255 are saved as 255, and otherwise are saved unchanged

#t

all pixel values are scaled²⁹ to the [0 255] range

These three methods will also effectively dislay the image if you are using Geiser, which analyzes Guile’s procedures and methods returned values (through the use of its pattern matcher), and when appropriate, triggers its image display mechanism.

Geiser has two variables that allow you to choose either to inline images in its Emacs (Guile repl) buffer, or to display them using externel viewer: geiser-image-viewer and geiser-repl-inline-images-p. You may choose to add these variables in your .emacs file, for example:

(setq geiser-image-viewer "eog")
(setq geiser-repl-inline-images-p nil)

Note that (setq geiser-repl-inline-images-p t) will only work if you are using a graphics-aware Emacs, and otherwise, will fall on the external viewer approach, if the variable geiser-image-viewer has been defined. When using Geiser in a non graphics-aware Emac, or when using the external viewer approach, images will appear as buttons: press return on them to invoke (or raise) the external viewer (window containing that image).

Except for the first im-show method, Guile-CV has to save the image first, and does it in the location defined by the %image-cache variable. If you call im-show passing name, the image is saved as %image-cache/name.png, otherwise under a generated name, the result of (symbol->string (gensym "im-show-")).

Note that if you do not specify name, a new external viewer window is opened at each im-show invocation, even for identical image calls: this because in Guile-CV, on purpose, images are just list, with no (unique) identifier, and there is no way for im-show to know ... Further to this point, when you pass name as an argument, you are not ‘identifying’ image, which may actually differ, but rather just ask to reuse the filename and hence the external viewer window associated with it.

Last note: many external viewers, such as Eog (the Gnome Eye Viewer), will try to apply, per default, some sort of smoothing techniques, especially on zoom-in and zoom-out: where this is fine for viewing ‘lazer’ pictures, you probably want to check and disable these options when working with Guile-CV.

Variables

Variable: %image-cache ¶

Specifies the location used by im-show to save images.

The default value is /tmp/<username>/guile-cv, but you may set! it. If you’d like to reuse that location for future guile-cv sessions, you may save it in guile-cv’s ‘per user’ config file <userdir>/.config/guile-cv as an assoc pair, here is an example:

cat ~/.config/guile-cv.conf
((image-cache . "~/tmp"))

Note that if used, the ‘~’ is expanded at load time, so in geiser, it becomes:

scheme@(guile-user)> ,use (cv)
scheme@(guile-user)> %image-cache
-|
$2 = "/home/david/tmp"

Variable: %image-cache-format ¶

Specifies the format used by im-show to save images.

The default value is "png", but you may set! it. If you’d like to reuse that format for future guile-cv sessions, you may save it in guile-cv’s ‘per user’ config file <userdir>/.config/guile-cv, as an assoc pair, here is an example:

cat ~/.config/guile-cv.conf
((image-cache-format . "jpg"))