Am 11.08.22 um 15:51 schrieb Henning Hraban Ramm via ntg-context:
Hi Hans,
yesterday you told me about the image conversions in grph-con.lua, and I
tried to find out how to use them. Up to know I only knew "mp" for SVG
images.
I found I can use "gray.pdf" or "cmyk.pdf" to convert an image (JPG or
PNG) to grayscale/CMYK, but the resolution isn’t used for downsampling
(of course, it’s not mentioned in the command template):
\externalfigure[hacker][conversion={gray.pdf},resolution=72]
I tried to write my own downsampling converter, but don’t understand how
I can hook it into the list of converters:
"""
local downsample = sandbox.registerrunner {
name = "downsample",
program = "gm",
template = [[convert -compress Zip -sampling-factor 1x1 -density
%resolution%x%resolution% -resample %resolution%x%resolution% %oldname%
%newname%]],
checkers = checkers,
defaults = defaults,
}
programs.downsample = { runner = downsample }
I found the solution in
https://wiki.contextgarden.net/Using_Graphics#Image_Conversion, but
that’s not as elegant as those in grph-inc.lua
(And I learned that ImageMagick’s convert works differently than
GraphicsMagick’s WRT -density; i.e. you must use "gm convert".)
Peter Münster’s grph-downsample.lua was better, it calculated the actual
pixel size necessary, but that doesn’t work any more.
"""
(I’m not sure if I must calculate the desired pixel size beforehand.)
-*-*-
Apart from converters, there are several parameters of \externalfigure
that I don’t understand and thus can’t document in the Wiki; a few are
even not yet documented in the interface files:
* equalwidth/equalheight
* s/sx/sy
* xmax/ymax
* prefix, label, comment
* bodyfont
* mask
* frames (≠ frame)
* interaction (PDF inclusion; found)crossreference
* resources
* display (alternative source? multimedia only?)
* order (of extensions; found)
* crop, transform
* controls, preview: only related to video and thus obsolete?
* hfactor/wfactor: When do these make sense? (I know factor)
Also, orientation seems to be missing in the interface (auto-syntax
doesn’t pick it up).
Hraban
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