parameters of (setup)externalfigure, conversions etc.

[Henning Hraban Ramm via ntg-context <ntg-context@ntg.nl>]

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’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, crossreference
* resources
* display
* order
* crop, transform
* controls, preview: only related to video and thus obsolete?
* hfactor/wfactor: When do these make sense? (I know factor)

I accidentally learned that I can use parameters of \framed, but the 
inheritance from \setupframed is not explicit – some are mentioned, like 
backgroundcolor, others not, even if they work, like corner (but they 
don’t affect the image).


Hraban
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