[NTG-context] When newsizing an external figure bei [width=<some pt>], what will be its height in pt and viceversa?

Rudolf Bahr quasi at quasi.de
Sat Feb 23 11:08:18 CET 2019

On Fri, Feb 22, 2019 at 12:59:55PM +0100, Peter M√ľnster wrote:
> On Fri, Feb 22 2019, Rudolf Bahr wrote:
> > The picture sizes in px One gets by invoking for instance graphics Magick's identify
> > in a lua program:
> Or just img.scan():
> \startluacode
>   local image = img.scan{filename = "my-image.jpg"}
>   logs.report("xsize", image.xsize)
>   logs.report("ysize", image.ysize)
> \stopluacode
> -- 
>            Peter

Hi Peter,

thank you for pointing to img.scan{}! It's indeed shorter than to invoke Graphics Magick
in Lua. Remains the conversion of image sizes into pt. There is an example in the chapter
"Calculations in Lua" in "https://wiki.contextgarden.net/Image_Placement" (a work in
progress). According to there it's necessary to know the resolution in order to convert
image sizes from px to pt which at least I don't know. Mostly I can preset one size of
a picture (say the width in pt) to be able to place it on a page and assuming
x-resolution = y-resolution and keeping width-to-height ratio I calculate the missing
size (here the height in pt) in Lua by

asked-picture-height-in-pt = preset-picture-width-in-pt  *  --------------------

This is simple and normally it suffices for me.


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