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

Hans Hagen j.hagen at xs4all.nl
Sat Feb 23 12:48:31 CET 2019


On 2/23/2019 12:37 PM, Rudolf Bahr wrote:
> On Sat, Feb 23, 2019 at 11:56:32AM +0100, Hans Hagen wrote:
>> On 2/23/2019 11:08 AM, Rudolf Bahr wrote:
>>> 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
>>>
>>>                                                               picture-height-in-px
>>> asked-picture-height-in-pt = preset-picture-width-in-pt  *  --------------------
>>>                                                		    picture-width-in-px
>>>
>>> This is simple and normally it suffices for me.
>> Better use the built-in methods:
>>
>> \starttext
>>
>>      \getfiguredimensions[t:/sources/mill.png]
>>
>>      (\figurewidth,\figureheight)
>>
>>      (\figurexsize,\figureysize)
>>
>> \stoptext
>>
>> as it prevents opening the files multiple times. It's also more futureproof.
>>
>> Hans
>>
> 
> Hi Hans,
> 
> I fear it doesn't work. I used the above code with a test-picture of mine
> (in .png and .jpg version) and got:
> 
> (0sp,0sp)
> (0,0)
> 
> Now I'm baffled what the explanation could be. Are "mill" or "cow" somehow
> specially prepared? I used:
> 
> ConTeXt  ver: 2018.03.16 22:20 MKIV beta  fmt: 2018.3.21 and
> getfiguredimensions[~/my-test-picture.png]

maybe the image is not found ... what if you replace the ~



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