access image properties in Lua

access image properties in Lua

[Henning Hraban Ramm]

What’s the current approved way to get image properties within a Lua 
function?

very old:
local pic = figures.getinfo(figures.current().status.fullname)

used to work in 2019:
local pic = img.scan{filename = figures.current().status.fullname}

if I understand this right, "img" isn’t valid anymore:
"""
token call, execute: grph-imagelib.lua:37: attempt to index a nil value 
(global 'img')
"""

I’d like to know the pixel size and if possible also the scaled target 
size of an image; either the "current" one or by name.


Hraban
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Re: access image properties in Lua

[Hans Hagen]

On 7/11/2023 2:22 PM, Henning Hraban Ramm wrote:
> What’s the current approved way to get image properties within a Lua 
> function?
> 
> very old:
> local pic = figures.getinfo(figures.current().status.fullname)
> 
> used to work in 2019:
> local pic = img.scan{filename = figures.current().status.fullname}
> 
> if I understand this right, "img" isn’t valid anymore:
> """
> token call, execute: grph-imagelib.lua:37: attempt to index a nil value 
> (global 'img')
> """
> 
> I’d like to know the pixel size and if possible also the scaled target 
> size of an image; either the "current" one or by name.
\ctxlua{inspect(figures.getinfo("t:/sources/mill.png").used)}

\ctxlua{inspect(figures.getinfo("t:/sources/mill.png").status)}

etc .. no more faking the img lib

Hans

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[NTG-context] Re: access image properties in Lua

[Alan Braslau via ntg-context]

On 13/07/23 13/07/23, 09:19, Hans Hagen wrote:
> On 7/11/2023 2:22 PM, Henning Hraban Ramm wrote:
>> What’s the current approved way to get image properties within a Lua 
>> function?
>>
>> very old:
>> local pic = figures.getinfo(figures.current().status.fullname)
>>
>> used to work in 2019:
>> local pic = img.scan{filename = figures.current().status.fullname}
>>
>> if I understand this right, "img" isn’t valid anymore:
>> """
>> token call, execute: grph-imagelib.lua:37: attempt to index a nil 
>> value (global 'img')
>> """
>>
>> I’d like to know the pixel size and if possible also the scaled target 
>> size of an image; either the "current" one or by name.
> \ctxlua{inspect(figures.getinfo("t:/sources/mill.png").used)}
> 
> \ctxlua{inspect(figures.getinfo("t:/sources/mill.png").status)}
> 
> etc .. no more faking the img lib
> 
> Hans

Hraban, Hans, and mailing list.

This is interesting. I would find it useful to be able to report these 
properties though a tracker - should be fairly easy if not already 
available.

One works with images having a certain resolution, whatever that may be. 
We also might have a target resolution, say 300 dpi or perhaps better 
for printing. As the images are typically resized when used, the 
resulting resolutions might be anything. Optimizing the resolutions of 
the source images can result in optimal PDF sizes, i.e. not too high nor 
too low resolution.

I can even imagine an automated workflow where high-resolution, say 2400 
dpi or even greater bitmap images, are supplied and the included bitmap 
could be "resampled" resulting in the inclusion of a targeted 
resolution. However, the reporting of the included, likely resized image 
resolutions then used to adjust or resample the source files externally 
and manually case-by-case would be sufficient.

Any suggestions on how to hook-in such reporting?

Bonus question: how also to handle the case of
\startMPcode
draw figure "MyFigure" xsized TextWidth ;
...
\stopMPcode

--
Alan
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[NTG-context] Re: access image properties in Lua

[Henning Hraban Ramm]

Am 17.07.23 um 15:44 schrieb Alan Braslau via ntg-context:
> On 13/07/23 13/07/23, 09:19, Hans Hagen wrote:
>> On 7/11/2023 2:22 PM, Henning Hraban Ramm wrote:
>>> What’s the current approved way to get image properties within a Lua 
>>> function?

>>> I’d like to know the pixel size and if possible also the scaled 
>>> target size of an image; either the "current" one or by name.

>> \ctxlua{inspect(figures.getinfo("t:/sources/mill.png").used)}
>>
>> \ctxlua{inspect(figures.getinfo("t:/sources/mill.png").status)}
>>
>> etc .. no more faking the img lib

Thank you!

> We also might have a target resolution, say 300 dpi or perhaps better for printing.

What raster widths are you printing with?

More than 300 dpi would be only needed for very high resolution art 
prints with very fine details, possibly in FM raster.

Usually, 200 dpi final resolution is enough – 300 dpi are suggested to 
allow for some scaling.

For fine line art (black or spot color only, no rastering), 1200 dpi is 
suggested.

> I can even imagine an automated workflow where high-resolution, say 2400 
> dpi or even greater bitmap images, are supplied and the included bitmap 
> could be "resampled" resulting in the inclusion of a targeted 
> resolution. However, the reporting of the included, likely resized image 
> resolutions then used to adjust or resample the source files externally 
> and manually case-by-case would be sufficient.

Well, I was working for years with adapted versions of Peter Münster’s 
graph-downsample.lua.


You can hook in custom functions like this:

"""
\startluacode

local function downsampler(oldname, newname, resolution)
     if not resolution or resolution == "" then
         resolution = 72
     end
     local cmd = string.format(
       [[gm convert -resample %ix%i %s %s]],
       resolution, resolution, oldname, newname)
     --print(cmd)
     os.execute(cmd)
end
-- Beware: the calculation is still wrong,
-- I need to try figures.getinfo

-- Set the PDF and default JPEG converters to the above function.
--figures.converters.jpg.downsampler = downsampler
figures.converters.jpg.pdf = downsampler
figures.converters.jpg.default = downsampler

\stopluacode

\setupexternalfigure[
   conversion=downsampler,
   resolution=200,
]

"""

> Any suggestions on how to hook-in such reporting?

local report = logs.reporter("alan.imaging")

report("Now calculating...")

> Bonus question: how also to handle the case of
> \startMPcode
> draw figure "MyFigure" xsized TextWidth ;
> ...
> \stopMPcode

Is MyFigure a pixel image?
You could use \externalfigure within MP code.

Hraban

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[NTG-context] Re: access image properties in Lua

[Alan Braslau via ntg-context]

On 17/07/23 17/07/23, 18:20, Henning Hraban Ramm wrote:
>> Bonus question: how also to handle the case of
>> \startMPcode
>> draw figure "MyFigure" xsized TextWidth ;
>> ...
>> \stopMPcode
> 
> Is MyFigure a pixel image?
> You could use \externalfigure within MP code.

The MP operator figure calls \externalfigure.
However, the resolution downsampler hooked into externalfigure as you 
suggest would not give the desired resolutions once resized in MP.

A solution might be to use
draw rawtextext("\externalfigure[MyFigure][width=\textwidth") ;
which is OK for this simplified example but would not work when more 
sophisticated MetaPost transformations might be needed.



Along the lines of the conversion downsampler, a resolution reporter and 
manual resampling could be more efficient than reconverting the bitmap 
image at every run, of which there can be many.

--
Alan
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[NTG-context] Re: access image properties in Lua

[Henning Hraban Ramm]

(I assume you didn’t reply privately on purpose and take this back to 
the mailing list.)

Am 18.07.23 um 12:47 schrieb Alan Braslau:
> P.S. I have not used the built-in resolution= image conversion (using 
> gm/ImageMagik). I imagine that ConTeXt is clever enough to store the 
> converted file so that it only need to be converted once. However, is 
> the resolution resampled before or after size conversion in 
> \externalfigure?

If Hans didn’t add it recently, there‘s no automatical downsampling in 
ConTeXt (yet), that’s why I want to do this; the resolution parameter is 
apparently never used.

Hraban
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