[NTG-context] Downsampling images (again)

[NTG-context] Downsampling images (again)

[Henning Hraban Ramm]

This is lying around for years, let’s try to get it finally working.
The code below works, but doesn’t do the right thing.

Since the original image doesn’t contain a resolution setting, gm 
doesn’t do anything:
“gm convert: image does not contain resolution”

It would be more reliable to use “gm convert -resize”, but for that we 
need to know the final pixel size.

How can a converter function access …
– the final (scaled) size of a placed image
– the original pixel size of an image
?
With that information it would be easy to calculate the target pixel size.

And then it would be nice to hook this function into 
\setupexternalfigure[conversion=]


"""
\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)
     logs.report("downsample", cmd)
     os.execute(cmd)
end

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

\setupexternalfigure[
   %conversion=downsampler,% not used
   resolution=10,
]

\starttext

\externalfigure[https://upload.wikimedia.org/wikipedia/commons/d/dd/Hermann_Zapf_signing.jpg][width=.5\textwidth]

\stoptext
"""

Hraban
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[NTG-context] Re: Downsampling images (again)

[Alan Braslau via ntg-context]

Hraban,

I would first "fix" my image sources, individually, to contain missing
resolution information.

Alan

On Sat, 21 Sep 2024 13:21:08 +0200
Henning Hraban Ramm <texml@fiee.net> wrote:

> This is lying around for years, let’s try to get it finally working.
> The code below works, but doesn’t do the right thing.
> 
> Since the original image doesn’t contain a resolution setting, gm 
> doesn’t do anything:
> “gm convert: image does not contain resolution”
> 
> It would be more reliable to use “gm convert -resize”, but for that
> we need to know the final pixel size.
> 
> How can a converter function access …
> – the final (scaled) size of a placed image
> – the original pixel size of an image
> ?
> With that information it would be easy to calculate the target pixel
> size.
> 
> And then it would be nice to hook this function into 
> \setupexternalfigure[conversion=]
> 
> 
> """
> \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)
>      logs.report("downsample", cmd)
>      os.execute(cmd)
> end
> 
> -- Set the PDF and default JPEG converters to the above function.
> figures.converters.jpg.pdf = downsampler
> figures.converters.jpg.default = downsampler
> \stopluacode
> 
> \setupexternalfigure[
>    %conversion=downsampler,% not used
>    resolution=10,
> ]
> 
> \starttext
> 
> \externalfigure[https://upload.wikimedia.org/wikipedia/commons/d/dd/Hermann_Zapf_signing.jpg][width=.5\textwidth]
> 
> \stoptext
> """
> 
> Hraban
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an
> entry to the Wiki!
> 
> maillist : ntg-context@ntg.nl
> / https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nl webpage  : https://www.pragma-ade.nl / https://context.aanhet.net (mirror)
> archive  : https://github.com/contextgarden/context
> wiki     : https://wiki.contextgarden.net
> ___________________________________________________________________________________
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

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___________________________________________________________________________________

[NTG-context] Re: Downsampling images (again)

[Henning Hraban Ramm]

Am 21.09.24 um 16:30 schrieb Alan Braslau:
> I would first "fix" my image sources, individually, to contain missing
> resolution information.

The resolution setting is just metadata, it doesn’t affect pixel or file 
size. I need a function that works with “real” (pixel) sizes of images.

Hraban
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___________________________________________________________________________________

[NTG-context] Re: Downsampling images (again)

[Peter Münster]

[-- Attachment #1: Type: text/plain, Size: 310 bytes --]

On Sat, Sep 21 2024, Henning Hraban Ramm wrote:

> How can a converter function access …
> – the final (scaled) size of a placed image

Hi,

I use "figures.current().request" in my module (here attached).


> – the original pixel size of an image ?

I use img.scan() for that.

HTH,
-- 
           Peter

[-- Attachment #2: grph-downsample.lua --]
[-- Type: application/octet-stream, Size: 1610 bytes --]

if not modules then modules = { } end modules ['grph-downsample'] = {
  version   = 1.001,
  comment   = "companion to grph-inc.mkiv",
  author    = "Peter Münster",
  copyright = "PRAGMA ADE / ConTeXt Development Team",
  license   = "see context related readme files"
}

local format = string.format
-- figures.cachepaths.path = "cache" -- should be setup-option
local function sample_down(oldname, newname, resolution)
    local request = figures.current().request
    local width = request.width
    local height = request.height
    if resolution == "" or (not width and not height) then
        print(format("Nothing to do: %s, %s, %s", oldname, newname, resolution))
        return
    end
    local inch = 72.27
    local image = img.scan{filename = oldname}
    local xy = image.xsize / image.ysize
    if not width then
        width = height * xy / 65536
    end
    if not height then
        height = width / xy / 65536
    end
    local xsize = resolution * width / inch
    local ysize = resolution * height / inch
    if xsize < image.xsize or ysize < image.ysize then
        local s = format("gm convert -resize %dx%d %s %s",
                         xsize, ysize, oldname, newname)
        print("Conversion: " .. s)
        os.execute(s)
    else
        print(format("Nothing to do: %s, %s, %s", oldname, newname, resolution))
        print(format("xsize = %d, ysize = %d", xsize, ysize))
    end
end

local formats = {"png", "jpg", "gif"}

for _, s in ipairs(formats) do
    figures.converters[s] = figures.converters[s] or {}
    figures.converters[s]["lowres." .. s] = sample_down
end

[-- Attachment #3: Type: text/plain, Size: 511 bytes --]

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___________________________________________________________________________________

[NTG-context] Re: Downsampling images (again)

[Alan Braslau via ntg-context]

On Sat, 21 Sep 2024 21:44:53 +0200
Henning Hraban Ramm <texml@fiee.net> wrote:

> Am 21.09.24 um 16:30 schrieb Alan Braslau:
> > I would first "fix" my image sources, individually, to contain
> > missing resolution information.  
> 
> The resolution setting is just metadata, it doesn’t affect pixel or
> file size. I need a function that works with “real” (pixel) sizes of
> images.

Exactly. The raw data is just pixels, and metadata sets what the
expected pixel size might be. Of course, this metadata can be
meaningless as the user can and often does rescale the image to meet
the typesetting needs.

The image manipulation tools use this metadata to resample resolution.
I found this very useful as I used *hundreds* of scanned X-ray images
that had real sizes, high resolution and 16 or even 24 bit depth. Of
course, I had to reduce all of this in order to include them in a
digestible and printable pdf.

Alan
___________________________________________________________________________________
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