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

["Peter Münster" <pm@a16n.net>]

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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 --]
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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

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