if not modules then modules = { } end modules ['grph-downsample'] = {
  version   = 1.103,
  comment   = "companion to grph-inc.mkiv",
  author    = "Peter Münster", -- adapted to LMTX by Hraban
  copyright = "PRAGMA ADE / ConTeXt Development Team",
  license   = "see context related readme files"
}

local format = string.format
local report = logs.reporter("DOWNSAMPLE")
local function sample_down(oldname, newname, resolution)
  report("sample_down %s to %s (%s)", oldname, newname, resolution)
  local request = figures.current().request
  -- this is probably the original pixel size
  local width = request.width
  local height = request.height
  -- width/height are integer in sp or a boolean
  local TEXpt = 65536
  local inch = 72.27
  if resolution == "" then -- or (not width and not height) then
    report("Nothing to do (missing resolution): %s, %s, %s dpi, %s x %s px", oldname, newname, resolution, width, height)
    return
  else
    report("Requested: %s, %s, %s dpi, %s x %s px", oldname, newname, resolution, width, height)
  end

  -- MkIV:
  -- local image = img.scan{filename = oldname}

  -- LMTX:
  local image = figures.getinfo(oldname,1)
  image = image.status.private

  local xy = image.xsize / image.ysize -- size ratio
  if (not width and not height) then
    -- no size requested? use default width
    -- probably wrong…
    width = 300 * TEXpt
  end
  if not width then
    height = height / TEXpt
    width = height * xy
  end
  if not height then
    width = width / TEXpt
    height = width / xy
  end
  width = math.floor(width)
  height = math.floor(height)
  report("image size %dx%dpx. requested %dx%dpt at %ddpi.", image.xsize, image.ysize, width, height, resolution)
  local xsize = math.floor(resolution * width / inch)
  local ysize = math.floor(resolution * height / inch)
  report("resize %dx%dpx to %dx%dpx:", image.xsize, image.ysize, xsize, ysize)
  if xsize < image.xsize or ysize < image.ysize then
    -- maybe add a tolerance of 20% (don’t downsample if the difference is marginal)
    local s = format("gm convert -resize %dx%d -resample %dx%d \"%s\" \"%s\"",
                     xsize, ysize, resolution, resolution, oldname, newname)
    report("calling: %s", s)
    os.execute(s)
  else
    report("Nothing to do (image smaller than requested): %s, %s, %s dpi, %d x %d px", oldname, newname, resolution, width, height)
    report("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 {}
  -- use \setupexternalfigure[conversion=lowres.jpg]:
  figures.converters[s]["lowres." .. s] = sample_down
  -- use without setup:
  --figures.converters[s].default = sample_down
  --figures.converters[s].pdf = sample_down -- gets used
end