TEXpt = 65536 -- sp per pt
TEXptpi = 72.27 -- pt per inch

function sp2mm(n)
	-- convert sp into mm
	return math.floor(n * 35.28 / TEXpt)/100
end

function glue2num(glue)
	-- convert TeX glue (e.g. skips) into dimensions(? or numbers)
	return glue.width + (glue.stretch * glue.stretch_order) - (glue.shrink * glue.shrink_order)
end

function getRegImgHeight(position, resolution, targetwidth)
	-- position (top/bottom), target resolution [dpi], target width [sp]
  local pic = img.scan{filename = figures.current().status.fullname}
	--local pic = figures.getinfo(figures.current().status.fullname)
	local picH = pic.ysize * TEXptpi * TEXpt / resolution  -- picture height in sp
	local picW = pic.xsize * TEXptpi * TEXpt / resolution  -- picture width in sp
  local bleed = tex.getdimen("Bleed")
	local lineH = tex.getdimen("lineheight")
	local scaling = targetwidth / picW  -- scaling factor
	picH = picH * scaling  -- scaled image height
  local nettoPicHeight = picH

  if position == "bottom" then
    local bottomOffset = bleed + tex.getdimen("bottomheight") + tex.getdimen("bottomdistance") + tex.getdimen("footerheight") + tex.getdimen("footerdistance")

    nettoPicHeight = picH - bottomOffset
    -- image height minus everything below the last line
  else -- position "top" or whatever
    local topOffset = bleed + tex.getdimen("topspace") + tex.getdimen("headerheight") + tex.getdimen("headerdistance") + tex.getdimen("topdistance")

  	local topskip = glue2num(tex.topskip)

    nettoPicHeight = picH - topOffset - topskip
    -- image height minus everything above the first line
  end

  local cutY = math.floor(nettoPicHeight) % math.floor(lineH)
  --  space to cut away (what exceeds the line grid)
	context((picH - cutY) .. "sp") -- final image height
end