Hi Julian,
I had the same question a couple of days ago and I found a thread on the
mailing list, which I'm reposting here. Although this worked for me, I found
downsampling of the pdf with gs more convenient.
Hope this helps,
Benjamin
%%%%%
if not modules then modules = { } end modules ['grph-downsample'] = {
version = 1.101,
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"
}
assert(not figures.getinfo2)
figures.getinfo2 = function(name, page) -- [ [NTG-context] Pdf info with
Lua/Ctx API ]
if type(name) == "string" then
name = { name = name, page = page }
end
if name.name then
local data = figures.push(name)
local info = figures.identify()
if info.status.status ~= 0 then
figures.check() -- !Counts pages here!
end
figures.pop()
return --data
info
end
end
local format = string.format
-- figures.cachepaths.path = "cache" -- should be setup-option
local function sample_down(oldname, newname, resolution)
print("DOWNSAMPLE sample_down " .. oldname .. " to " .. newname)
local request = figures.current().request
local width = request.width
local height = request.height
if resolution == "" then -- or (not width and not height) then
print(format("DOWNSAMPLE Nothing to do: %s, %s, %s dpi, %s x %s px",
oldname, newname, resolution, width, height))
return
end
local TEXpt = 65536
local inch = 72.27
-- MkIV:
-- local image = img.scan{filename = oldname}
-- LMTX:
local image = figures.getinfo(oldname,1)
image = image.status.private
local xy = image.xsize / image.ysize
if (not width and not height) then
-- no size requested? use default width
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)
print(format("DOWNSAMPLE image size %dx%dpx. requested %dx%d?", image.xsize,
image.ysize, width, height))
local xsize = math.floor(resolution * width / inch)
local ysize = math.floor(resolution * height / inch)
print(format("DOWNSAMPLE size %d x %d to %d x %d", image.xsize, image.ysize,
xsize, ysize))
if xsize < image.xsize or ysize < image.ysize then
local s = format("gm convert -resize %dx%d -resample %dx%d \"%s\" \"%s\"",
xsize, ysize, resolution, resolution, oldname, newname)
print("DOWNSAMPLE Conversion: " .. s)
os.execute(s)
else
print(format("DOWNSAMPLE Nothing to do: %s, %s, %s dpi, %d x %d px",
oldname, newname, resolution, width, height))
print(format("DOWNSAMPLE 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
local function sample_down_pdf(oldname, newname, resolution)
print("DOWNSAMPLE sample_down " .. oldname .. " to " .. newname)
-- MkIV:
-- local image = img.scan{filename = oldname}
-- LMTX:
local image = figures.getinfo(oldname,1)
image = image.status.private
local s = format("gs \
-o \"%s\" \
-sDEVICE=pdfwrite \
-dDownsampleColorImages=true \
-dDownsampleGrayImages=true \
-dDownsampleMonoImages=true \
-dColorImageResolution=%s \
-dGrayImageResolution=%s \
-dMonoImageResolution=%s \
-dColorImageDownsampleThreshold=1.0 \
-dGrayImageDownsampleThreshold=1.0 \
-dMonoImageDownsampleThreshold=1.0 \
\"%s\"",
oldname, resolution, resolution, resolution, newname)
print("DOWNSAMPLE Conversion: " .. s)
os.execute(s)
end
figures.converters["pdf"]["lowres." .. "pdf"] = sample_down_pdf
%%%%%
\loadluafile[grph-downsample]
\doifmodeelse{print}{%
\def\Resolution{300}
}{%
\def\Resolution{96}
}%
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