-- stripping file ending from name

doc_old = old:match("(.+).pdf") or old

doc_new = new:match("(.+).pdf") or new

-- getting number of pages in each document ---------------------

local handle = io.popen("pdfinfo " .. doc_old .. ".pdf | grep Pages | awk '{print $2}'")

local pages_old = handle:read("*a")

handle:close()

local handle = io.popen("pdfinfo " .. doc_new .. ".pdf | grep Pages | awk '{print $2}'")

local pages_new = handle:read("*a")

handle:close()

---- converting pdf's into png images ---------------------------

os.execute("convert -density 300 " .. doc_old .. ".pdf " .. doc_old .. ".png")

os.execute("convert -density 300 " .. doc_new .. ".pdf " .. doc_new .. ".png")

-- loop over pages ----------------------------------------------

for i = 0, pages_new-1, 1

do

-- check if page exists in old document ---------------------

if( pages_old+0.0 >= i)

then

-- suffix based on number of pages ----------------------

if( pages_old+0.0 == 1.0 )

then

suffix = ""

else

suffix = "-" .. i

end -- check if only one page

-- calculating diff -------------------------------------

os.execute("compare -compose src " .. doc_old .. suffix .. ".png " .. doc_new .. suffix .. ".png diff" .. suffix .. ".png")

-- getting number of changed pixels ---------------------

local handle = io.popen("convert diff" .. suffix .. ".png -print '%[fx:w*h*(1-mean)]' null:")

local diff_pixel = handle:read("*a")

handle:close()

-- clean up ---------------------------------------------

os.execute("rm " .. doc_new .. suffix .. ".png")

os.execute("rm " .. doc_old .. suffix .. ".png")

-- keeping only images with differences -----------------

if(diff_pixel+0.0 > 0.0)

then

-- print(diff_pixel)

else

os.execute("rm diff" .. suffix .. ".png")

end

end -- check if page exist

end -- loop over pages