Percentage difference between images

Percentage difference between images
You are encouraged to solve this task according to the task description, using any language you may know.

Compute the percentage of difference between 2 JPEG images of the same size. Alternatively, compare two bitmaps as defined in basic bitmap storage.

Useful for comparing two JPEG images saved with a different compression ratios.

You can use these pictures for testing (use the full-size version of each):

50% quality JPEG	100% quality JPEG

The expected difference for these two images is 1.62125%

Ada

<lang ada>type Count is mod 2**64;</lang> 1-norm distance in the luminance space: <lang ada>function "-" (Left, Right : Luminance) return Count is begin

  if Left > Right then
     return Count (Left) - Count (Right);
  else
     return Count (Right) - Count (Left);
  end if;

end "-";</lang> 1-norm distance in the color space multiplied to 3: <lang ada>function "-" (Left, Right : Pixel) return Count is begin

  return (Left.R - Right.R) + (Left.G - Left.G) + (Left.B - Right.B);

end "-";</lang> Mean of 1-norm distances. Constraint_Error is propagated when images have different size. <lang ada>function Diff (Left, Right : Image) return Float is

  Offs_I : constant Integer := Right'First (1) - Left'First (1);
  Offs_J : constant Integer := Right'First (2) - Left'First (2);
  Sum : Count := 0;

begin

  if Left'Length (1) /= Right'Length (1) or else Left'Length (2) /= Right'Length (2) then
     raise Constraint_Error;
  end if;
  for I in Left'Range (1) loop
     for J in Left'Range (2) loop
        Sum := Sum + (Left (I, J) - Right (I + Offs_I, J + Offs_J));
     end loop;
  end loop;
  return Float (Sum) / (3.0 * Float (Left'Length (1) * Left'Length (2)));

end Diff;</lang> Example of use: <lang ada> F1, F2 : File_Type; begin

  Open (F1, In_File, "city.ppm");
  Open (F2, In_File, "city_emboss.ppm");
  Ada.Text_IO.Put_Line ("Diff" & Float'Image (Diff (Get_PPM (F1), Get_PPM (F2))));
  Close (F1);
  Close (F2);</lang>

AutoHotkey

Works with: AutoHotkey_L

uses gdip.ahk <lang AutoHotkey>startup() dibSection := getPixels("lenna100.jpg") dibSection2 := getPixels("lenna50.jpg") ; ("File-Lenna100.jpg") pixels := dibSection.pBits pixels2 := dibSection2.pBits z := 0 loop % dibSection.width * dibSection.height * 4 { x := numget(pixels - 1, A_Index, "uchar") y := numget(pixels2 - 1, A_Index, "uchar") z += abs(y - x) } msgbox % z / (dibSection.width * dibSection.height * 3 * 255 / 100 ) ; 1.626 return

CreateDIBSection2(hDC, nW, nH, bpp = 32, ByRef pBits = "") { dib := object() NumPut(VarSetCapacity(bi, 40, 0), bi) NumPut(nW, bi, 4) NumPut(nH, bi, 8) NumPut(bpp, NumPut(1, bi, 12, "UShort"), 0, "Ushort") NumPut(0, bi,16) hbm := DllCall("gdi32\CreateDIBSection", "Uint", hDC, "Uint", &bi, "Uint", 0, "UintP", pBits, "Uint", 0, "Uint", 0)

dib.hbm := hbm dib.pBits := pBits dib.width := nW dib.height := nH dib.bpp := bpp dib.header := header Return dib }

startup() { global disposables disposables := object() disposables.pBitmaps := object() disposables.hBitmaps := object()

If !(disposables.pToken := Gdip_Startup()) { MsgBox, 48, gdiplus error!, Gdiplus failed to start. Please ensure you have gdiplus on your system ExitApp }

 OnExit, gdipExit

}

gdipExit: loop % disposables.hBitmaps._maxindex() DllCall("DeleteObject", "Uint", disposables.hBitmaps[A_Index]) Gdip_Shutdown(disposables.pToken) ExitApp

getPixels(imageFile) { global disposables ; hBitmap will be disposed later pBitmapFile1 := Gdip_CreateBitmapFromFile(imageFile) hbmi := Gdip_CreateHBITMAPFromBitmap(pBitmapFile1) width := Gdip_GetImageWidth(pBitmapFile1) height := Gdip_GetImageHeight(pBitmapFile1)

mDCo := DllCall("CreateCompatibleDC", "Uint", 0) mDCi := DllCall("CreateCompatibleDC", "Uint", 0) dibSection := CreateDIBSection2(mDCo, width, height) hBMo := dibSection.hbm

oBM := DllCall("SelectObject", "Uint", mDCo, "Uint", hBMo) iBM := DllCall("SelectObject", "Uint", mDCi, "Uint", hbmi)

DllCall("BitBlt", "Uint", mDCo, "int", 0, "int", 0, "int", width, "int", height, "Uint", mDCi, "int", 0, "int", 0, "Uint", 0x40000000 | 0x00CC0020)

DllCall("SelectObject", "Uint", mDCo, "Uint", oBM) DllCall("ReleaseDC", "Uint", 0, "Uint", mDCi) DllCall("ReleaseDC", "Uint", 0, "Uint", mDCo) Gdip_DisposeImage(pBitmapFile1) DllCall("DeleteObject", "Uint", hBMi) disposables.hBitmaps._insert(hBMo) return dibSection }

1. Include Gdip.ahk  ; Thanks to tic (Tariq Porter) for his GDI+ Library

</lang>

C

The read_image function is from here.

<lang c>#include <stdio.h>

1. include <stdlib.h>
2. include <math.h>

/* #include "imglib.h" */

1. define RED_C 0
2. define GREEN_C 1
3. define BLUE_C 2
4. define GET_PIXEL(IMG, X, Y) ((IMG)->buf[ (Y) * (IMG)->width + (X) ])

int main(int argc, char **argv) {

  image im1, im2;
  double totalDiff = 0.0;
  unsigned int x, y;
  
  if ( argc < 3 )
  {
     fprintf(stderr, "usage:\n%s FILE1 FILE2\n", argv[0]);
     exit(1);
  }
  im1 = read_image(argv[1]);
  if ( im1 == NULL ) exit(1);
  im2 = read_image(argv[2]);
  if ( im2 == NULL ) { free_img(im1); exit(1); }
  if ( (im1->width != im2->width) || (im1->height != im2->height) )
  {
     fprintf(stderr, "width/height of the images must match!\n");
  } else {
  /* BODY: the "real" part! */
     for(x=0; x < im1->width; x++)
     {
        for(y=0; y < im1->width; y++)
        {
          totalDiff += fabs( GET_PIXEL(im1, x, y)[RED_C] - GET_PIXEL(im2, x, y)[RED_C] ) / 255.0;
          totalDiff += fabs( GET_PIXEL(im1, x, y)[GREEN_C] - GET_PIXEL(im2, x, y)[GREEN_C] ) / 255.0;
          totalDiff += fabs( GET_PIXEL(im1, x, y)[BLUE_C] - GET_PIXEL(im2, x, y)[BLUE_C] ) / 255.0;
        }
     }
     printf("%lf\n", 100.0 * totalDiff / (double)(im1->width * im1->height * 3) );
  /* BODY ends */
  }
  free_img(im1);
  free_img(im2);

}</lang>

The output on Lenna is:

1.625587

Common Lisp

This is based upon the C version. Strangely enough, the percentage is 1.77% which is off by about a tenth of a percent.

<lang lisp>(require 'cl-jpeg)

the JPEG library uses simple-vectors to store data. this is insane!

(defun compare-images (file1 file2)

 (declare (optimize (speed 3) (safety 0) (debug 0)))
 (multiple-value-bind (image1 height width) (jpeg:decode-image file1)
   (let ((image2 (jpeg:decode-image file2))) 
     (loop for i of-type (unsigned-byte 8) across (the simple-vector image1)
           for j of-type (unsigned-byte 8) across (the simple-vector image2)
           sum (the fixnum (abs (- i j))) into difference of-type fixnum
           finally (return (coerce (/ difference width height #.(* 3 255))
                                   'double-float))))))

 CL-USER> (* 100 (compare-images "Lenna50.jpg" "Lenna100.jpg"))
 1.774856467652165d0</lang>

E

By dividing only at the end, we work with integers only as the sum and avoid floating-point error from adding small numbers (per-pixel difference) to large ones (sum of differences).

<lang e>def imageDifference(a, b) {

 require(a.width() == b.width())
 require(a.height() == b.height())
 def X := 0..!(a.width())
 def Y := 0..!(a.height())
 
 var sumByteDiff := 0
 for y in Y {
   for x in X {
     def ca := a[x, y]
     def cb := b[x, y]
     sumByteDiff += (ca.rb() - cb.rb()).abs() \
                  + (ca.gb() - cb.gb()).abs() \
                  + (ca.bb() - cb.bb()).abs()
   }
   println(y)
 }
 return sumByteDiff / (255 * 3 * a.width() * a.height())

}

def imageDifferenceTask() {

 println("Read 1...")
 def a := readPPM(<import:java.io.makeFileInputStream>(<file:Lenna50.ppm>))
 println("Read 2...")
 def b := readPPM(<import:java.io.makeFileInputStream>(<file:Lenna100.ppm>))
 println("Compare...")
 def d := imageDifference(a, b)
 println(`${d * 100}% different.`)

}</lang>

The result on the provided images is 1.6255930981604882%.

Forth

<lang forth>: pixel-diff ( pixel1 pixel2 -- n )

 over 255 and over 255 and - abs >r 8 rshift swap 8 rshift
 over 255 and over 255 and - abs >r 8 rshift swap 8 rshift
                           - abs r> + r> + ;

bdiff ( bmp1 bmp2 -- fdiff )

 2dup bdim rot bdim d<> abort" images not comparable"
 0e               ( F: total diff   )
 dup bdim * >r    ( R: total pixels )
 bdata swap bdata
 r@ 0 do
   over @ over @ pixel-diff 0 d>f f+
   cell+ swap cell+
 loop 2drop
 r> 3 * 255 * 0 d>f f/ ;

.bdiff ( bmp1 bmp2 -- )

 cr bdiff 100e f* f. ." percent different" ;</lang>

Fortran

<lang fortran>program ImageDifference

 use RCImageBasic
 use RCImageIO

 implicit none

 integer, parameter :: input1_u = 20, &
                       input2_u = 21

 type(rgbimage) :: lenna1, lenna2
 real           :: totaldiff

 open(input1_u, file="Lenna100.ppm", action="read")
 open(input2_u, file="Lenna50.ppm", action="read")
 call read_ppm(input1_u, lenna1)
 call read_ppm(input2_u, lenna2)
 close(input1_u)
 close(input2_u)

 totaldiff = sum(  (abs(lenna1%red - lenna2%red) + &
                    abs(lenna1%green - lenna2%green) + &
                    abs(lenna1%blue - lenna2%blue)) / 255.0 )

 print *, 100.0 * totaldiff / (lenna1%width * lenna1%height * 3.0)

 call free_img(lenna1)
 call free_img(lenna2)

end program ImageDifference</lang>

This gives 1.6555154.

Haskell

This implementation takes PPMs as input. It uses modules defined in Basic bitmap storage and Write ppm file.

<lang haskell>import Bitmap import Bitmap.Netpbm import Bitmap.RGB

import Control.Monad import Control.Monad.ST import System.Environment (getArgs)

main = do

   [path1, path2] <- getArgs
   image1 <- readNetpbm path1
   image2 <- readNetpbm path2
   diff <- stToIO $ imageDiff image1 image2
   putStrLn $ "Difference: " ++ show (100 * diff) ++ "%"

imageDiff :: Image s RGB -> Image s RGB -> ST s Double imageDiff image1 image2 = do

     i1 <- getPixels image1
     i2 <- getPixels image2
     unless (length i1 == length i2) $
         fail "imageDiff: Images are of different sizes"
     return $
         toEnum (sum $ zipWith minus i1 i2) /
         toEnum (3 * 255 * length i1)
 where (RGB (r1, g1, b1)) `minus` (RGB (r2, g2, b2)) =
           abs (r1 - r2) + abs (g1 - g2) + abs (b1 - b2)</lang>

MAXScript

<lang maxscript>fn diffImages = ( local img1 = selectBitmap caption:"Select Image 1" local img2 = selectBitmap caption:"Select Image 2" local totalDiff = 0 for i in 0 to (img1.height-1) do ( local img1Row = getPixels img1 [0, i] img1.width local img2Row = getPixels img2 [0, i] img2.width

for j in 1 to img1.width do ( totalDiff += (abs (img1Row[j].r - img2Row[j].r)) / 255.0 totalDiff += (abs (img1Row[j].g - img2Row[j].g)) / 255.0 totalDiff += (abs (img1Row[j].b - img2Row[j].b)) / 255.0 ) ) format "Diff: %\%\n" (totalDiff / ((img1.width * img1.height * 3) as float) * 100) )</lang>

J

<lang j> require 'media/image3'

  'Lenna50.jpg' (+/@,@:|@:- % 2.55 * */@$@])&read_image 'Lenna100.jpg'

1.62559</lang>

OCaml

Library: glMLite

<lang ocaml>#! /usr/bin/env ocaml

1. directory "+glMLite/"
2. load "jpeg_loader.cma"
3. load "bigarray.cma"

open Jpeg_loader

let () =

 let img1, width1, height1, col_comp1, color_space1 = load_img (Filename Sys.argv.(1))
 and img2, width2, height2, col_comp2, color_space2 = load_img (Filename Sys.argv.(2)) in

 assert(width1 = width2);
 assert(height1 = height2);
 assert(col_comp1 = col_comp2);  (* number of color components *)
 assert(color_space1 = color_space2);

 let img1 = Bigarray.array3_of_genarray img1
 and img2 = Bigarray.array3_of_genarray img2 in

 let sum = ref 0.0
 and num = ref 0 in

 for x=0 to pred width1 do
   for y=0 to pred height1 do
     for c=0 to pred col_comp1 do
       let v1 = float img1.{x,y,c}
       and v2 = float img2.{x,y,c} in
       let diff = (abs_float (v1 -. v2)) /. 255. in
       sum := diff +. !sum;
       incr num;
     done;
   done;
 done;

 let diff_percent = !sum /. float !num in
 Printf.printf " diff: %f percent\n" diff_percent;

</lang>

Python

This example is incorrect. Please fix the code and remove this message. Details: Trying to import Image results in: ImportError: No module named Image

Works with: python version 2.x

<lang python>from itertools import izip import Image

i1 = Image.open("image1.jpg") i2 = Image.open("image2.jpg") assert i1.mode == i2.mode, "Different kinds of images." assert i1.size == i2.size, "Different sizes."

pairs = izip(i1.getdata(), i2.getdata()) if len(i1.getbands()) == 1:

   # for gray-scale jpegs
   dif = sum(abs(p1-p2) for p1,p2 in pairs)

else:

   dif = sum(abs(c1-c2) for p1,p2 in pairs for c1,c2 in zip(p1,p2))

ncomponents = i1.size[0] * i1.size[1] * 3 print "Difference (percentage):", (dif / 255.0 * 100) / ncomponents</lang>

REBOL

<lang REBOL>REBOL [ Title: "Percent Image Difference" Author: oofoe Date: 2009-12-31 URL: http://rosettacode.org/wiki/Percentage_of_difference_between_2_images ]

Load from local storage. Un/comment as preferred.

a

load-image %lenna50.jpg

b

load-image %lenna100.jpg

Download from rosettacode.org.

a: load-image http://rosettacode.org/mw/images/3/3c/Lenna50.jpg b: load-image http://rosettacode.org/mw/images/b/b6/Lenna100.jpg

if a/size <> b/size [print "Image dimensions must match." halt]

Compute difference. REBOL has built-in image processing as part of

its GUI package that I can take advantage of here

diff: to-image layout/tight [image a effect [difference b]]

Calculate deviation. I use 'repeat' to rip through the image pixels

(it knows how to deal with images) and sum, then average. Note that

I can treat the image like an array to get number of pixels.

t: 0 repeat p diff [t: t + p/1 + p/2 + p/3] print rejoin ["Difference: " 100 * t / (255 * 3 * length? diff) "%"]

Optional

Since I now have a difference image, I may as well show

it. Use the buttons or keys 'a', 'b' and 'd' to switch between the

various images.

flip: func [ "Change to new image and label." name [word!] "Image to switch to." ][x/text: rejoin ["Image " name] x/image: get name show x]

Because the differences between the images are very small, I enhance

the diff with a high contrast to make the result easier to

see. Comment this out for the "pure" image.

diff: to-image layout/tight [image diff effect [contrast 100]]

view l: layout [ x: image diff across button "a" #"a" [flip 'a] button "b" #"b" [flip 'b] button "difference" #"d" [flip 'diff] ]</lang>

Output:

Difference: 1.62559309816049%

Note that this image has been contrast enhanced to highlight the differences.

Ruby

uses the raster_graphics library <lang ruby>require 'raster_graphics'

class RGBColour

 # the difference between two colours
 def -(a_colour)
   (@red - a_colour.red).abs +
   (@green - a_colour.green).abs +
   (@blue - a_colour.blue).abs
 end

end

class Pixmap

 # the difference between two images
 def -(a_pixmap)
   if @width != a_pixmap.width or @height != a_pixmap.height
     raise ArgumentError, "can't compare images with different sizes"
   end
   sum = 0
   each_pixel {|x,y| sum += self[x,y] - a_pixmap[x,y]}
   Float(sum) / (@width * @height * 255 * 3)
 end

end

lenna50 = Pixmap.open_from_jpeg('Lenna50.jpg') lenna100 = Pixmap.open_from_jpeg('Lenna100.jpg')

puts "difference: %.5f%%" % (100.0 * (lenna50 - lenna100))</lang>

produces:

difference: 1.62559%

Tcl

Library: Tk

This version uses the Img package, but only to provide a convenient JPEG loader; it's utterly unnecessary for the process of actually computing the difference. <lang tcl>package require Tk

proc imageDifference {img1 img2} {

   if {

[image width $img1] != [image width $img2] || [image height $img1] != [image height $img2]

   } then {

return -code error "images are different size"

   }
   set diff 0
   for {set x 0} {$x<[image width $img1]} {incr x} {

for {set y 0} {$y<[image height $img1]} {incr y} { lassign [$img1 get $x $y] r1 g1 b1 lassign [$img2 get $x $y] r2 g2 b2 incr diff [expr {abs($r1-$r2)+abs($g1-$g2)+abs($b1-$b2)}] }

   }
   expr {$diff/double($x*$y*3*255)}

}

1. Package only used for JPEG loader

package require Img image create photo lenna50 -file lenna50.jpg image create photo lenna100 -file lenna100.jpg puts "difference is [expr {[imageDifference lenna50 lenna100]*100.}]%" exit ;# Need explicit exit here; don't want a GUI</lang> It produces this output:

difference is 1.6255930981604882%

Vedit macro language

This implementation compares two BMP images.

<lang vedit>Chdir("|(USER_MACRO)\Rosetta\data") File_Open("Lenna50.bmp", BROWSE)

1. 10 = Buf_Num // #10 = buffer for 1st image

File_Open("Lenna100.bmp", BROWSE)

1. 20 = Buf_Num // #20 = buffer for 2nd image

Goto_Pos(10) // offset to pixel data Goto_Pos(Cur_Char + Cur_Char(1)*256) Buf_Switch(#10) Goto_Pos(10) Goto_Pos(Cur_Char + Cur_Char(1)*256)

1. 15 = 0 // #15 = difference
2. 16 = 0 // #16 = total number of samples

While(!At_EOF) {

   #11 = Cur_Char; Char
   Buf_Switch(#20)
   #21 = Cur_Char; Char
   #15 += abs(#11-#21)
   #16++
   Buf_Switch(#10)

}

1. 19 = #15 / (#16*256/100000)

M("Sum of diff: ") NT(#15) M("Total bytes: ") NT(#16) M("Difference: ") NT(#19/1000,LEFT+NOCR) M(".") NT(#19%1000,LEFT+NOCR) M("%\n")

Buf_Switch(#10) Buf_Quit(OK) Buf_Switch(#20) Buf_Quit(OK)</lang>

Output, when comparing the Lenna images that were converted to BMP:

Sum of diff: 3259967
Total bytes: 786432
Difference:  1.619%