Compare Images / Delta Images

[kevin]

  Compare Images / Delta Images

  This source code snippet runs through and compares two same sized images together.    The idea here being that when making media for our game, it might be easier to create a number of variations of a background picture,  by simply saving the entire picture each time,  but from a media stand point, this can soon blow out the size of the distribution.   So this routine makes a transparent version of the second image that and be drawn over the first image to recreate the original second image.  So the second image becomes the difference between the two images.   Which is sometimes called a delta frame.

 

PlayBASIC Code: [Select]

   ; -------------------------------------------   
   ; a pair of images to compare
   ; -------------------------------------------   
   Sky1=MakeIMage1(800,600)

   Sky2=MakeIMage1(800,600)
   rendertoimage Sky2
   loadfont "arial",2,100
   setfont 2
   centertext 400,300,"Hello World"
   setfont 1
   rendertoscreen
   
   rgbmaskimage sky1,$00ffffff
   rgbmaskimage sky2,$00ffffff
   


   ; -------------------------------------------   
   ; Compares images
   ; -------------------------------------------   

   MaskCOlour=$ff00ff
   
   Dim IMage1(1,1)
   Dim IMage2(1,1)

   Read_Pixels(IMage1(),Sky1)
   Read_Pixels(IMage2(),Sky2)
   Sync

   drawimage sky1,0,0,false
   if Compare_Images(IMage1(),IMage2(),MaskColour)   

            select Paint_Array(Sky2, IMage2(),MaskColour)

                  case 0
                        print "Images are identical."
                     
                  case 1
                        print "Section Of IMages are the same"
   
            endselect   

   else
         print "error:images are not the same size."
   endif
   

   print "IMage two now hold only the pixels that are different from image 1"
   
   Sync
   waitkey


   ; -------------------------------------------   
   ; Demo images
   ; -------------------------------------------   

   Setfps 10
   
   Transparent=true
   Do
      cls 
      drawimage Sky1,0,0,false

      if Spacekey()
         drawimage Sky2,0,0,transparent
      endif

      if EnterKey()
         Transparent=1-   Transparent      
         Flushkeys
      endif

      print "Space to Show Masked IMage 2 over image 1"   
      print "enter Toggle transparent mode"
   
      Sync   
   loop
   



Function MakeIMage1(Width,Height)
   IMage=NewImage(Width,Height,2)

   rendertoimage image
   shadebox 0,0,width,height,$203040,$406040,$ff4050,$405550
   
   rendertoscreen   

EndFunction IMage
   
   
   
Function Paint_Array(TargetIMage,IMage(),MaskColour)

      rendertoimage TargetIMage
      IMageMaskCOlour TargetIMage,MaskCOlour
      cls MaskColour
      

      RowCount=0

      Width   =GetArrayElements(Image(),1)
      Height   =GetArrayElements(IMage(),2)

      rectx1=Width
      recty1=Height
      rectx2=0
      recty2=0

      lockbuffer
      For ylp=0 to height-1

         UsedRow=false
         For Xlp=0 to Width-1
               pixel=IMage(xlp,ylp)
               if pixel<>maskColour
                  dotc xlp,ylp,Pixel
                  if xlp<RectX1 then RectX1=xlp
                  if xlp>RectX2 then RectX2=xlp
                  UsedRow=true
               endif
            
         next

         if UsedRow
            if ylp<RectY1 then RectY1=ylp
            if ylp>RectY2 then RectY2=ylp
            RowCount++
         endif
      next
      unlockbuffer

      rendertoscreen


      ; draw the second image, over the first image with the zone around it
      drawimage targetimage ,0,0,true

      ; high light the area around 
      box rectx1,recty1,rectx2,recty2,false


EndFunction RowCount
   

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