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PAEz

Whats a good way to get unique checksums for small pngs? [Solved]

7 posts in this topic

#1 ·  Posted (edited)

Im trying to generate unique checksums for small pngs and alot of the checksums arent unique.

Ive attached what I have so far, sorry I didnt make a simpler example but I thought it might help to see the context its used in anywayz (ChromeDLL.au3 is the one of interest)....only prob is you need the chrome.dll in the scripts directory and I didnt include it as its about 20meg, hopefully you have Chrome installed :)...and if not install it, Chrome Rocks! :mellow:

I dont care if whatever is used to generate the checksum is a little slow...as long as their unique

Edit: Attachment deleted, not needed anymore and was to big. Solution at the end of this thread.

Edited by PAEz

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I tried md5, sha1 and crc from here...

...and they all had some images getting the same checksums, so maybe its something Im doing wrong?

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#4 ·  Posted (edited)

I tried md5, sha1 and crc from here...

...and they all had some images getting the same checksums, so maybe its something Im doing wrong?

Maybe it's some padding issue only.

I don't use these functions so post some images and related reproducing code for generating its MD5 checksum and somebody will help you fix the issue.

Edited by Zedna

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Sorry I think its my total lack of knowing whats going on now :mellow:

I should prolly delete this thread until I get a better understanding of how to get at the pixels first.

Sorry to waste your time and thanks very much for sharing some of it with me.

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I should prolly delete this thread until I get a better understanding of how to get at the pixels first.

Don't delete/clear posts!

It's not preferred way here to wipe out previous posts.

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#7 ·  Posted (edited)

I meant delete the whole thread, Id never delete individual posts...I hate that too.

Better is to post a solution for the next person who finds this thread from a search, so here's the solution Im using.....

#include <File.au3>
#include <GDIPlus.au3>
#include <Array.au3>
;http://www.autoitscript.com/forum/topic/76976-md5sha1crc32rc4base64xxtea-machine-code-version/page__hl__md5__fromsearch__1
#include "md5.au3"
 
$testfile ='C:\Documents and Settings\Admin\My Documents\16.png'
 
MsgBox(0, "PNGs Checksum", PNGFileChecksum($testfile))
 
Func PNGFileChecksum($file)
If FileIsPNG($file) Then
Local $PNGChecksum = _MD5(_GetImagePixels($file))
Return $PNGChecksum
EndIf
Return False
EndFunc
 
Func _GetImagePixels($sImage)
    Local $hImage, $hBmp, $iW, $iH
    Local $tBD, $iWidth, $iHeight, $iStride, $iFmt
    Local $pData, $tPixels, $xBytes
    Local $avPixels, $hFile

    ;If @error Then Return SetError(1, 1, 0)

    _GDIPlus_Startup()

    $hImage = _GDIPlus_ImageLoadFromFile($sImage)
    If @error Then Return SetError(1, 2, 0)

    $iW = _GDIPlus_ImageGetWidth($hImage)
    $iH = _GDIPlus_ImageGetHeight($hImage)
    ; Would have thought the next line would create a 32bit image but it doesnt, 8bit images stayed 8bit
    ;$hBmp = _GDIPlus_BitmapCloneArea($hImage, 0, 0, $iW, $iH, $GDIP_PXF32ARGB)
    ; And I need to turn them to 32bit, or 8bit images that are only different in the pallette could register identical
    ; So now I create a 32bit image and copy the image to it making it 32bit and then palletes dont matter
    $hBmp = _GDIPlus_BitmapCreateFromScan0($iW, $iH)
    $hGraphic = _GDIPlus_ImageGetGraphicsContext($hBmp)
    _GDIPlus_GraphicsDrawImage($hGraphic, $hImage, 0, 0)
    ;_GDIPlus_ImageSaveToFile($hBmp,$sImage&'.2.png') ; test to make sure they are 32bit
    $tBD = _GDIPlus_BitmapLockBits($hBmp, 0, 0, $iW, $iH, BitOR($GDIP_ILMREAD, $GDIP_ILMWRITE), $GDIP_PXF32ARGB)

    ;$iWidth = DllStructGetData($tBD, 1)
    ;$iHeight = DllStructGetData($tBD, 2)
    ;$iStride = DllStructGetData($tBD, 3)
    ;$iFmt = DllStructGetData($tBD, 4)
    $pData = DllStructGetData($tBD, 5)

    $tPixels = DllStructCreate("byte[" & $iW * $iH * 4 & "]", $pData)
    $xBytes = DllStructGetData($tPixels, 1)

    _GDIPlus_BitmapUnlockBits($hBmp, $tBD)

    _GDIPlus_BitmapDispose($hBmp)
    _GDIPlus_ImageDispose($hImage)
    _GDIPlus_GraphicsDispose($hGraphic)
    _GDIPlus_Shutdown()
    Return $xBytes
EndFunc   ;==>_GetImagePixels
 
Func _GDIPlus_BitmapCreateFromScan0($iWidth, $iHeight, $iStride = 0, $iPixelFormat = 0x0026200A, $pScan0 = 0)
Local $aResult = DllCall($ghGDIPDll, "uint", "GdipCreateBitmapFromScan0", "int", $iWidth, "int", $iHeight, "int", $iStride, "int", $iPixelFormat, "ptr", $pScan0, "int*", 0)
If @error Then Return SetError(@error, @extended, 0)
Return $aResult[6]
EndFunc   ;==>_GDIPlus_BitmapCreateFromScan0
 
Func FileIsPNG($pngfile)
Local $file = FileOpen($pngfile, 16)
; Check if file opened for reading OK
If $file = -1 Then
  MsgBox(0, "Error", "Unable to open file " & $pngfile)
  Exit
EndIf
$chars = FileRead($file, 4)
FileClose($file)
If $chars = "0x89504E47" Then
  Return True
EndIf
Return False
EndFunc   ;==>FileIsPNG
Edited by PAEz

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