read / write EXIF data, simple, no modifications ???

wichtel · Post by **wichtel** » Wed Aug 13, 2008 7:41 am

Hello,

I have searched the web and the boards to find a simple way to retain EXIF information in an image.
All tools and libs I have found so far har way too big.

I just want to load a jpeg image, and save it again without losing the exif information like:

-loadimage
-get exif block
-do something with the picture
-saveimage
-put exif block

Any ideas?

Post by **idle** » Wed Aug 13, 2008 8:01 am

Gdi+ is the thing you need.

http://www.purebasic.fr/english/viewtop ... hlight=gdi

pdwyer · Post by **pdwyer** » Wed Aug 13, 2008 8:04 am

http://www.wotsit.org/download.asp?f=exif&sc=271907762

dige · Post by **dige** » Wed Aug 13, 2008 8:15 am

idle wrote:Gdi+ is the thing you need.

http://www.purebasic.fr/english/viewtop ... hlight=gdi

could you give us a hint? I could'nt find any commands that read / write
exif meta data with gdi :-\

Post by **idle** » Wed Aug 13, 2008 9:22 am

I didn't check to see if its been implemented for PB by Denis but I know that gdi+ does the business.

its as they say, google is your friend!

wichtel · Post by **wichtel** » Wed Aug 13, 2008 10:04 am

Thanks for the answers.
This gets more complicated than expected.
gdi+ is way overpowerd for what I need. Certainly worth looking into it and learn how to use it, but I am more simple minded.

The exif file format link, seemed to be pretty good.
So reading the exif block would not be a problem.
But when you save an image using SaveImage and the UseJPEGImageEncoder you get a JFIF format. I know that EXIF can be in JFIF, but the trick would be now to insert the EXIF data in the JFIF file.

Still trying to make it as simple as possible:

-check for EXIF marker in image
-load the EXIF data block to memory
-load the image using loadimage
-do whatever with the image
-save the image using saveimage
-insert the EXIF block

wichtel · Post by **wichtel** » Wed Aug 13, 2008 1:08 pm

Hey, I got a simple code working.
It consists of 3 blocks.

1. I open a file taken from my camera and read out the EXIF data block.

2. I open a file that has been created from the same image using the PB functions loadimage and saveimage and the JPEGencoder. There I read the entire file.

3. I create a new file and merge der EXIF data with the rest of the file.

Not sure if that is 100% correct, but all my graphic tool still can read the created file and the EXIf info is valid.

Code: Select all

#file=1

file$="D:\oppi\PB4\stempel\dscf0452_jfif.JPG"
If ReadFile(#file, file$) 
  length = Lof(#file)          
  If (ReadByte(#file)&$FF)*256+(ReadByte(#file)&$FF)=$FFD8 ;SOU
    Debug "JPG"
    APP=(ReadByte(#file)&$FF)*256+(ReadByte(#file)&$FF)
    If APP=$FFE1 ;APP1
      Debug "EXIF"
      ssss=(ReadByte(#file)&$FF)*256+(ReadByte(#file)&$FF) ;SSSS
      Debug Hex(ssss)
      FileSeek(#file,4)
      *memEXIF = AllocateMemory(ssss)
      If *memEXIF
        rrrr=ReadData(#file,*memEXIF,ssss)
        Debug Hex(rrrr)
      EndIf
    ElseIf APP=$FFE0 ;APP0
      Debug "JFIF"
      FileSeek(#file,20)
      If (ReadByte(#file)&$FF)*256+(ReadByte(#file)&$FF)=$FFE1 ;APP1
        Debug "EXIF in JFIF"
        ssss=(ReadByte(#file)&$FF)*256+(ReadByte(#file)&$FF) ;SSSS
        Debug Hex(ssss)
        FileSeek(#file,22)
        *memEXIF = AllocateMemory(ssss)
        If *memEXIF
          rrrr=ReadData(#file,*memEXIF,ssss)
          Debug Hex(rrrr)
        EndIf
      EndIf  
    Else   
      Debug "no EXIF, no JFIF"
    EndIf  
  Else
    Debug "no JPG"
  EndIf
  CloseFile(#file)
EndIf  

file$="D:\oppi\PB4\stempel\dscf0452_ost.JPG"
If ReadFile(#file, file$) 
  If (ReadByte(#file)&$FF)*256+(ReadByte(#file)&$FF)=$FFD8 ;SOU
    Debug "JPG"
    If (ReadByte(#file)&$FF)*256+(ReadByte(#file)&$FF)=$FFE0 ;APP0
      Debug "JFIF"
      FileSeek(#file,20)
      If (ReadByte(#file)&$FF)*256+(ReadByte(#file)&$FF)=$FFDB ;FFDB
        FileSeek(#file,0)
        Debug Hex(Lof(#file))
        *memOst=AllocateMemory(Lof(#file))
        If *memOst
          rrrr=ReadData(#file,*memOst,Lof(#file))
          Debug Hex(rrrr)
        EndIf
      EndIf
    Else
      Debug "no JFIF"
    EndIf  
  Else
    Debug "no JPG"
  EndIf
  CloseFile(#file)
EndIf  

file$="D:\oppi\PB4\stempel\dscf0452_ost_exif.JPG"
If CreateFile(#file,file$)
  WriteData(#file,*memOst,20)
  WriteByte(#file,$FF)
  WriteByte(#file,$E1)
  WriteData(#file,*memEXIF,ssss)
  WriteData(#file,*memOst+20,rrrr-20)
  CloseFile(#file)
EndIf

edit: updated code for JFIF

dige · Post by **dige** » Wed Aug 13, 2008 2:16 pm

Hmm, does not work here, coz the App1 marker in my jpg pictures is $FFE0.
But if I use the $FFE0 marker instead, only $10 Bytes will copied..
And what about intel & motorola byte order?

wichtel · Post by **wichtel** » Wed Aug 13, 2008 2:46 pm

@DIGE:

I have updated the code. It is by no means final or perfect, but a simple trick that will probably work for me.

Most pictures right out of a camera are in JPEG-EXIF.
Some pictures are in JPEG-JFIF with EXIF info.

The new code will work with those as well.

I did not care about the byte order yet.

dige · Post by **dige** » Thu Aug 14, 2008 7:35 am

thx, seems to work properly now

Fangbeast · Post by **Fangbeast** » Sun Mar 08, 2009 1:21 pm

Wichtel, don't know if you are still around but...can you decode the bits of exif data?

wichtel · Post by **wichtel** » Sun Mar 08, 2009 5:52 pm

@Fangbeast:
What do you mean with "can you decode exif"?

If you mean if I have written my own EXIF libary - No.
Way too much work. There are so many different info types in there plus vendor specific data...
I thought about extracting just the most needed values. That woul definitly be doable by having a look at the data format and the description in e.g. WiKi. But not yet...

But I could, and you as well, by using an EXIF library. There are several to be found in the net.
e.g. http://www.gimp.org/~tml/gimp/win32/libexif-0.6.16.zip (from gimp)

Fangbeast · Post by **Fangbeast** » Mon Mar 09, 2009 2:51 am

wichtel wrote:@Fangbeast:
What do you mean with "can you decode exif"?

If you mean if I have written my own EXIF libary - No.
Way too much work. There are so many different info types in there plus vendor specific data...
I thought about extracting just the most needed values. That woul definitly be doable by having a look at the data format and the description in e.g. WiKi. But not yet...

But I could, and you as well, by using an EXIF library. There are several to be found in the net.

Hadn't even thought of that, thanks.