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Thread: Comments in PNG files

  1. #1
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    Default Comments in PNG files

    I scan paper photos and drawings to PNG files. I want to have a high resolution version that is free of JPEG artifacts. For some purposes, I may downsize to a JPEG. I would like to have identifying information in the PNG file. The PNG standard has tEXt chunks for this purpose, but I have not found a program that uses the tEXt chunks. I would like to have, as a minimum, a long comment in the PNG that would get converted to the corresponding EXIF comment when the file is converted.

    I thought of using IPTC comments on a TIF file. Irfanview does not see an IPTC comment after I have put one in the TIF with Photoshop Elements. For no particular reason I prefer PNG over TIF.

  2. #2
    Hobby User Sprintdriver's Avatar
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    PNG (espechially when using pngout) makes smaller files compared to tif files.

    I'v never heard of any programs that is capable to put comment to PNG files.

    However you have two quite obvious alternatives.
    • Assumed that you store the files on a NTFS partition, you can always add a comment to the image - File --> Properties --> Summary --> Comment.
    • Or you can simply keep a text file in the same directory as the image file is stored into where you write comments to the files.
    If it hurts not to drint, don't waste the bottle then.

  3. #3
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    Quote Originally Posted by Sprintdriver View Post
    I'v never heard of any programs that is capable to put comment to PNG files.
    Win7 Explorer allows to put "Date Taken" in PNG files (and destroys the APNG structure doing this).
    Photoshop is able to add comments using XMP standard.

    Irfan likes to add XMP support at some time.

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    Quote Originally Posted by Sprintdriver View Post
    I'v never heard of any programs that is capable to put comment to PNG files.
    I just searched and found a couple. However, they are command line programs. I would be working blind putting on comments.

    I have a copy of the PNG standard version 1.0, March 1997. It fully describes the tEXt chunks that would be used for comments. It seems strange that this feature is so little used. The current PNG standard 2.0 does not mention XMP

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    Quote Originally Posted by bob thrun View Post
    I just searched and found a couple. However, they are command line programs. I would be working blind putting on comments.

    I have a copy of the PNG standard version 1.0, March 1997. It fully describes the tEXt chunks that would be used for comments. It seems strange that this feature is so little used. The current PNG standard 2.0 does not mention XMP
    If you read the standard you will see that there are only hints about some predefined keywords and that the text area does not allow Unicode. PNG does not mention any of the standards which allow to integrate metadata to file. But the ISO standard XMP does describe how to embed XMP to PNG and other file formats (even the quite old gif format).

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    Quote Originally Posted by impdf View Post
    If you read the standard you will see that there are only hints about some predefined keywords and that the text area does not allow Unicode.formats
    The PNG 2.0 iTXt chunks are Unicode. In fact, the XMP stuff is contained within an iTXt chunk. XMP uses a private keyword: XML.com.adobe.xmp . The XMP keyword is an advertisement for Adobe! XMP adds a layer of encapsulation to the comments for no benefit that I can see. I would be happy with just a single free-form comment where I could identify people and places.

  7. #7
    IV Beginner Jaff's Avatar
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    Default Insert comments in PNG with TweakPNG

    You can put comments inside PNG with TweakPNG iTXt chunks (author, comment, copyright etc)
    Imi este indiferent ce cred ceilalti despre mine, caci oricum fiecare crede ce-i convine lui si nu ceea ce e real,
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