Re: EXIF support in PNG

The report about the large resolution number in EXIF was on the ImageMagick
"issues" at github:
https://github.com/ImageMagick/ImageMagick/issues/351
The "bug" was that they had used a comma for decimal point:

$ exiftool -a image.jpg | grep Resolution
Resolution Unit                 : cm
X Resolution                    : 28
Y Resolution                    : 28
X Resolution                    : 71
Y Resolution                    : 71
Resolution Unit                 : inches
X Resolution                    : 28,346
Y Resolution                    : 28,346
Resolution Unit                 : Centimeter

Glenn

On Fri, Jan 13, 2017 at 6:55 AM, Glenn Randers-Pehrson <[email protected]>
wrote:

> Very recently I saw a bug report about ImageMagick; someone writing a PNG
> with GIMP mixed up resolution units and put 11000 pixels per cm, resulting
> in IM running out of memory trying to expand the image.  I'm not suggesting
> that that's a bug that we need to fix, but it is s security issue to be
> aware of.
>
> Sorry, I can't find that bug report now...
>
> Glenn
>
> Glenn
>
> On Thu, Jan 12, 2017 at 10:51 PM, John Bowler <
> [email protected]> wrote:
>
>> This github project:
>>
>> https://github.com/jbowler/jpegtopng
>>
>> Now contains a Makefile and source to build three programs:
>>
>> jpegtopng: requires an installed -ljpeg and -lz
>> jpegdump: stand-alone hack program to dump a JPEG
>> pngdumpmeta: requires -lpng and -lexiv2
>> The first file takes any JPEG with an APP1 EXIF marker and converts it
>> to an exIf chunk matching Willems previously supplied example image.
>>
>> The second is just a way of looking inside a JPEG, at least for the
>> markers it understands (it also produces lots of warnings with -Wall).
>>
>> The third is the real example program; it decodes the exIf chunk
>> (that's just a few lines of code, mostly recognizing that it is an
>> exIf from the header) then it prints the contents using the Exiv2
>> library; that's about 20 lines of code as well.
>>
>> It also prints an ISO XMP chunk.  Quite a lot of the code is to verify
>> UTF-8 data (that's in the directory hutf8/), XMP is just raw XML so it
>> just prints so long as it is valid.
>>
>> It will also print text chunks; either a list of the keywords or the
>> text one of them contains.  It prints the text in UTF-8; so it
>> converts the Latin1 text in tEXt or zTXt chunks into UTF-8 on-the-fly.
>>
>> It only does one thing at once.  The first and last programs read from
>> stdin and write to stdout (no file management).
>>
>> Next I'm going to look at adding support for the text chunk used to
>> output Exif from Image/GraphicsMagick and DigiKam.  The sample code in
>> the pngexif directory already does that but I haven't tested it.  It's
>> 132 lines of code as opposed to 59 when the data is in an unknown
>> chunk; decoding the format about doubles the amount of code required
>> (the rest of it is comments and looking though the text or unknown
>> chunk lists.)
>>
>> I haven't verified compilation against libpng12 yet, but I don't
>> anticipate any problems.
>>
>> John Bowler
>>
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