[Ssc-dev] Jpeg Redaction Library update

[Andrew Senior]

On Thu, Jan 5, 2012 at 11:52 AM, Nathan of Guardian <
nathan at guardianproject.info> wrote:

> On 01/04/2012 05:45 PM, Andrew Senior wrote:
> > 1) the "Unknown Marker" problem that Nathan flagged should be fixed.
>
> Great. Will test right away, as I want to push an update out that works
> better on the Samsung (which is where I found the issue).
>
> > 2) There was a problem with solid redaction using black rather than
> > grey. The big step changes at the edge of such redaction regions were
>
> Looks fine!
>
> > 3) The code now supports one kind of makernote (Panasonic) making them
> > relocatable.
>
> Can you explain this a bit more?
>
> Makernote is the block of manufacturer-proprietary information stored in
the JPEG file. On my android devices, I've not seen them, but digital
cameras usually write them. It is easy to preserve them since one is given
the length of the data block, but in some formats there are internal
pointers that are corrupted if the block is written out verbatim at a
different point in a new JPEG file. The new code can parse the Panasonic
makernote and thus write it out with the correct pointers for a new
location. I think it will be easy to do Canon too, but am not sure about
other manufacturers (and indeed some manufacturers have multiple
formats...) The default of preserving the block of data verbatim seems fine
in general though- exiftool seems to be able to handle the pointer errors
just flagging a warning.

For Obscuracam we delete the makernote anyway as it can have information
like owner name in it.


> +n
>
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