A couple of notes on this:

Photoshop doesn't strip EXIF because we didn't have requests to do this
other than when saving for web to minimize space. People have expressed far
more concern about preserving EXIF than stripping it. If we hear demand for
stripping EXIF outside of save for web, we'll certainly consider adding
that.

Photoshop doesn't edit EXIF data because it is not generally possible to do
so without destroying it. There's no padding, so if you want to change a
value so that it takes up more or less space than it previously did (like a
title or the photographer's name or whatever), things that come after that
value in the EXIF data get moved. But EXIF data can contain private camera
manufacturer data anywhere -- data that Photoshop can't understand, and some
of that data contains locations of other things within the block of EXIF. So
if you change the length of text in a publicly documented field, you may
corrupt other manufacturer-private data. There's no way to tell. The only
safe things to do with EXIF are to keep all of it, delete all of it, or
write just a few fields that we understand, and those are the options that
Photoshop offers. So Photoshop is unlikely to ever offer general EXIF data
editing.

One of the other complications of metadata is that many files contain
multiple kinds of metadata that represent the same or overlapping things --
EXIF, IPTC, XMP. There are standards groups that try to sort out whether the
description field of one metadata standard should mean the same thing as the
"caption" field of another. Photoshop has rules for what happens when there
are multiple kinds of metadata and they don't agree (there are no standards
here). Some of these kinds of metadata are not extensible (IPTC) or are
fragile (EXIF). That's the reason Adobe's pushing XMP as the metadata
standard -- it's:
* editable
* publicly documented, free
* user extensible
* supports manufacturer private data that leaves public data editable
* can be extracted from files and even edited, even if you can't read the
containing file format. That is, somebody can write a program that extracts
and provides editing (with some restrictions) for the XMP metadata in
Photoshop files, JPEGs, TIFFs, etc. even if you have no idea how to read
Photoshop files or JPEGs. (It's usually much faster if you *do* know how to
read the containing file, but it's important that you can get the metadata
out of any file).

So Photoshop always tries to write and prefer XMP, and that's what's used to
hold the keywords you assign in the file browser or the data from extra,
custom panels you add to the fileinfo dialog.

Russell


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