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Joseph Chamberlain, DDS wrote:
> On 12/9/05 2:47 AM, in article
> 1134125249.323369.56800@g49g2000cwa.googlegroups.com, "Barry Pearson"
> wrote:
>
> > That appears to mix up two concepts: the location of the cache
> > (centralised or distributed); and the location of ACR settings and
> > other metadata (database or sidecar XMP files or within a DNG file).
> > The former is a Bridge preference. The latter is an ACR preference
> > combined with a choice of file-type.
[snip]
> Isn't the purpose of .xmp sidecar files to hold or store "all" information
> that relates to the raw images ?
The XMP metadata holds information that should have a long association
with the image. The cache is mainly to speed up Browser or Bridge. For
example, the cache, I believe, holds the thumbnails in a rapidly
accessible form. The cache can be purged, because the thumbnails can be
regenerated from the DNG later.
> My impression was that sidecar files held raw conversion information created
> by Camera Raw but also held information attached to the raw images by Bridge
> such as sort order, keywords and other metadata.
Not all of that. For example, the sort-order isn't held with the image
itself, because if you hand that file to someone else, the sort order
is meaningless.
The distributed cache for Bridge is held in 2 files in each folder,
(not per image):
Adobe Bridge Cache.bct
Adobe Bridge Cache.bc
There is sometimes another file in a folder, (not per image), and from
its name appears to be related to the sort order:
.BridgeSort
The XMP sidecar is in text form, and is worth having a look at to see
what is there. If you open a DNG file with Word, (or presumable any
text editor or other word processor), you should see the same text in
it, if it is holding XMP metadata. (Word won't show the sensor data, of
course! But the XMP metadata in in clear form).
> Although I am tempted to use DNG and find the idea the best approach to
> working with RAW images, I must confess that at this time I am a little
> skeptical of committing my RAW files to the DNG file format and the DNG
> converter. I am afraid that either the file format itself or the converter
> may corrupt my images and prevent me from extracting my original RAW files
> in the future should I need to do so.
You need to be comfortable with what you do. I've been doing this for
several months with success, but I am not going to try a "hard sell" to
persuade you to do this!
I do my own test on ACR and the DNG Converter when they are released,
and don't adopt them until I am satisfied that they work OK. I don't
just download and start using them. I check that ACR appears to give
the sort of results I expect. And I test the following routes, to
ensure that the DNG Converter itself is not screwing things up. (I test
by using blending mode "difference" on the two versions, and verifying
that all pixels are zero).
PEF > ACR > PSD (layer 0)
PEF > DNG > ACR > PSD (layer 1)
[snip]
> I remember reading Bruce Fraser's book on Camera Raw for Photoshop CS2 and
> he mentions the two options. One to have a centralized cache or database
> with all the metadata that applies to the RAW files or to have a distributed
> one where each sidecar file is placed in the same folder where the image it
> is related to is located. This is the database I am referring to.
What is important is that the "database" and the "cache" are different
things. You can actually safely delete the cache, (or copy your DNGs
without exporting the cache), and still retain your settings.
But I have just looked at page 70 of Bruce's CS2 book, at "Export
Settings". And I believe he has made a mistake! He says "when you have
the Camera Raw Preferences set to save edits in the Camera Raw cache".
Go and have a look at Camera Raw Preferences, at the drop-down box for
the location of settings - it (correctly) says "Camera Raw database".
You have a perfect right to be confused.
The database is a file called "Database" in "Documents and
SettingsApplication DataAdobeCameraRaw".
The central cache appears to be in the "Documents and
SettingsApplication DataAdobeCameraRawCache" folder.
[snip]
> How can one export in a single sidecar file "ALL" settings and information
> that has been applied to an image so that in case this image and the
> corresponding sidecar file are transferred to another system Bridge and
> Photoshop CS2 will open the image with the same settings that were applied
> to the image in the first system ?
[snip]
Data that is specific to one image, and needs to be retained even if
the cache is lost or purged, is held in the database or sidecars or
inside the DNG itself. Hence edits, settings, etc. If you hold it in
the database, you then need to export it so that it can be copied
across.
Data that can be thrown away and remade, or relates to a set of images,
such as thumbnails & previews, or sort parameters, is held in the
cache. They don't need to be copied across, or don't really make sense
to copy across.
Some data appears to vary according to file type: for example, I notice
that ratings are held in the DNG file as XMP metadata. I suppose that
makes sense, but I believe that in some cases ratings are held in the
cache. (?)
It is not a simple picture.
--
Barry Pearson
http://www.barry.pearson.name/photography/
http://www.birdsandanimals.info/
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