Centralized x Distributed cache in Bridge.

Joseph Chamberlain, DDS wrote:

(If you really want to ask questions in two forums, it is better to cross-post than multi-post).

Dear members:

I am faced with the choice of selecting either centralized cache or distributed cache for Bridge.

The benefit of using distributed cache is that the sidecar .xmp file is saved in the same folder where the images are making it simple to export it along with the images when they need to be transferred to another location in the system or transferred to another computer. The problem however is that every folder ends up having two files instead of one for every image with only the file extension being different. I remember the first raw file format released by Canon and how annoying it was to deal with one .CRW and one .THM file for every image in the folder.

[snip]

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.

If you want the simplest management of the ACR settings and other metadata, with no need to extract them from the database, (which is where they can be held – not the cache), and no XMP sidecars, use DNG. Then the XMP metadata that would have been held in the sidecar is held in the DNG file itself.

This ability to hold a full range of metadata within DNG files is one of the best reasons for switching to a DNG-based workflow, if the tools you use permit it.

—
Barry Pearson
http://www.barry.pearson.name/photography/
http://www.birdsandanimals.info/

On 12/9/05 2:47 AM, in article
, "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.

If you want the simplest management of the ACR settings and other metadata, with no need to extract them from the database, (which is where they can be held – not the cache), and no XMP sidecars, use DNG. Then the XMP metadata that would have been held in the sidecar is held in the DNG file itself.

This ability to hold a full range of metadata within DNG files is one of the best reasons for switching to a DNG-based workflow, if the tools you use permit it.
—
Barry Pearson

Isn’t the purpose of .xmp sidecar files to hold or store "all" information that relates to the raw images ?

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.

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.

For this reason I thought about the possibility of working with the original RAW images and managing the sidecar files whenever I needed to move the files to another location in the system or export them to another system, external storage device or removable medium.

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.

Your statement has me a little confused when you say:

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.

Isn’t information attributed by Bride to a RAW image supposed to be incorporated into the sidecar file along with all other metadata that relates to that image ?

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 ?

Your statement leads me to believe that there may be more than 1 sidecar file – one created by ACR and the other by Bridge.

Thanks again for the help and detailed post.

Best regards,

Joseph

—

Dr. Joseph Chamberlain
Oral and Maxillofacial Surgery

Joseph Chamberlain, DDS wrote:

On 12/9/05 2:47 AM, in article
, "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 Settings\<user>\Application Data\Adobe\CameraRaw".

The central cache appears to be in the "Documents and Settings\<user>\Application Data\Adobe\CameraRaw\Cache" 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/