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Author Topic: DNG and colorspace  (Read 13704 times)
MarkP
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« on: August 07, 2006, 01:57:22 AM »


I just discovered that the colorspace metadata field in my DNG's
has been changed to sRGB from  Adobe RGB shown in the
NEF just prior to conversion.

Any thoughts on this?

Thanks in advance.

Mark
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Michael_S
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« Reply #1 on: August 07, 2006, 05:15:26 AM »

Mark,
This is an interesting post.  Afer reading your statements, I went to a folder with a couple dozen DNG files.  In my case, both the "Color Mode" and "Color Profile" tags are blank for all files.  Are these the tags that were switched for your files?
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danaltick
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« Reply #2 on: August 07, 2006, 05:45:18 AM »

Raw files have no colorspace so to speak.  Raw data is linearly mapped.  A color working space is applied when the image is imported into Photoshop.  At that time the linear data is gamma mapped to the space you have selected in ACR.  Working on the linear data iis less destructive than working on the gamma mapped data... one of the advantages to shooting Raw.

Dan
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AlanDunne
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« Reply #3 on: August 10, 2006, 09:34:45 AM »

Note however that the embedded jpeg preview in the DNG (assuming you use that feature, and you would if you adhere to the principles in the DAM Book) does have a color space and it is sRGB. If you import a DNG file into IVMP for example and look at the "media" view, you will see sRGB listed as the color space.

Cheers ... Al
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peterkrogh
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« Reply #4 on: August 11, 2006, 03:51:41 AM »

Dan and Alan are right on the money.

The RAW data in a DNG does not have a color space but the embedded preview does.  When you open the RAW data in a DNG - say by opening the file in Adobe Camera Raw - the data will be opened *into* a colorspace.

The embedded preview is built in sRGB colorspace, but does not actually have a tag in it (this would only confuse matters). Applications that know how to render DNGs know that this preview is actually an sRGB file, and may indicate that the file has that tag. 

Note that setting the colorspace in your camera will not alter the RAW image data.  Rather, it will just put a tag in the file as to what colorspace manufacturer's software will prefer to open the image into.  It will also affect how the JPEG is built if you are shooting JPEGs.

It's a little hard to get at first, but pretty simple once you understand it.
Peter
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MarkP
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« Reply #5 on: August 11, 2006, 06:47:58 PM »

Thanks for the feedback everyone.

In retrospect this now seems obvious, but the Color Profile field in iView
threw me since the File Type and Encoding fields both say RAW
(as of course they should).

Still, it seems odd that DNG would automatically change the color profile
of the embedded jpeg from my camera setting of Adobe RGB (as shown in
iView prior to DNG conversion)to sRGB without documentation or noting
this default behavior.

Clearly, the color profile of an embedded jpeg preview image is technically
irrelevant, but the metadata currently does not distiguish between it and a
jpeg-capture image.

Perhaps on RAW files this field should be left blank???

Mark



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Michael_S
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« Reply #6 on: August 11, 2006, 07:27:17 PM »

It is blank in Adobe Bridge.

--Michael
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AlanDunne
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« Reply #7 on: August 14, 2006, 07:00:08 AM »

 
Note that setting the colorspace in your camera will not alter the RAW image data.  Rather, it will just put a tag in the file as to what colorspace manufacturer's software will prefer to open the image into.  It will also affect how the JPEG is built if you are shooting JPEGs.


Peter, you are (of course) correct about the colorspace only being a metadata tag added into the raw file. One thing that many fail do not account for is that this tag, and the chosen in camera tone curve, can affect the in camera histogram. I once inadvertently ended up with sRGB as the color space for my D200 and I was getting some highlight clipping that I attempted to compensate for through exposure control. Once the images were brought into ACR where my default output color space is Adobe RBG, the images ended up being slightly under exposed.

There are so many thing to account for with digital ...

Cheers ... Alan
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llitten
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« Reply #8 on: July 17, 2007, 05:37:45 AM »

Ok, trying to still wrap my mind around this colorspace and DNG.
I shoot (nikon) raw, and have my camera set to Adobe RGB.

When I ingest the images (imageingester), have them converted to DNG during the ingestion, and view them in bridge they are all tagged with the colorspace left on my camera - aRGB. (note: I even change the colorspace in the workflow options of ACR to another colorspace, and yet the meta tag is still the adobe RGB from the camera)

Question: is this the colorspace then of the JPG files imbedded in the DNG?

I have noticed major color shifts when viewing my images on the web, thus I have learned that I need to change the color setting to sRGB. 

My next question is, if I set this 'smaller' colorspace sRGB on my camera, ingest as described, since I am shooting raw and converting to DNG another raw format, will I still have the ability to access the full color  gamut of adobe RGB later on if I so choose?

Essentially to make my workflow quicker, set the camera to sRGB, edit, play with, manipulate in this colorspace as most of my work is for web, stock photo's, and occasionaly generic walmart type printing.  BUT, if I have an image or two that I really really like, and want to control the output process completly, DO I still have the option of adobe RGB with my DNG files?




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danaltick
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« Reply #9 on: July 17, 2007, 07:48:17 AM »

Litten,

If you're shooting Raw, you can ignore that colorspace tag.  It's for JPEG-from-camera-only.  The Raw DNG data has no assigned colorspace until you import it into Photoshop.  You can tell ACR to assign any of the available working spaces it offers.  The DNG JPEG proofs embedded in the DNG are always sRGB.

Dan
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WindowsXP, ImageIngester Pro, RapidFixer, IVMP 3, ACR4, Photoshop CS4, Controlled Keyword Catalog, Canon EOS50D
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