Color Space - sRGB or Adobe RGB

Started Jul 23, 2010 | Discussions thread
John King
John King Forum Pro • Posts: 14,941
Another vote for Adobe RGB

Gidday Jimmy

Jimmy Lai wrote:

Color Space – sRGB or Adobe RGB – which do you prefer? And Why? sRGB seems to be the default setting on all the cameras.

Reading the various replies to your question, all contain good info and suggestions.

Since my elbow is feeling better than it has been for several weeks (I hurt it rather badly ... ), I will expand on what I, and others, have said.

A RAW file is not an image file. This cannot be stressed highly enough. It is a data container that stores the data about the camera, its sensor, the Colour Filter Array (CFA), all the EXIF info about the lens, f-stop, FL, shutter speed, etc - this is all stored as metadata (metadata = data about data). The RAW file also contains the actual data values recorded by each and every pixel on the sensor for that exposure.

None of this data is interpreted by the camera in any way; it is just written out to the memory card as the raw data - hence the name "RAW".The fact that all this data about the image is stored separately allows a program such as Photoshop to then translate this into an image, which is then saved as an image file in the chosen format. PS and your computer have a whole lot of processing 'grunt' that a camera cannot possibly have, regardless of make or model. Even so, I am constantly amazed at the performance of modern cameras, just in processing this amount of data along the data path to the card ... regardless of in-built buffering.

Every time you change a colour profile of an image file (JPEG, TIFF, PSD, etc, etc - there are literally hundreds of different image file formats ... ), it involves re-mapping one colour number to another colour number. Most likely, the new colour number will already be used by an existing colour in that image. This means that where you originally had two colours, you now have only one. You have lost data! This also applies to every other edit you do to an image file .

With a JPEG, you have far less data to start with, so any data loss is likely to degrade the image. The simple fact of the matter is that when you are working on a file that is not, and never has been, compressed using a lossy algorithm, you have far more data to start with (All JPEGs and some RAW files ... not Olympus RAW files, however).

When a 12 bit RAW file is mapped into a 16 bit colour space, there is far more latitude for editing before one combines multiple colours into one colour. Also, some processing of the RAW file is completely free of data loss (e.g. setting the WB - a RAW file does not have a WB until one is assigned to it; or assigning a colour space, ditto). If a RAW file is mapped into an 8 bit colour space, data will be lost. This will impact some photographs more than others, but will always occur.

For reference, the following bit depths allow for the numbers of colours for each R-G-B channel:

  • 8 bit = 2^8 = 256 colours per channel (sometimes referred to as "24 bit colour")

  • 12 bit = 2^12 = 4,096 colours per channel

  • 16 bit = 2^16 = 65,536 colours per channel (sometimes referred to as "48 bit colour")

It is also possible to easily process one RAW file in multiple ways and then combine the results using layers.

Just as one example of all this: When I have scanned film using my film scanner, the 16 bit, 2700 dpi scans look better than the 8 bit, 5400 dpi at first glance ... It appears that the colour depth is even more important than the resolution. I usually use 16 bit, 5400 dpi however, as this gives better results than either of the other two ... . The film scanner is a true colour scanner, having separate R-G-B scan heads. It also comes with excellent software. This latter is where cheaper scanners often fall down badly.

My uploaded JPEGs start out as aRGB SHQ/LSF OoC JPEGs (I shoot RAW + JPEG), except for my E-30 where they are LF JPEGs.

I select the images I want in Bridge. They are then sent to a batch PS action that applies a standard USM of 30%, 2.0 pixel radius, converts to sRGB, resized to 1024 x 768 (using the PS Bicubic Sharper algorithm), then saves with a filename suffix of "_Ew" so that I know what has been done to it in my upload folder. I then upload all images using the Windows XP Uploader, changing all the defaults in that program when I do so ... I have never discovered where the XP Uploader hides its default values (anyone know?).

Hope this is of some further benefit to you ... ;).

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Regards, john from Melbourne, Australia.
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