Digital Negative archival photo format

On 28-09-2004 15:36:58, Kevin van Haaren wrote:

>Just in time for Charles Maurer's article on digital photography Adobe has
>released a new digital file format. Called Digital Negative (DNG), it's a
>publicly available (and free) specification intended to be an archival
>format for the raw format. They have a free converter to convert raw
>images from 65 cameras. There's an update for PhotoShop CS adding support
>for DNG and the raw files from those cameras too.

What puzzles me is why anyone would want to use a 'raw' format when a lossless image
format (TIFF) is already available, and supported by everyone. The only thing you might
want to add to the TIFF spec is EXIF image data.

Harro de Jong

At 10:14 am -0700 30/9/04, hjongtriview.nl wrote:
>On 28-09-2004 15:36:58, Kevin van Haaren wrote:
>
>>Just in time for Charles Maurer's article on digital photography Adobe has
>>released a new digital file format. Called Digital Negative (DNG), it's a
>>publicly available (and free) specification intended to be an archival
>>format for the raw format. They have a free converter to convert raw
>>images from 65 cameras. There's an update for PhotoShop CS adding support
>>for DNG and the raw files from those cameras too.
>
>What puzzles me is why anyone would want to use a 'raw' format when
>a lossless image
>format (TIFF) is already available, and supported by everyone. The
>only thing you might
>want to add to the TIFF spec is EXIF image data.

Adobe's proposed DNG format is an extension of the TIFF format.

What's special about RAW format files is that they are the actual
output from the pixels of the camera sensors, not a processed version
to make up a nice array for RGB pixels.

Since destop computers have a lot more power and time to do the
conversion from the sensor data to colour image data than the
processor in a digital camera, professional photographers using
digital cameras nearly always save RAW format files and do the
conversion at the computer.

Unfortunately, there isn't one RAW format, but well over 50.
Photoshop supports lots of them, but I'm sure Adobe would like it if
Camera manufacturers started to standardise a little!

--
Paul Durrant

Harro de Jong wrote:

What puzzles me is why anyone would want to use a 'raw' format when a lossless image format (TIFF) is already available, and supported by everyone. The only thing you might want to add to the TIFF spec is EXIF image data.

While TIFF may be lossless in that it does not degrade images from save to save, it is not the same as a RAW file. RAW data is that, transferred directly from the camera's CCD into a file, without any additional processing, sharpening, white-balance adjustments, etc. TIFF files, while not using lossless compression, still involve interpolation and processing.

Some photographers, especially professionals, prefer to use the RAW file and do their own processing in Photoshop, since they have finer control than if they let the camera's own automated software do it:

<http://www.photo.net/learn/raw/>

Right now, there is no standard RAW file format, so each camera manufacturer has its own way (or sometimes several ways) of saving RAW data in a file, making it necessary for Adobe or other parties to update plugins that let you read them into Photoshop, for example. Adobe's DNG is an attempt to create a standard RAW file format that all camera manufacturers can use, thus simplifying file editing and long-term archiving.

In a way, it's similar to what Adobe did with PostScript. Before that page-description language, every program or OS had to have different printer drivers for every printer -- WordPerfect had legions of developers working on printer drivers. With a single PostScript standard, printing became a lot easier, and desktop publishing became possible.

This won't be that much of a revolution, but it's a good step.

-- Derek K. Miller dkmillerpobox.com http://www.penmachine.com

At 10:14 AM -0700 9/30/04, hjongtriview.nl wrote:
>What puzzles me is why anyone would want to use a 'raw' format when
>a lossless image
>format (TIFF) is already available, and supported by everyone. The
>only thing you might

Adobe explains this in its DNG overview:
<http://www.adobe.com/products/dng/pdfs/dng_primer.pdf>. (BTW, the
DNG format is an extension of the TIFF 6.0 format.)

The main reason has to do with the way most digital cameras work. A
5 megapixel camera has 5 million light sensors, but each records only
a single channel (either red, green, or blue). To create a
complete image, software in the camera or on your computer, has to
fill in the rest of the data.

A RAW file represents the data directly from the image sensor, and is
the most basic representation of what the camera recorded. A TIFF
file is derived from this data, and some information is lost in the
conversion. (The TIFF/JPEG image typically uses 8-bits per channel,
while the image sensor usually captures more than that; also, there
is some sharpening, etc. done during the conversion.)

--
Larry Rosenstein
lsralum.mit.edu