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Some RAW Files Aren't so Raw After All

I see you've decided to take some time out from shooting RAW files to read this week's Phototip article.

As long as we're on the subject, there are a couple of file types very similar to camera raw files that aren't really the same thing at all.

Long ago, in the days when you would be laughed at if you said you were going to buy a digital camera, Thomas Knoll invented the PSD format as the native file format for Photoshop. It's still with us today of course and has become one of the most popular image file formats of all time. A PSD file contains the bitmapped data for the image layers themselves along with some additional header information used by Photoshop to understand the file contents.

Around about the same time, they also created a variant of PSD that lacked the header information. This simplified version was used for importing and exporting image data in ways that aren't terribly relevant today, and such files are now uncommon. Photoshop does still support saving files in this format. They're called, confusingly enough, RAW files. Yes, the same name as is now used as the generic name for camera raw files, yet an entirely different thing.

This kind of RAW file only supports 8-bits per channel. If you have an 8-bit image, you can select make one by selecting "Photoshop RAW" from the Format drop-down list in the "Save As" dialog of the File menu. The only reason to do so though would be out of idle curiosity since you can't do much with one once saved.

Another interesting but less than practical file format that is often confused with camera raw goes by the name "NEF," just like what Nikon uses for their proprietary raw capture format. Such files are even made by Nikon software and the acronym still stands for "Nikon Electronic Format," yet they're not really the same thing. Confused yet?

The NEF format is a somewhat malleable one when it comes to the actual image content. It always contains a set of instructions that are applied when the data is converted to a usable image, but the image data itself may not be just a single channel as it is coming out of your camera. Nikon Scan can also save images as NEF. As with a camera raw file, the data is still in a linear gamma space and consists of a raw dump from the scanner. Unlike a camera raw file though, such images already contain individual red, green and blue channels. A scanner works differently than a digital camera and uses LED's in each color rather than the Bayer mosaic.

For this reason, there is no space saved by using scanner raw over any other RGB format. The real problem with scanner raw though is that there isn't much you can do with the format. In theory, you could come back and reprocess them somehow later, but there's little point so long as you still have the slide. Camera raw files become your digital negative. Generally, you can't go back and retake a picture, so the raw file becomes your master image file, the file you return to whenever Adobe, Nikon or whoever releases a new version of their conversion software and you want to see if you can eek some additional detail out of it. In the case of a slide though, Nikon may release new firmware for their scanners, but they also come out with new scanner models periodically. You can return to the slide itself when you bring home your new, higher resolution scanner. You don't need a scanner raw file from your old scanner. I save scanned images as 16-bit Photoshop PSD files. Now that I haven't shot film in several years, I'm unlikely to upgrade my trusty Nikon Coolscan 4000 ED anytime soon, but if I do, I'll simply rescan those I want to invest more time in.

The problem with file formats is that computers have been creating files for a lot of years now, and for a lot of different purposes. It was inevitable that the same or similar names would eventually be used for different purposes. Welcome to the digital age.


Date posted: March 13, 2005

 

Copyright © 2005 Bob Johnson, Earthbound Light - all rights reserved.
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