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Raw Conversion: Better Never Than Late

April 24, 2008

And can we please stop calling them raw converters?

Most Digital SLRs, the Leica M8 rangefinder, and a few mid-priced non-SLRs (Canon G9, Leica D-Lux 3/Panasonic DMC-LX2, Sigma DP1, Ricoh GX100) can capture raw data, as well as JPEGs. A raw capture is taken straight from the sensor, so, unlike a JPEG, it has to be processed before you get a useful image. Raw captures are stored in files that end in .NEF, .CR2, .RAW, .DNG, and so on.

Operationally, the main difference between raw and JPEG is that with raw you process the data on your computer to form the image, not in the camera using preset controls (white balance, saturation, etc.). That gives you a lot more flexibility, since you can tailor the processing to the specific image, instead of having to make decisions before you've pressed the shutter. Processing is interactive—you can immediately see the effects of various adjustments.

Rather than say that a raw capture has to be processed with a computer, as though it's a disadvantage, it's better to say that it can be processed, which is an advantage. Or, to say it another way, if you edit images on a computer anyway, you're better off editing a raw capture rather than a JPEG, just as a baker can bake a better cake from raw ingredients than from an all-in-one cake mix.

(It used to be true that processing raw captures was more complex than processing JPEGs but, with modern raw processors, this is no longer the case. With some applications like Lightroom, Aperture, and Adobe Camera Raw, there's no difference at all other than file size and, of course, the results you can achieve.)

Michael Reichmann of The Luminous Landscape web site has written an excellent article that shows why editing a raw is better than editing a JPEG. You'll also want to read Thom Hogan's Quick & Dirty Guide to RAW.

Unfortunately, the most common term used to describe raw processing is "raw conversion", which implies that the purpose is to convert the raw data to a more accessible format, typically JPEG or TIFF. But as soon as you've converted you've baked in the adjustments you've made (color balance, saturation, sharpening, contrast, brightness, etc.). You may have benefited from the advantages of shooting raw while processing initially, but once you have a JPEG or a TIFF those advantages are gone for good, unless you go all the way back to the original raw and start completely over.

Raw conversion isn't the purpose of raw processing—it's an unnecessary evil. It's better not to convert at all, as I will explain.

It's useful to classify raw processors into three types, two converting and one non-converting. I'll add in-camera processing for completeness. They're listed from worst to best.

Type Comments When Appropriate
No raw Shooting JPEG rather than raw. In-camera processing based on camera settings prior to exposure. Computer processing still possible on already-baked image. When raw-processing is too time-consuming or unwarranted, file size is an issue, or the camera doesn't shoot raw.
Early Conversion Some camera-manufacturer-supplied Photoshop plugins work this way. If, when you first open a raw file you're presented with an initial panel with only a few adjustments (maybe white balance, contrast, brightness and maybe one or two others), and then the image shows up in the full-blown editor, you have early conversion. If there is no initial panel, or there is but it offers extensive editing, then you have late conversion (see next row). Should never be necessary. If you think you're getting early conversion, use a different raw processor or, if you're using Photoshop, switch to Adobe Camera Raw.
Late Conversion You do nearly all your editing, including cropping, sharpening, and maybe even spotting and localized adjustments, entirely in the raw processor, working on the full 16-bit image (or as many bits as the camera produces).

Many advanced raw-conversion applications supplied by camera manufacturers (as opposed to plugins; see previous row) work this way. So do most advanced third-party applications like Capture One, BreezeBrowserPro, and Adobe Photoshop with Adobe Camera Raw as the raw-processing plugin (if you finish by editing in Photoshop). Apple's iPhoto works this way, too.

No difference in the quality of conversion compared to non-converting (see next type), but you have to make sure you've taken full advantage of the raw form before you finish. Subsequent editing must be on the saved image (TIFF or PSD, usually) or on the original raw; no way to pick up from where you left off and still stay in the raw domain.
Non-Converting Parametric Raw file isn't modified (non-destructive editing), and neither are the changes saved as an image. Instead, your edit parameters are kept in a history list, and they're reapplied each time the image is rendered. A JPEG preview may be kept automatically to speed up viewing, but printing and exporting are from the raw image as modified by the parameters. Various formats (TIFF, JPEG, PSD, DNG) can be exported, but they aren't used for editing.

Offered by Apple Aperture, Adobe Lightroom, Nikon Capture NX, Adobe Camera Raw (if you don't go on to edit in Photoshop), Bibble (I'm told), and maybe a few others. (Most such apps provide parameterized processing for non-raw images, too, but this article is only about raw processing.)

Convenient because you don't have to store and name different versions of derivative files, you can go back and tweak the editing at any time, and you can easily and efficiently keep multiple versions of the same image.

The most common industry term for what I call non-converting parametric raw processing is non-destructive, but I don't like that term because early- and late-converters (rows 2 and 3 in the table) are also non-desctructive, in the sense that the raw file isn't modified.

Peter Krogh has written an excellent white paper, Non-Destructive Imaging: An Evolution of Rendering Technology, that explains what parametric editing is and how it works.

The difference between parameterized and non-parameterized raw processing is the same as the difference between keeping a word-processing document file or just keeping a PDF that you've rendered. If you want to make edits later, it's much easier if you can work from the original document instead of only from the already-formatted image.

Even with a parameterized raw processor, you can't stay parameterized forever for every image. If you have to go to Photoshop, you'll have to save your work as a derivative TIFF or PSD. Then it's fully baked and any further processing will be from the derivative. (Although if you're careful you can keep the layers, which gives you some benefits of parameterization.)

So, the goal is to stay raw as long as possible. If you have a non-parameterized raw processor, do as much as possible in the raw domain before you have to save your work and exit the program. With a parameterized raw processor, you can stop editing, exit the program, and pick up where you left off (perhaps rolling back some changes) at any time.

What you want to avoid as long as possible is raw conversion. And better never than late.

Blog Archives

Photography Articles

Raw Conversion: Better Never Than Late April 24, 2008

Scanning in India by Way of California With ScanCafe February 15, 2008

How To Back Up Your Personal Computer January 30, 2008

Every Camera I've Ever Owned January 25, 2008

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Lessons Learned From My Memory Problem December 20, 2007

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"The Luminous Landscape" Teaches Me to Print August 4, 2007

Creating a Google Photo Map (Revised) June 26, 2007

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Trying Out Infrared January 20, 2007

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