Raw Conversion: Better Never Than Late

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.

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.

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