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The RAW Truth

In this age of easy digital manipulation, raw image formats are considered the standard for what was actually seen by the camera. But a raw file doesn't look like much of anything without your help, both before and after the shutter fires.

A raw image file is a strange beast. It doesn't matter what camera or brand shot it, it's strange. The first thing to realize is that a digital camera sensor is nothing but a collection of individual photosites (pixels), each of which has a simple job to do having little obvious relationship to image making. Each photosite is actually more akin to a thermometer than a camera part. All it does it measure a single value. But rather than recording temperature, it records the amount of light falling on it during the exposure. With millions and millions of these photosites covering the surface of the sensor, it might be tempting to assume that these collectively create the image. But this is only the beginning of the strangeness that is a raw file.

At best, create a black and white image, each photosite recording just a single value. That's easy to get around. Each photosite has a colored filter over it, with neighboring photosite having a different color, arranged in alternate rows of red and green in one row, then green and blue in the next, and so on. No, the real strangeness has to do with the values being recorded, not what color they represent. Each photosite simply counts the number of light photons that falls on it, tallying up its count so long as the shutter remains open. A bright light results in a higher value than a dimmer one. That may sound simple, but it doesn't match the way the human eye records brightness. Human vision is sees successive doubling and halving of brightness as being equal steps, but the sensor records the true value, something known as "linear gamma." In other words, a raw file may contain a lot of data, but not really an image. It needs your help.

There's not really any way to look at a raw image directly. It has to be processed in some fashion to create an image. Take your pick — Lightroom, Photoshop, Skylum Luminar, whatever — but you have to do something to create an image from the mountain of raw data in that file. Open the file and you see a default rendering of the image, but it's still a processed version. Tweak the sliders how you see fit and it may be processed differently, but that doesn't change the basic facts of the situation. Raw files simply aren't images per se without your help.

OK, now that we're all roughly on the same page here with how strange raw files are, it's time to ask the real question. If raw files are so strange and have to be processed before they become usable images in any sense, how can they be the standard for what the camera saw? Raw files are a record of the data as recorded by the sensor's photosites, but you shot the image. And that image ended up looking how you made it look. All digital images are manipulated. They have to be in order to be transformed from a bunch of raw numbers into something that looks like an image at all.

And the camera only sees what you point it at. The sensor only records what you let it while the shutter remains open to form the exposure. Your role in creating that image doesn't start once after you have it on your computer in Lightroom. You're the photographer. The standard for what the camera sees is you. The resulting image is up to you.

That's the raw truth.

Date posted: January 6, 2019


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