Xrhrft

I know people use fancy software like Lightroom or Darktable to post-process their RAW files. But what if I don't? What does the file look like, just, y'know, RAW?

There's a tool called dcraw which reads various RAW file types and extracts pixel data from them — it's actually the original code at the very bottom of a lot of open source and even commercial RAW conversion software.

I have a RAW file from my camera, and I've used dcraw in a mode which tells it to create an image using literal, unscaled 16-bit values from the file. Converted to a JPEG for sharing (and scaled to 1200×800), that looks like this:

That's very dark, although if you click to expand, and if your monitor is decent, you can see some hint of something.

Here is the out-of-camera color JPEG rendered from that same RAW file:

(Photo credit: my daughter using my camera, by the way.)

The dcraw program has another mode which converts to a more "useful" JPEG image by stretching the values to a curve where the darks and lights are distributed so they're actually visible. There's still a one-to-one correspondence between photosites on the sensor and pixels in the output. That looks like this:

... obviously more recognizable as an image — but if we zoom in on this (here, so each pixel is actually magnified 10×), we see that it's all... dotty:

That's because the sensor is covered by a color filter array — tiny little colored filters the size of each photosite. Because my camera is a Fujifilm camera, this uses a pattern Fujifilm calls "X-Trans", which looks like this:

There are some details about the particular pattern that are kind of interesting, but overall it's not super-important. Most cameras today use something called a Bayer pattern (which has less green and repeats every 2×2 rather than 6×6). Why more green? The human eye is more sensitive to light in that range, and so using more of the pixels for that allows more detail with less noise.

So, anyway, here's a 1:1 (one pixel in the image is one pixel on the screen) section of the out-of-camera JPEG:

... and here's the same area with the simple grayscale conversion. You can see the stippling from the X-trans pattern:

We can actually take that and colorize the pixels so those corresponding to green in the array are mapped to levels of green instead of gray, red to red, and blue to blue. That gives us:

... or, for the full-sized image:

The green cast is very apparent (and, no surprise because there are 2½× more green pixels than red or blue). If we take this into an image editing program and hit "auto levels", we get something like this:

... which actually isn't half bad, at least from a distance. If you click to get the larger version — which I've scaled down to 1200×800 — you can see that there's lines and other bad artifacts.

So, in reality, conversion programs use more sophisticated algorithms to blend in information from neighbors intelligently, instead of this rough colorizing. And I haven't done anything useful or interesting at all with dynamic range or tone curves or all the things I could have done to the file. This result — basically, a naïvely-colorized RAW file — isn't really the "default" look of the file before processing. It's just one (not so great) interpretation.

All real-world RAW processing programs have their own ideas of a basic default state to apply to a fresh RAW file on load. Which is good, because otherwise we'd have that dark, useless thing at the top of this post.