Lesson 5 Part I: Why Shoot RAW?

Let's start with the downsides of shooting RAW: post-processing on the computer is absolutely required, which consumes time, automatic post-processing settings in the camera that you may be used to won't apply to the RAW file and will have to be done by hand later, consuming time and effort, and it has something of a learning curve to get used to, requiring time and effort. It's obviously harder to shoot RAW than to shoot JPG.

So why would anyone want to go through the hassle?

The answer is that you get advantages in flexiblity, control, and dynamic range. When you shoot straight to JPG in the camera, you discard a lot of data. JPG stores 8 bits worth of data, values from 0-255, whereas RAW stores 12 bits, values from 0-4095, and in addition, JPG compresses that data in a lossy way, discarding still more information. (Note for the technically advanced: I am deliberately not going into JPG gamma adjustment and real-vs-theoretical RAW ranges at this time to keep things readable.) Certain post-processing decisions made at the time of shooting (such as sharpening), when you can't see what the actual result will be very well, are practically irreversible in the JPG. Applying it later gives you better control over exactly how much sharpening to apply. In addition, there are some quirks to the way information is stored by the camera that can be taken advantage of when shooting RAW, but not so well when shooting JPG that we'll get to later.

For starters, however, let's look at an immediately visible advantage that fits right into the line of this mentoring: 12-bit exposure compensation.

Exercise 5:

You will need to find a scene with relatively even lighting, ideally one with enough light that you don't have to worry about shutter speed too much, but with one area with some detailed object in a moderately dark shadow. You want to avoid a scene with bright highlights for this if possible, but I expect that someone will end up with some highlights that I'll be able to use as an object lesson of the dangers of Exercise 6 down the road. .

If your camera will allow you to shoot both RAW and JPG simultaneously, do so, and Set your camera JPG settings to be as close to neutral as possible (no contrast boosting, no sharpening, auto white balance), and set your metering to be full scene evaluative. Otherwise shoot RAW only, switch over to JPG, and reshoot. If you want to try to follow along with a camera that can't shoot RAW, and compare your images, feel free to do your best. Shoot the scene as
close to the same way with each shot as possible (a tripod would be ideal) using the following settings:

ISO200, evenly exposed
ISO200 one stop underexposed
ISO200 one stop overexposed

ISO400, evenly exposed
ISO400 one stop underexposed
ISO400 one stop overexposed

If your camera supports ISO800 or ISO1600 by analog gain (the easiest way to guess about this since it isn't covered in the manual is to turn off any special or extended ISO modes that might be available, and shoot with whatever is left), also try the following:

ISO800, evenly exposed
ISO800, one stop underexposed
ISO800, one stop overexposed

ISO1600, evenly exposed
ISO1600, one stop underexposed
ISO1600, one stop overexposed

That's a lot of pictures, but we'll be doing minimal processing, so it should go fairly fast.

In your RAW converter, turn off any automatic sensing of values (such as the CS2 RAW import does), using the baseline values for exposure (+0), brightness (usually 50 in ACR), contrast (usually +25 in ACR), etc. In particular, if you are in ACR, make sure you set Shadow and Luminance/Color Smoothing to zero. If you are using the Canon converter, make sure that sharpening and contrast enhancement have been turned off. (We'll be going over all of these values in more detail in the next lesson.) Leave the white balance to the camera default. For the evenly exposed images, import, and then save to a jpg without further processing. For the underexposed images, set the exposure to +1 (brightening them back up to base), import, and save. For the overexposed images, set the exposure to -1, import, and save. If you were able to shoot both JPG and raw, post the unaltered JPG next to each RAW image for a side-by-side comparison, and if you have time, bring the JPG into your preferred image editor, and try to use brightness or exposure compensation alone inside the editor to match what you did in RAW import. No cheating by using other tools, please, since they weren't used on the RAW files. I'm interested in showing just the baseline right now.

If you did everything, This is going to leave you with a whole slew of images to post, which I hope won't be too stressful. At each ISO level, I'd want to see:

[Corrected RAW-Even]  [CamJPG-Even]
[Corrected RAW-Under] [CamJPG-Under] [CamJPG-UnderFixed]
[Corrected RAW-Over]  [CamJPG-Over]  [CamJPG-OverFixed]

Once you have these, have a look at how well the exposure compensation corrected the image in each case, with particular attention to what happened to the detail of the object in the shadow and the amount of noise visible. Keep a particular eye on the difference in noise between one ISO level underexposed, and the next ISO level correctly exposed.

Extra credit:

Take a shot late at night or in an otherwise very dark area at ISO100, three stops underexposed (you'll probably have to switch to manual to do this, and count off stops by doubling your shutter speed). Take the same shot at ISO800 evenly exposed. Post the corrected RAW, uncorrected JPG, and corrected JPG. I expect that the uncorrected JPG will be something close to a black square; this is okay, and I won't be handing out brown ribbons.