Stay ColorSunc

I have a 30” Cinema Display attached to my 17” MacBook Pro, and often when I return to the computer after the screensaver has kicked in, I find that my display has reverted to some default ColorSync setting rather than my calibrated, gamma 2.2 profile. The visual effect is that the screen is brighter and bluer than I’d left it.

You can fix this manually by opening the Displays section of System Preferences. This little ritual has gotten quite old though, and it finally occurred to me to do some Googling. I found this helpful blog entry that suggested the following Terminal entries:

cd /Library/ColorSync/Profiles/Displays

sudo chmod 664 *

(Standard disclaimers apply any time you use the terminal, execute the sudo command, and go outside on a sunny day.)

This didn’t work for me until I also changed the permissions on the Displays directory (and the other profiles in the Profiles directory too for good measure):

cd ../

sudo chmod 664 *

So far so good—I appear to be free from the forces that seek to revert me to -blech- gamma 1.8 land.

Whenever I encounter weirdness with Apple OSs or apps, I try to report them at apple.com/feedback. Who knows if it helps, but almost all the issues I reported about my iPhone became fixes in later firmware revisions.

(Oh, and of course I realize that I could just turn the screensaver off, but I tend to leave it on with password verifications for security reasons.)

Exposing to the Left vs. Exposing to the Right

Google this topic and you will discover a war of sorts, a raging disagreement between those who say you should overexpose digital photography as much as possible, referred to as “exposing to the right” since it piles up the histogram toward the right edge, and those who recommend the opposite: underexpose and create a histogram that is left-leaning.

You must expose to the left because clipping is bad, some say. Overexposure is a non-concept in digital photography. Even when shooting RAW, the rightmost edge of your histogram is a sharp cliff, and it must be avoided at all costs. While you can sometimes recover highlight information from a RAW file, you’ll never get much, and if you miscalculate and clip some highlights, the results will be un-film-like and harsh. Expose to the left and always be safe.

Others purport that you must overexpose your digital photography, i.e. expose to the right, because of how digital sensors work. Unlike film, which has a logarithmic response to light, digital sensors have a linear response. So while film grain is evenly distributed across perceptual values, sensor noise lives predominantly in the shadows. It’s easy to see why when you imagine a linear sensor trying to hold four stops of exposure—if 100% sensor charge is four stops up, then one stop down is half that, or 50%, and one more stop down from there is 25% and one more down is 12.5%. As Jason Rodriguez commented on my dynamic range post, fully half your chip’s sensitivity is devoted to the brightest stop you can hold. Each stop you drop from there doubles your noise. So to maximize your signal to noise ratio and get the cleanest image, you must overexpose as much as you can, to distribute your image across the chip’s least-noisy sensitivity range.

Like the raging war between the half-black, half white aliens in Star Trek episode 70 (oh yeah, I went there), this is a non-argument. Both philosophies are 100% correct, and should be in play in the digital photographer’s mind when deciding on an exposure.

It’s so simple to state the combination of these two philosophies that renders both extremes silly: You should expose as bright an image as you can without clipping.

Man, that’s so much easier. I don’t know why people put so much effort into the debate.

Let’s look at some images. Here are some trucks at f/11, 1/500:

(click images for larger size)

Here’s that same view at f/8, 1/250 (for a total of two stops brighter):

The first image is a about a stop underexposed, although it does have small highlights that are just barely being held. The second image is clearly blown-out, and appears clipped in the highlights, but holds nice shadow detail.

But these images are raw, so we have some flexibility. Here they are again, color corrected in Lightroom into a similar look:

They almost match, but if you look closely at the overexposed image you can see that, while Lightroom was able to recover a surprising mount of detail in the highlights, the backs of the white trailers are still a flat, featureless white, with abrupt, cyan-to-white transitions in shading. Almost worse are the highlights in the clouds, which reveal Lightroom’s desperation.

Meanwhile, in the shadows, the underexposed image is a bit noisy, whereas the overexposed image is cleaner.

But the difference is not very noticeable. In this case, it seems the advantage goes to the underexposed image. Had I opened up a stop I could have reduced noise in the grays by half, but I’d be missing some highlight detail on the foreground truck. My fear of blowing out caused me to expose to the left, with happy results.

And now the counterexample: Another pair of images two stops apart:

Another attempt to make them match:

And while in the second image one could say that the clouds are a bit clipped, and the sky a bit low saturation, this is hardly as noticeable as the noise in the shadows of the underexposed image:

So our second image would seem to indicate a victory for exposing to the right.

You’re probably way ahead of me on the conclusion: You cannot apply a blanket philosophy of underexposure nor of overexposure to digital photography. Instead, you must learn your camera’s nuances and seek the correct exposure for the scene—which will almost always be as richly exposed as possible without clipping. Sometimes the resultant histogram will be left-leaning, and sometimes it will be piled up to the right. Make the shot, not the histogram.

Nuke 5.0 Released

Now featuring: Good taste.

What was once the fugliest compositing app on the planet is now a joy to behold.

There are other fancy new features too, and the same speed and power that set Nuke apart from the moment it was released. But the new UI should provide a nice, smooth on-ramp for Shake users interested in giving it a go.

EDIT: Heh, no wonder I like it so much, you can't tell where this screenshot stops and my (old) blog layout starts!

Digital Cinema Dynamic Range, Short Version

Here's another way to put it:

Shooting with RED One rated at its native sensitivity and monitoring Rec709, if you put 18% gray at 45% IRE, you'll capture 2 stops over 18% gray, plus some headroom.

If you underexpose from there by 1 stop, you'll capture 3 stops over 18% gray, plus a little headroom.

Underexpose by 2 stops, you get 4 stops over 18% gray, plus headroom.

Want to match Panalog? Underexpose by 3 stops for 5 stops over 18% gray, plus headroom.

Want to match a hypothetical "perfect" film stock? Underexpose by 4 stops to match the Cineon spec's 6 stops over 18% gray... you guessed it, plus some headroom.

And then put the results into your grading system and see if the noise levels on your gray card are acceptable.

This is what I'd do if I had a RED One, a pretty girl, and a window!

EDIT 080223: I added the italic text at the top in response to David Mullen's post on the reduser.net thread that's been running parallel with these posts.