Blinkies, Crunges, the Histogram and HDR

Winking is cute. Winking is sassy. Winking is fun. If you wink with both eyes it’s called a double-barreled wink, or blink. Blinking your eyes takes about 1/100^th of a second – the same time that makes one skier a gold medalist and another only a blink behind, a loser, mere hundredths of a second. And in photography, a recurring case of the blinkies usually isn’t cute, isn’t sassy, and isn’t fun. It’s a blindspot. A blinkie is a highlight that’s just way too bright and washes everything else out. It is a flat bright spot, that ruins the illusion of sculptural form, the subtle tonality needed to create the sense of roundness.

The reverse of a blinkie is what I call the crunge: a super-dark and big shadow region in which there is just dank darkness, no detail, no form. It’s a problem because if you try to print a photo that has a serious crunge then you use up all your printer ink extremely fast, and that burns money. And anyway, it looks like a big flat dark area, kind of boring. Crunges suck. Blinkies suck. Neither one provides you with a wide range of delicate values and hues between absolute white and darkest dark.

In most cases, photos are better when they include a full range of luminosity from very dark to very bright w/many thousands of subtle values between them – the full range is the gold standard of exposure control. To describe it, photographers also use the jargon ‘low key’ (a mainly dark composition), ‘middle key’, and ‘high key’ (a mainly light composition). In each case we don’t want blown-out highlights or shadows. So, how do you avoid the blinkies and the crunges?

First some examples. Maybe you’ve taken a photo like this:

This has serious blinkies. The snow is washed out, and the sky in the upper right is totally gone. 

And here’s the dreaded crunge:

Oof! That hurts my pocketbook just looking at it and thinking about printing it! Here’s the correctly exposed version that has a nice deep dark range and serious, lovely details – a good low-key image:

(If you clicked on the Mt. greylock image you'll see a big problem... wind made my tripod shiver!) (But the exposure is correct and not full of crunge.)

The secret to knowing what to do about blinkies and crunges is first to make sure that you can see them while you’re shooting. To do this, if your camera has a highlight warning function, then turn it on. It’s usually in the camera’s playback menu, or a submenu of the playback menu. So now we’re going to break a cardinal rule and edit on the basis of our image in the camera’s LCD screen. We’re not editing for sharpness, just for over-exposure. If the warning’s on then when you view your image in the camera’s LCD screen, your camera will let you know if any highlights are washed out by blinking sections of the image that are blown-out highlights. It looks like this on the back of my camera:

The screen will blink the highlights from the negative image on the top to the image below – sort of like a strobe light – so that the display shows an immediate exposure problem in a lot of the lights in the image. Thus the highlight alert or highlight warning function can save you a lot of trouble. Use it if you have it.

If you see blinkies then the easiest thing to do is to reshoot the scene, underexposing the image enough that the highlights aren’t too hot – use the +/- button and scroll wheel to adjust the exposure (or whatever controls are available to you to adjust the exposure). You can also experiment and see if you get more blinkies by purposely overexposing the image. Here is the overexposed version of the landscape shown in the LCD screen above (left), next to the stopped-down version (right) which is a very close representation of the snowy, cloudy day at North Pond in Savoy State Forest:

And yes, I took these photos to demonstrate the blinkies for you. Blinkies happen a lot in winter, because exposures are very hard to do when there’s snow. When they sense a lot of light grey tones, most digital cameras try to overcompensate the lights when they are set for automatic exposures (some cameras now have a ‘snow’ or ‘winter’ setting). In this case – a cloudy moment in the middle of a light snowfall, the visual mood was soft and sort of dark, definitely what’s called a ‘middle key’ scene. In real life it didn’t have any bright highlights. The overexposed image almost looks like a bright sunny day in comparison!

But if you have no manual exposure control – no +/- button to mess around with – then what do you do? Try reshooting the scene from a slightly different angle, turning every so slightly away from the highlight. Sometimes this works great. If your camera has spot metering, set it to spot meter so that you can select the exact point where the light meter reads the scene, instead of letting the camera automatically meter an average of the entire scene. You might also be dealing with the kind of camera that has a variety of settings for ‘scenes’ or ‘camera modes.’ Try selecting a different camera mode, for example, using the portrait setting even if you’re making a landscape photo.

Using software you can analyze your photos in many ways, first among them is using your Histogram (gesundheit!) Sounds like a weird allergy medicine doesn’t it? Have a bad case of the blinkies, or a serious bout of crunge? Then take one Histogram and call me in the morning. Some cameras will allow you to check an image’s histogram on the LCD screen. Some cameras won’t. But most image processing software will show you the histogram.

Here’s what the histogram of the good exposure of the scene above looks like in Photoshop:

In GIMP it looks quite similar (see menu Windows -> Dockable Dialogs -> Histogram).

The Histogram is a chart. It shows you how many pixels in your image are at each level of luminance – in other words, how much light and grey and dark you have in your image. It represents the darkest values on the left, and midtones in the middle, and the lightest values (highlights) on the far right. If you have a full tonal range, then you’ll see some pixels across the entire histogram. This chart shows an o.k. distribution, with no bright highlights, and a lot of middle light gray values. Here’s a comparison:

The histogram changes depending on the distribution of luminosity, which is sometimes called value or brightness. The histogram also shows you clues about how you’ve organized your composition – what value and color ranges your image includes. A primarily dark image (called ‘low key’) will have most of the histogram grouped to the left, whereas a mainly light image (called ‘high key’) will have most of the graph grouped to the right. A good distribution in either case will have some height across most of the entire graph.

Now for the fun part: Suppose you have an image that needs a little exposure adjustment – maybe it’s just a tad too light or too dark.

To fix this, use the LEVELS adjustment (In Photoshop, it’s under menu Image -> Adjustments -> Levels; in GIMP it’s menu Colors -> Levels). Here’s what the Levels Control looks like in Photoshop:

See the histogram? You’ll find that you can stretch or compress the histogram by adjusting the input and output levels. Normally I leave the left and right inputs at 0 and 255, and for many landscape images, adjust the centerpoint to somewhere between 0.95 and 0.88 – try it out on one of your own images and you’ll see how your exposures change. If you’d like full details about how this works, then read the HELP file for Photoshop or GIMP. The main point is that you can, if you need to, make exposure adjustments by using the Levels control. As with all adjustments, try to be subtle not crass.

[If you don't need to see a histogram, then in Photoshop you could instead alter the exposure using the menu Image --> Adjustments --> Exposure. This will give you the ability to 'gamma correct' in addition to altering the overall exposure. ]

Of course if you’re starting with a good exposure, you’ll only need a very small adjustment, perhaps no adjustment at all. Finding the best exposures requires that you read the image, on your computer screen and then if you’re going to print it, in the print. Often what looks great onscreen looks too light or too dark in print, even if your screen, file and printer are all calibrated together. So, don’t just look at the histogram… read the image and compare/contrast with the histogram.  

(Exposure Hint: since you know about using Layers, why not make a duplicate layer of your photo, adjust the LEVELS in it, and then use the layer blending options to make subtle adjustments? You could also combine a moderate exposure and an overexposed image to get more detail in the middle grey ranges.)

Finally, there’s one more strategy that can help you avoid the blinkies and the crunges: if possible, always take a set of bracketed exposure of every image. It won’t always be possible… some images are fleeting, moving by far too quickly. But many scenes are relatively still. If you can set your camera to take what it thinks is a good exposure, take it, and then set it to take a few progressively under-exposed and over-exposed images. Then when you’re back at the computer you can upload all five or six exposures, combine the best ones using Layers. You can get many effects by altering the layer controls for opacity/transparency, and blending style (instead of ‘Normal’ try ‘Lighten’ and ‘Darken’). It’s a bit complex but using layers and a variety of bracketed exposures you can build a histogram that shows a wide and full range of luminosity across the entire gamut of light to dark. This is something that you can do with digital photography that’s extremely difficult with wet photography.

And yes, you can do this in an automated way if you want to – it’s called tone-mapping, or, the High Dynamic Range (HDR) image. Wink! Here’s a set of links you can read to learn how to make an HDR image, and why it’s useful:

The ultimate guide to HDR Photography, at Photocritic Blog – probably the best post on the topic, with lots of good links.

Some great HDR images, such as this one of a cathedral, at HDR Crème

Flickr How-to HDR group


That's it! Now go test and find out if you're camera has a highlight warning function, check out the histograms of some of your photos to find some that have great luminosity distributions, and maybe try to make a couple of HDR images... it'll take some practice, but the results can give you a wide array of values across the entire histogram. Here's an example from me: a still life, 'Fantasia'

 

Check out the dark orange shadows underneath Medusa's head -- that's pure, subtle HDR at work.