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Shooting JPEG


A few quick observations about figuring out how to set JPEGs

Original: 12/13/2011

For years I've been fighting the JPEG battle. No, I don't have any particular dislike of JPEG and if you're looking for convenience pictures (as opposed to best possible images) there's absolutely nothing wrong with using JPEG. I use it from time to time myself.

The problem with JPEG is that it is destructive and it is final. On a 12mp camera, for example, there should be at least 18MB of data coming off the sensor. A typical camera will throw away about two-thirds of that when creating a JPEG. Worse still, there's an implied 54MB of data (due to the Bayer demosaic), and the final image will have about 10% of that. The destructive part is clearly destructive. The question is thus: what is being destroyed?

Well, it depends upon what the settings are and whether you optimized your exposure. I'm not going to write about that last bit (optimizing exposure), because it's a different problem and one for another article. Today's essay is about optimized JPEG settings.

Let me state a bias right up front: I believe it is easier to add effects into neutral data than it is to take effects out of "pushed" data. So if you're willing to do any post processing on JPEGs, I'd highly implore you to do two things: (1) set optimal exposure; and (2) select camera settings that don't push the underlying data from neutrality. What's that last part mean?

White balance is an easy one to understand in that respect. In simplistic terms white balance is created in a JPEG by rotating the red and blue channel values around green. In "red" (warm) light we boost blue and lower red. In "blue" (cool) light we boost red and lower blue. If we set white balance perfectly, we get just the right boost/reduction in those channels. If we set white balance wrong, one of those channels will be higher than it should be, the other lower. Altering that balance after the fact is a more-difficult-than-average post processing chore with JPEGs, partly because you've only got eight bits and moving channels much will usually promote noise or blockiness in the channel being boosted. (What's blockiness? You have very few bits recording shadow detail in a channel. There's not a lot of definition in 8-bit shadows. So if you start to move those values up, they don't quite look right. Consider a value fully recorded in two bits [that's four possible values]. If we move that up to middle tones where we expect lots of definition and micro contrast in the details, we no longer have it: those four values don't provide much detail, and now that's in the area we most look at for luminance definition.)

If you use Auto white balance, which is the default on virtually every digital camera made, you'll tend to get decent white balance in outdoors mid-day sunlight, and not so good the further you get from those things (outdoors, mid-day, sun). In digital cameras I've tested over the years, the "midpoint" of the white balance rotation has typically ranged from about 4100K to 5600K (outdoor daylight is traditionally referred to as 5400K because that's what the US standardized on back in the 1920's, but it can vary with latitude, time of year, and altitude). The further you get from that value, the more the camera is driving the red and blue channels in opposition. So, first rule of thumb for JPEG shooters: learn how to take control of the white balance and make sure that you're not getting overly warm or overly cool data in your images (unless, of course, that's what you're trying to achieve, which is yet another story for another day).

Camera makers set other defaults that have impacts on our JPEGs. The short list to pay attention to is color, saturation, contrast, noise reduction, and sharpening. Here's the thing: virtually no camera I've used has a default that matches what I'd set. Let's explore each of those separately:

  • Color: color is a bit like white balance, but here it's much more nuanced. In Nikon's EXPEED world we use "Picture Controls" to control basic color. The Nikon default of Standard is actually a slight color shift; if you want no color shift you should use Neutral. Many of the complaints (or compliments) about how a camera handles skin tones or other common colors such as sky or grass, have to do with those shifts. Film was not neutral. Far from it. Slide film was oversaturated, and films like Velvia had magenta shifts in the blues. Kodachrome was notorious for strong color shifts. Print films themselves weren't overly biased in color, but the automated print machine your one-hour photo processor used would often crank in saturation and other color shifts. Why was film not neutral? Because viscerally we respond to contrast, and color is a form of changing perceptual contrast. For some reason, we Westerners tend to like warm skin tones (maybe we've been out in the sun too long). The way most film, and now digital camera, makers handle color changes is usually via forms of hue shift. The classic Fujifilm look that many like is a double hue shift: reds shift towards yellow and greens also shift towards yellow (yellow is between green and red). My problem with that as a landscape photographer is that some blues tended to shift with the green, which made skies cyan (the opposite of the Velvia sky, which went the other way). So be sure to look at the basic color shifts that are available to you in JPEG shooting. Again, in Nikon EXPEED terms, we have Standard, Landscape, Vivid, Portrait, and Neutral, all of which have different sometimes subtle sometimes extreme shifts in certain colors. Landscape very well may be what you want for some landscapes, but it likely isn't what you want when people are in the picture. Experiment and find your desired choice for common situations. Other cameras use different terminology, but have similar choices. My Olympus Pen has i-Enhance, Vivid, Natural, Muted, and Portrait, for example (plus Pop Art and Custom choices). You need to know what those choices do, and choose the right one for what you're shooting.
  • Saturation: Saturation is something you need to be careful of with JPEGs. Yes, we tend to want saturated color, but too much saturation means you'll have a hard time changing something after the fact. Again, adding saturation is far easier than removing it after the fact (Dan Margulis was demonstrating things at Photoshop World this year that tend to contradict that, though you'd need his tools to follow his recipes). Moreover, saturation affects all colors. Most people actually don't want saturation, but more vibrance (color differentiation) with a bit of saturation. You'll normally need to post process that in.
  • Contrast: Contrast is another of those easy to add but tough to remove settings. Dull, flat images don't look as great as high contrast ones, but if you miss contrast and need to reset it after the fact, you may be in another of those missing data situations with JPEGs. But if you have low contrast JPEGs, you can usually add contrast in, and you can do so selectively (add it in shadows and/or highlights, but not mid-tones, or vice-versa).
  • Noise reduction and sharpening: We all hate workflow. We hate it so much that we're willing to dial in lots of camera controls in our JPEGs and hope for the best. Be very careful about these two things, though, especially since they interact. If you dial up lots of noise reduction and sharpening, you get that plastic-fantastic look to edges and detail: they just don't look real, they look almost as if they've been painted instead of photographed. With this particular pairing of settings, you need to experiment based upon ISO. What works at ISO 100 won't at ISO 400. What works at ISO 400 won't at ISO 1600. And so on. In other words, you very much need to alter your settings here to each individual ISO.

So how do you get to a set of JPEG settings you like?

  1. Remove a variable. Shoot your tests at base ISO and sharpening off with a known value of lighting and a White Balance that matches. Sunlight mid-day is okay if that's the only way you can get close to removing White Balance as an issue. Basically, we don't want White Balance shifts to impact our testing.
  2. See if you can find neutral. On a Nikon with Picture Controls, that's easy: choose Neutral and choose a Contrast of 0 (low to mid contrast scenes) or -1 (high contrast scenes) for it. For other cameras you might have to read reviews, the manual, or consult forum experts to figure out what this is, but usually there's something called Natural or some other name that suggests that it isn't spiced up. That's what we want. Now shoot some test subjects: people, landscapes, flowers, whatever you normally shoot.
  3. Examine your neutral results on a calibrated computer monitor with the right Color Space. They're likely going to look a bit flat and not dynamic. That's okay. We want to know that we're capturing things pretty much as they are, without enhanced contrast or coloration.
  4. One at a time, season to taste. In Step three you noticed something about your images you didn't like (probably; if not, you're already done ;~). For example, there's not a lot of contrast. Great. Go back out and shoot and and try different contrast boosts (or drops if you thought there was too much). As in Step 3, examine the results and pick one. Once you have contrast to your liking, do the same thing with color shifts and saturation, in that order. You may at some point find that your contrast is now a bit high, so back it off one setting, if necessary. Iterate if you have to until you're satisfied that you've found the "look" you like.
  5. Time to figure out Noise Reduction and Sharpening. Boost your ISO to the max you typically use. Reshoot your test subjects with the settings you settled on in Step 4 (you'll probably now need to be indoors with known light) with various NR settings in play. Examine them carefully to find the one that has just a hint of (hopefully just luminance) noise in it. Once you've found that, start boosting Sharpening until you've got the result you want. With some systems, unfortunately, you may have to keep tweaking both the Noise Reduction and Sharpening simultaneously due to interactions. Fortunately with Nikon's Picture Controls, that doesn't tend to be the case. What you don't want to do is set Noise Reduction and Sharpening both so high that they start to interact and they make the plastic-fantastic look on all edges. You'd rather have a hint of noisy, but sharp edges. Trust me on that one.

At this point, you should have something that's "your standard" for JPEG settings, not what the camera maker thinks you'll like. Your standard, by the way, should be just that: your basic setting for most situations. There will be time when you want to exaggerate or emphasize something, but you should be dialing in that exaggeration from your standard, not from some random starting point.

Those that shoot raw will note that some of the workflow here mimics what many of us do with raw conversions: exposure right first, then white balance (then maybe an exposure tweak), then contrast, then color, and finally noise reduction followed by sharpening.

 

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