Tuesday, April 22nd, 2003
What is the best way to adjust a photo? S-Curves!
Use “S-Curve” for Eye-popping Images – Photoshop Tip #6
“Best” is impossible as every image differs considerably, but some ways are better than others. There are three primary ways within Photoshop to adjust photos, so let’s look at them starting with the simplest.
First, Brightness & Contrast. This is a very crude, down and dirty adjustment that is, in fact, a dumbed down version of Levels, so quickly wean yourself off this one because it rarely produces happy results. Next: Levels.
Levels is very good, definitely better than Contrast, and for evaluating a scene (that is, informational purposes) it is perhaps the best measure of your success in capturing the shot (I shoot with my camera’s display set to always show the levels histogram (thanks, Paul) — the best way confirm that you’re not clipping off detail). But, in truth, Levels suffers from a couple of significant drawbacks. First, the gamma on Macs and Windows boxes differ by a few tenths (may not sound like much, but a tenth is a lot). Thus levels adjusted on a Mac often are too dark when viewed on Windows, and those adjusted on Windows are almost always too light (flat) on a Mac. Also, Levels gives you three points, which often, no matter how much tweaking you employ, just doesn’t cut it. So what else is there?
The answer: Curves. Curves is to Levels as Levels is to Brightness & Contrast: Curves is a souped-up Levels control. Plus, Curves can accommodate some fairly drastic color-balance issues by adjusting each channel’s Curve independently (for example, photos shot on overcast days or in shadows can easily be fixed by slightly pulling down the blue curve). But the most useful “trick” you can perform with Curves is a simple “S”-shaped curve. This will pop the contrast and the saturation, giving very pleasing rich blacks and crisp whites.
In this snapshot of the Curves dialog box the blue line is the default — output levels are exactly mapped to input levels. The black (rough) line is a moderate S-curve, the red line a rather pronounced curve. The two adjusted curves bump-up brights, and pull-down the darks (output level greater than input, output level less than input respectively). Note that in the middle areas the curve is nearly linear (flat 1:1) so midtones are barely affected.
Here’s an example where an acceptable photo undergoes dramatic changes (some of you won’t like):
An Example: S-Curve Bird of Paradise
Shoot in a hurry or with white-balance set to auto and often your photos have a strange color cast. In this case, the tell-tale blue of mid-day shadows. Also, even though it’s a decent image there could be more separation between background and foreground: we always want pop, no?
Adjusting Curves takes just a couple of minutes and the results are stellar. Let’s go…
LAYER» NEW ADJUSTMENT LAYER» CURVES…
As the name implies an S-Curve looks like an “S”. Just how much you want to apply is entirely up to you. You are throwing away some data: the more pronounced the S the more you’re discarding.
A shallow S works well for dynamic images, for flatter images push the boundaries.
RGB Curve’s Effect
As you can see this is really quite a difference. It’s similar visual affect is applying saturation, but not really. Mid-tones are smooth, the blacks draw attention to the highlights.
The one problem that hasn’t been addressed is the blue-cast due to the subject being within mid-day shadows. Simply pulling down the blues in the highlights and leaving them to gradually increase in shadows is all it takes for a natural look.
Color-correction within the curves is quite powerful: adjust for flourescents by playing with the Green curve. Indoors and tungsten light? Hit the Red and a bit of the Green, or even increase the mid-point of the Blue.
The highlights are bright, but not ringed in blue. Midtones look warmer — the instant result of changing the mix of red-blue.
Compare this image to the original (click next, then click back to toggle between the two images). You may find this too much, and I wouldn’t disagree — I’d keep tweaking this, it’s a bit aggressively green, but nonetheless this shows the power and perhaps serves as a cautionary tale. Too much is as bad as not enough.
Curves is your all purpose color correction and visual pop tool.