Intricate Curves
Steve Weinrebe
A Curves adjustment layer is a powerful tool for tonal and color correction. Curves can also be a chameleon-like tool, adapting to the nature of whatever problem we may have in Photoshop. Here is a way to bring out subtle changes in a tight portion of an image, in this case - wood grain. Because we can adjust small portions of the tonal range of a photograph using curves, we make a barely visible tonal variation in this musical instrument glow with depth.Last tutorial I demonstrated a method to get curves to obey a mere whim, the need to see what was happening in a very light or very dark image. This time let's look at how Curves can work in subtle ways, on very isolated portions of an image's tonal range. Because this method will shift the color somewhat, we'll use the Luminosity blending mode to apply curves to just the tonal values of the image. Along the way we will use Layer Masks to apply two different curves to specific areas of the image.
Apply a Curves adjustment layer to bring out the wood grain
Some subjects in a photograph have very subtle shading or variations in tone. Sometimes they are brought out by lighting or shadow, and sometimes those tones need help to be visible. When lighting this musical instrument (a mountain dulcimer) I tried a spotlight which by its nature would bring out the contrast in the wood. But the light was too harsh. So I switched to a diffuse light which looked better for the overall look I was going for, but the wood grain's variation in tones flattened out. In Photoshop, I can use a Curves adjustment layer to bring those tones back.
Step 1:
From the adjustment layer menu at the bottom of the Levels palette (the little half-moon icon) choose Curves.
After choosing Curves in the adjustment layer menu, the Curves adjustment layer will appear in your Layers palette and the Curves dialog will open with, no - not a curve, a straight line known as a "point curve". In Camera Raw and Lightroom you will see the point curve option, as opposed to the "parametric curve." The difference is that the "parametric curve" allows you to influence regions of tone, shadows, midtones, and so forth. The "point curve" allows you to apply anchor points to any part of the curve and by moving those anchor points up or down, adjust the tone at that tonal point to be lighter or darker. Of course areas around that point get adjusted with it, creating a curved line (a good thing or the image becomes posterized with sharp bands of tone). With curves, less is more, so use a light hand!
Step 2:
Add anchor points to the Curve by Command (Mac), or Control (Windows), clicking in the image. The cursor becomes an eyedropper when hovering over the image and by Command/Control clicking at any given point in the image, an anchor point appears at that tone in the Curve. In this image, since we want to bring out the wood grain, I will Command/Control click on lighter and darker areas of the grain in the area of the photograph where the wood grain is most pronounced. In the next four figures you can see, by the arrows, which part of the wood grain corresponded with which point on the Curve.
First anchor point.
Second anchor point.
Third anchor point.
Fourth anchor point.
Adjust the anchor points to bring out contrast in the grain
Step 3:
Now by nudging each anchor point up or down, the tone in the image can be lightened or darkened just at that point in the tone curve (in other words the tonal range). The lighter portions of the wood grain, represented by the anchor points higher up in the curve, become lighter; and the darker portions of the wood grain, represented by anchor points lower down on the curve, become darker. Of course anytime we make the lights lighter and the darks darker we are increasing contrast. (Note that I kept the two darker and two lighter anchor points at different amounts of adjustment, specifically trying to achieve as much differentiation in the tones of the wood grain as possible.)
Apply the curve adjustment in Luminosity mode
Our Curves adjustment has caused an increase in the saturation of the image by lightening and darkening the color channels. But we have this wonderful feature called "Blending Modes" that allows us to apply the Curves to the Luminosity values of the image only.
Step 4:
Change the blending mode of the Curves adjustment layer to Luminosity, by clicking on the blending mode drop-down menu at the top of the Layers palette and choosing Luminosity (all the way at the bottom).
By applying the Curves adjustment layer in Luminosity blending mode, the color of the wood returns to normal, but the wood grain still has the added contrast applied by the Curves layer.
Add a Layer Mask to hide the center fretboard
Because the center of the instrument, the fretboard, is made of a different, darker, type of wood, let's use a layer mask to hide that portion of our first curve, so that we can make a separate Curves adjustment layer for that portion only.
Step 5:
First we'll use a Selection tool to make a selection around the center fretboard. In this case I used the Polygonal Lasso which is and especially easy selection tool to use when we have shapes to select that have straight lines.
Step 6:
With the Curves adjustment layer the active (highlighted) layer, by choosing the menu item Edit > Fill, and filling the selection with black, that portion of the adjustment layer's mask fills with black, hiding that portion of the adjustment.
Remember, with layer masks that are associated with adjustment layers, the adjustment applies only the white portion of the layer mask. The adjustment will not apply to any portion of the mask that is filled with black. (Tip: the adjustment would only be partially applied if the mask had a portion filled with gray).
Step 7:
Add a new adjustment layer for the center portion of the image.
Because a portion of the canvas is selected, the adjustment layer's mask automatically includes that selected area as white, and fills the unselected areas with black; applying the adjustment only to the white, or previously selected, areas.
Step 8:
Now I'll repeat the steps on the center wood, which has different tones than the lighter wood around it. First I Command/Control click on a lighter portion of the wood to add an anchor point on the curve at that tonal value.
Then I Command/Control click on the darker portion of the wood to add an anchor point at that tonal value.
Then I drag the lighter tone anchor point (higher up the curve) upward, and drag the darker tone anchor point (lower down the curve) downward. The problem I encountered at this juncture was that the upper part of the curve became too bright, from the tail-wags-the-dog effect that can happen when one part of curve is moved carrying other parts with it (or sending them in the opposite direction). To correct those overblown highlights, I added one more anchor point to constrain the curve in the highlights by dragging that anchor point downward.
Step 9:
Finally, by changing that second Curves adjustment layer to Luminosity mode, that adjustment becomes applied only to the Luminosity values of the image as well. These small moves, but intricate ones, applied in Curves can bring out tremendous detail in the subject of a photograph.
Steve Weinrebe:
Mode Studio
Photography © Steve Weinrebe, Getty Images
