Wednesday, October 24, 2007

Adobe Camera Raw's Tone Curve

Adjusting Curves can be intimidating, even for the most experienced analyst. The dialog and controls are not necessarily intuitive. For the novice, most don't even venture close to a curves adjustment. Today, we'll go over the basics and show you how the Tone Curve works in Adobe Camera Raw 4.2.

Remember, you can now work with JPEGs and Tiffs in Camera Raw. If you are shooting stills in the field, you should be shooting in Raw. If you have an older camera that doesn't support Raw, you should be able to shoot in JPEG. Either way, you'll be able to follow along with today's post.

Contrast is the measure of the grey values between an image's shadows and highlights. Not enough contrast and the image seems flat. Too much contrast and the image becomes a modern art masterpiece. Brightness is the overall measure of lighting in an image. Too dark, shadow detail is lost. Too light, highlight detail is lost. Just right usually equals a balanced image with detail retained in shadows, midtones, and highlights. How do we get there? The Contrast Slider in the Basic Panel can help, but is not the best tool in solving this problem. There is simply not enough control built into that slider to be of much use to us. Skip it and click on the Tone Curve panel's icon, the tab just to the right of the Basic panel's icon.

If you are upgrading from a previous version of Camera Raw, you'll notice that the familiar Point Curve has been shoved aside by the new Parametric Curve tab. What's the difference? We'll see.

The Point Curve is a good place to start as it performs much like the Curves dialog in Photoshop, but not exactly the same. One of the first things that you'll see is a drop-down menu called Curve. The default setting for this menu is Medium Contrast. Click on it and you'll see all of your choices; Linear, Medium Contrast, Strong Contrast, and Custom. Choosing Linear returns the image to its initial curve state, Medium Contrast kicks it up a notch, and Strong Contrast really gives it some punch. Remember, the steeper the curve, the more contrast it creates.

The easiest place to start is to choose one of the preset curves. For the moment, we'll stick with the Medium Contrast settings. You'll see that the line that runs from bottom left to top right has some points already mapped. Click on one of them and drag it up and down a bit. Notice that when you drag it up, the image lightens and when you drag it down, the image darkens. If you don't have the steadiest of hands, you can click on a point and use the arrow keys to move the control point around. If you are new to curves, you'll notice that the left side of the curve adjusts the shadows and the right side of the curve adjusts the highlights.

Having made some simple changes to the preset curve, you can see the difference in your image. More or less contrast is added as you slide the points up and down. If you want to start from scratch, you can choose Linear from the menu and add the points yourself. A simple click on the line adds a control point. You can then adjust them as described above. If you don't want that point anymore, just click and hold it - then drag it off the screen to throw it away.

If you are working on a lot of images from the same source and want to save these settings and use them again, click over on the Presets Icon (the furthest to the right). You may see a large white area, that's OK. Click on the fly out menu just to the top of the white space and select Save Settings. you can check or un-check settings as you like or use the drop-down menu. Since we just worked in the Point Curve panel, we can choose that from the drop-down menu and click save. When you go back to work in the Point Curve panel, click on the preset drop-down menu and you will see your saved settings at the bottom.

Congratulations, you've just adjusted the contrast in your image using Curves in ACR! But wait, there's more!

Remember when you first clicked on the Tone Curve icon, it was the Parametric Curve panel that was displayed. From there, we clicked on the Point Curve tab. Let's go back and look at the Parametric Curve panel.

You'll notice that there are four sliders on the bottom of the panel that control the Highlights, Lights, Darks, and Shadows, or the four different areas of the curve. Before you start, click back to the Point Curve panel and make sure that Linear is selected. When you first open the dialog, Medium Contrast is selected by default. Therefore, if you start with the Parametric Curve, all the changes you make will be on top of the Medium Contrast curve. Selecting Linear returns the image to its starting point.

The easy way to work the sliders is to remember that right=brighter and left=darker and the controls work the curve from top to bottom, or from highlights to shadows. To drive up the  contrast, we need to create space between the highlights and shadows. We can do this by sliding the highlights and lights sliders to the right and the darks and shadows sliders to the left. The more we slide the sliders, the steeper the curve becomes and the more kick we give to the contrast.

You can have even more control over the effect using the Region Divider controls. These are the the triangle shaped controls directly under the vertical lines that dissect the curve. Click the control on the far right to effect the lights/highlights. Slide the control to the right and you give more control of the area to the lights slider and less to the highlights slider, and so forth. Feel free to experiment. Dragging the outside controls to the center steepens the curve even further, adding a ton of punch to your image.

Now that you've worked with both curve panels, give it a try. Once you start working with ACR as the entry point for your work flow, I think you'll be hooked.

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