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The Curves adjustment in Adobe Photoshop has a reputation for being challenging for some photographers. In this workshop, Photoshop expert Tim Grey takes you step by step through every aspect of the Curves adjustment, helping you truly understand the concepts behind it so that you can quickly and easily maximize tonal range, optimize contrast, and enhance your photos' color balance. Note: This course was recorded in Photoshop CS5, but was created with users of both Photoshop CS5 and Photoshop CS4 in mind.
The curves adjustment is all about flexibility and control, and that flexibility and control even extend to the display of the curves controls on the adjustments panel. In this lesson we'll take a look at the curves display options. I've already gone ahead and added a curves adjustment, and I've even applied some relatively arbitrary adjustments to this curve adjustment, in order to be able to better see some of the curve's display options as we're looking at them. So in this case, with a curves adjustment layer already added, all I need to do is click on the panel popup menu found at the top right corner of the Adjustments panel, and then choose Curves Display Options from the popup menu. This will bring up the Curves Display Options dialog, where we can adjust the various settings related to how curves is displayed on the Adjustments panel. The first option is whether or not we want to show the amount of light or pigment on the curve.
What that really means is if we raise the curve, are we increasing the amount of light, and therefore lightening the image, or are we increasing the amount of pigment and therefore darkening the image? For photographers it usually makes the most sense to show the amount of light. And that's the option I have set here. So you can see my main curve, the RGB curve shown in black here, has been pulled downward. That means less light, and therefore the image will be getting darker.
I can switch this option so that I'm seeing how much pigment is being added or subtracted to the image. That won't affect the behavior of the curve but will merely change the way the curve is presented. So in this case, my curve is going downward because I've darkened the image, I've subtracted light. If I switch this curve, you'll see that I've darkened the image by increasing the amount of ink or pigment. It's really just a matter of how you think about the curve. But once again, for photographers I think it makes the most sense to keep this option set to light. Next we have a series of check boxes that allow us to control which particular items are shown as part of our curves adjustment.
The channel overlays relate to the individual color channels for curves. In this case, I've switched away from my RGB curve and applied changes to the red, green and blue curves individually. Those curves will affect the overall color in the image. And by turning on the channel overlays check box, I'm able to see those individual color curves. Keep in mind that I'm not able to adjust those curves while I'm in the RGB curve.
Turning this option on merely shows me what those curves are doing, so that I can better evaluate the effect within the image. The histogram checkbox allows you to enable or disable the display of the histogram display that is shown behind the curve. This provides us with an indication of the distribution of overall tonal values within the image. And it can be helpful to review that histogram while you're working on curves. For example, in this case I can see that there are lots and lots of pixels that are just a little bit darker than middle gray.
That information can sometimes be helpful as I'm deciding where I want to focus my adjustment in curves. Another helpful option is the baseline option. When you have the baseline option turned on you'll see faint, gray line that shows you the original starting point of the curve. This makes it much easier to read the curve because you can immediatelly evaluate whether any portion of the curve is currently above or bellow the original starting point. In other words, we can quickly see whether we've lightened or darkened particular ranges of tonal values within the image. The intersection line option determines whether or not we'll see an intersecting line as we're moving an anchor point.
I'll go ahead and click Okay for the moment, to close the curve's display options dialog, so that you can see that in action. If I click and drag on an anchor point, notice that I have a horizontal and vertical line attached to that anchor point that extends the full height and width of the curve's display area. This can be helpful when you're trying to evaluate the before and after values using the gradience at the bottom and left of the curve's display area. By having lines drawn from the anchor point to those gradients, it's much easier to see the relative values as you're applying your adjustment. I'll go ahead and bring the curves display options dialog back up, and as you can see we can turn off any of these options if we decide that they present too much clutter.
I personally like having all of them turned on, but if you find that it's a little bit cluttered you can certainly turn off any or all of these options. Finally we have an option to change the display of the grid that appears behind our curves display. The default is to show lines at 25% increments but we can change that to 10% increments if we prefer. Again this does not change anything about the behavior of curves but rather just provides a reference for you while you're working.
While it doesn't actually give me any higher degree of control, I do prefer the 10% option just so that I can see a little bit finer break down of the various tonal ranges while I am working with curves. When you've adjusted the settings to your liking in the curves display option dialog, simply click Okay. Those settings will continue to take effect for all curves adjustments you add to any image until you make any changes in the curves display options dialog. And as long as we're talking about the display options, it's worth noting that by default, the histogram that is displayed is based upon cached data. That means it's not completely, 100% accurate.
If you'd like to update that histogram, to make sure that it is completely accurate, based on the original pixels. And note, this histogram does not reflect changes you've applied with curves. But rather reflects the appearance of the original image that you're applying this adjustment to. If you'd like to update that histogram, simply click the refresh histogram button at the bottom left corner of the curves display. If you watch carefully while I click this button, you'll see a subtle change in the histogram itself. Not a major issue, but this can be helpful and more importantly it answers the question of what this little button means when it does appear. Keep in mind that the curves display options really relate to personal preference.
They don't change the behavior of the curves adjustment, but rather allow you to control how certain information is presented to you when you're working with a curves adjustment layer.
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