Understanding+Curves

To find the curves Tool you may need to select Show all menu items from the menu.

An Amazing Tutorial from David J. Nightingale worth visiting!

http://www.chromasia.com/tutorials/online/curves/curves_2.php

**Introducing the Curves dialog** The Curves tool, like the Levels tool, allows us to make simple adjustments to the tonal range of an image, but unlike the Levels tool – where you only have control over the black point, white point, and mid-tones – the Curves tool provides a much higher level of control, not least because it allows you to manipulate both the white and black points//and// 15 additional anchor points that may be positioned anywhere within the original image’s tonal range.

To use the Curves tool you need to either select it from the Image menu (Image → Adjustments → Curves)


 * Setting white and black points**

What you will notice is that this adjusted Curve is steeper than the original. This stretches or expands the tones within an image, thereby increasing the contrast. Alternatively, if you decrease the slope, you compress the tonal range and decrease the contrast. If you hover your mouse over the ‘show curve’ and ‘show histogram’ labels below the following three images you will be able to see the Curve that was applied to each image and the resultant histogram: no change with the first image, a decrease in tonal range/contrast with the second (by decreasing the slope of the Curve), and an increase in tonal range/contrast with the final image (by increasing the slope of the Curve).

We can also use the Curves tool to alter the mid-tones of an image. With the Levels tool this was a simple matter of dragging the mid-tones slider (to the left to lighten an image, and to the right to darken it), but with the Curves tool it’s marginally more complicated insofar as we need to add an anchor point to control this area of the tonal range. To add an anchor point at any position on a Curve you simply need to click the position on the Curve where you want to insert it. To control the mid-tones, this needs to be mid-way between the black point and white point, in this case almost exactly in the middle of the grid. At this stage this has no effect, as it hasn’t altered the shape of the Curve in any way, but if I drag this point towards the top-left corner of the dialog it will increase the brightness of the mid-tones. Conversely, if I drag it down towards the bottom-right corner, it will decrease their brightness. The further you drag the anchor point, the greater the effect. || If you decide that you’re not happy with the Curve you have constructed you can delete the control points, by selecting them and then deleting them with the delete key, or you can hit the Cancel button (which closes the dialog without making any changes).
 * Altering the mid-tones**
 * [[image:http://www.chromasia.com/tutorials/online/curves/images/curve_60-200mid-point.jpg]]
 * Resetting the Curves dialog**

If you hold down the Alt (Or Option for Macs) key you will notice that the Cancel button turns into a Reset button. If you click this button all your control points will be removed and you can start again: re-entering your control points, and adjusting your Curve. In this section we have discussed some of the basic ways in which the Curves tool can be used, including setting white and black points and altering the mid-tone areas of an image. In the next section we will move on to consider S-Curves and how to construct them to effectively enhance your images.