Photoshop has a feature that can precisely adjust and remap the different tonal values of an image or any photography color correctionchannel of an image. This is found in the curves feature of Photoshop which can be appropriately accessed by going to the Image tab > Adjustments > Curves.

This command in Photoshop is very unlike the "Levels" command of Photoshop which has limited points which concern an image’s highlights, shadows and midtones. With the Levels command of Photoshop, you only have command of dark, bright and gray values of an image. With regard to the Curves command in Photoshop, you have up to 14 point to control. However, given this wide range of control points, it is absolutely rare for you to use more than a few in order to satisfactorily color-correct an image in Photoshop.

When you go to access the Curves dialog box, you will notice a horizontal and vertical axis. The horizontal axis in the dialog box of the Curve dialog box are the ones which stand for the current estimations of the various pixels in the image. The vertical axis in Photoshop is used to represent the various tonal values of the pixels after the curve is utilized. The automatic setting of the curve in the Curves dialog box is a straight 45-degree angle line.

The way that the default curves setting is set up is that each input value is exactly the same for the output value. You may also add various points across the default curve by clicking across the graph. However, as you introduce more points to the curve, you may drag them to reshape the curve and you can then essentially adjust the tonal values of that specific point especially those areas which are closest to the point.

For example, in the Curves dialog box, you will always start with a straight 45-degree line. If you are dealing with an RGB image, that will start from the shadows at the bottom left corner ascending up to the highlights and the upper right corner. If you drag an RGB curve upward, you will essentially add light to the image. However, since you primarily select RGB as the channel the you start out with, you will affect the brightness of all of the color channels. However, this is not the most optimal way to go about color-correcting an image. It would be better if you adjust the curve of each channel until it is suitable enough for you.

There are a lot of effects that you are able to achieve using the Curves dialog box. Although it would be good to adjust curves with caution as not to drastically alter the overall color cast of the image. This is a very delicate tool for Photoshop and if you become familiar enough with the settings and how it works, you may find yourself using the Curves tool more often.