Many Photoshop users learn to use the Levels dialog and then never progress to learning how to use the Curves. In this Photoshop article I will give you several reasons why learning to use the Curves will make you more of an expert with Adobe Photoshop.
In digital photography editing, both the Levels and the Curves are used for one of the single most important editing tasks: image tone control. Whenever you have a photograph that has less than perfect contrast, i.e. the contrast is either too low or too high, you need to use some form of tone control.
Both the Levels and the Curves allow you to alter the black and white end points of the tonal range in the image. Adjusting the end points allows you to change the global or overall contrast of a photograph; the method and affect is the same whichever of the two commands you choose to use.
Both commands also allow you to change the appearance of the intermediate, or grey, tones in-between the black and white end points. However, the important difference between the two commands is that a Levels adjustment proportionally changes all of the tones in the tonal range; whereas the Curves allow you to choose which portion of the tone scale you wish to adjust. Levels is a linear adjustment but Curves are a geometric adjustment (in fact, this difference is in the names levels and linear, curves and geometric). This is a massive difference and using Curves rather than Levels will elevate your editing skill to a professional level.
The big question is which should you use?
This is quite straightforward if you consider the following points.
Use Levels when:
• You only want to adjust the black or white end points to adjust global contrast• You want to lighten or darken the entire tonal range. This is normal to adjust exposure errors.
• You want to maintain the visual relationship of the values of the intermediate tones.
Use Curves when:
• You want to subtly adjust the visual relationship of the tone values. For example lighten the lights and darken the shadows. This usually requires an ‘S’ shaped curve adjustment.• You want to adjust only the light tones or only the dark tones.
• You want to adjust the tones in only a small section of the overall tonal range.
• You want complete control of your tonal editing.
If you play with the Curves dialog for 10-15 minutes you will feel much more comfortable with the process. And don’t forget that if you use the Curves as an adjustment layer you can always change the affect without damaging your original photograph.
(Related Article : How to use Color Curves in Photoshop)