Curve Direction

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Today’s Question: When a Curves adjustment is used to increase or decrease brightness in an image, some photographers drag the curve center point at a roughly 45 degree angle toward the top left to increase brightness or toward the bottom right to decrease brightness. Other photographers drag the center point vertically toward the top to increase brightness or vertically toward the bottom to decrease brightness. And the arrow keys also facilitate fine adjustment using this approach. The resulting tone curves are plainly different with each approach. Which is the best approach for overall image brightness adjustment?

Tim’s Quick Answer: There isn’t a single “correct” direction to drag an anchor point with the Curves adjustment. Rather, what is important is the specific relationship you’re defining between the “before” and “after” value for tonality. The optimal result will vary based on the specific image you’re working on.

More Detail: If you drag an anchor point directly upward (or downward) at the precise center of the curve, you will be applying an equal adjustment to the highlights and shadows in the image. If the anchor point is dragged out at a 45-degree angle toward the top-left, you will have a stronger effect on the highlights than on the shadows.

What ultimately matters here is the shape of the curve and the effect you want to have on the image. Keep in mind that what you’re altering with the curve is the relationship between the “before” and “after” values within the image. How you adjust the shape of the curve depends on how you want to adjust the tonal values in bright versus dark areas of the image.

It is also worth keeping in mind that in many (if not most) cases you will want to add more than one anchor point for the Curves adjustment. This enables you to have a different effect in highlight areas versus shadow areas of the image, for example. In some cases you might want to lighten the shadows and darken the highlights, while in other cases you might want to darken the shadows and lighten the highlights. And of course with some images you might want to only lighten or darken, though with an emphasis on specific tonal ranges.

So again, it is important to consider the shape of the curve for a Curves adjustment based on how you want to alter the appearance of the specific photo you’re working on.