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How to Use Tonal Curves for Image Correction
A tonal curve can make an impressive improvement to an image.
There are two ways to use a curve:
- Applying a curve directly; this alters the image pixels (not recommended in most cases, but OK for a quick adjustment).
- Adding an Adjustment layer; this adjustment layer can be tweaked at will and does not alter the underlying image pixels (recommended).
In general, always work with 16-bit images and a wide-gamut color spaces. Convert 8-bit images to 16-bit if need be (e.g. JPEGs). Save the “master” image as a layered Photoshop document in order to preserve the layers; output JPEG or TIF or whatever using that master image.
Experience and experimentation are key to learning to use the Curves facility. Set the Curves dialog for . With this setting, the left side of the histogram is black and the right side is white.
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Diglloyd Making Sharp Images articulates years of best practices and how-to, painstakingly learned over a decade of camera and lens evaluation.
Save yourself those years of trial and error by jump-starting your photographic technical execution when making the image. The best lens or camera is handicapped if the photographer fails to master perfect shot discipline. High-resolution digital cameras are unforgiving of errors, at least if one wants the best possible results.
- Eases into photographic challenges with an introductory section.
- Covers aspects of digital sensor technology that relate to getting the best image quality.
- Technique section discusses every aspect of making a sharp image handheld or on a tripod.
- Depth of field and how to bypass depth of field limitations via focus stacking.
- Optical aberrations: what they are, what they look like, and what to do about them.
- MTF, field curvature, focus shift: insight into the limitations of lab tests and why imaging performance is far more complex than it appears.
- Optical aberrations: what they are, what they look like, and what to do about them.
- How to test a lens for a “bad sample”.
Intrigued? See Focusing Zeiss DSLR Lenses For Peak Performance, PART ONE: The Challenges, or (one topic of many) field curvature.
