Why is sharpening usually the last step in post-processing?
Asked 3/4/2011
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2 answers
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People often recommend doing sharpening at the end of editing, and sometimes imply it should always be the final step. Why is that? If an image already looks acceptably sharp to me at 100%, what does sharpening add, and why not do it earlier in the workflow?
Originally by user2559. Source · Licensed CC BY-SA 4.0
user2559
15y ago
2 Answers
31
First of all, sharpening isn't (at least primarily) to compensate for pictures that weren't sharp -- it's primarily to reverse (or least ameliorate) the effects of interpolation that's inherent in converting the data from a typical Bayer-pattern sensor into a recognizable image.
There's also (at least typically) interpolation done when you resize an image. To compensate for that interpolation, you need to do the sharpening after the interpolation -- but you want to keep the image full size for as much post-processing a possible to maintain maximum quality in your editing. Therefore, you want to do all the other editing, then size the picture for the target, then do a final sharpening step to compensate for the interpolation in the sizing.
You might also want to read Patrick Lavioe's paper on sharpening in three steps.
Originally by user603. Source · Licensed CC BY-SA 4.0
user603
15y ago
0
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Sharpening is usually a finishing step, not just a fix for bad focus. Even a well-focused digital image can benefit from sharpening because some softness is introduced by demosaicing and by later interpolation when you resize the image.
The main reason to sharpen last is that many edits can change or reduce apparent sharpness: resizing, rotation, cloning, compositing, and similar operations. If you sharpen before those steps, the effect may be weakened or altered, and you may need to do it again.
Output size also matters. Sharpening that looks right at full resolution may have little visible effect after downsizing for the web, and print often needs different sharpening than screen viewing because viewing distance and medium change the perceived sharpness.
A common workflow is:
- Do your main edits on the full-size image.
- Resize/crop for the final use.
- Apply final output sharpening for that specific destination.
So if your image already looks good, you may not need much sharpening—but when used, it’s most effective as the final, output-specific step.
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