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How to Downsample and Sharpen an Image
Downsampling an image means to reduce its resolution (upsampling increases it).
Downsampling can be done with any type of image: TIF, JPEG, PNG, GIF, etc. Bit-depth (8-bit or 16-bit) doesn’t matter for downsampling, unlike Curves and RAW conversion.
There are a number of reasons to downsample an image:
- To reduce download time.
- To fit on a reasonable size screen.
- To meet publishing requirements (e.g., 180/240/360 dpi for an 8 X 10 page in a magazine).
- Proofs at less than full resolution, copyright submittals, etc.
- In acknowledgment that full image resolution contains less (possibly much less) actual resolved detail than the dimensions imply.
- For purposes of comparison.
- To reduce digital artifacts such as staircasing and jagged edges, e.g. “oversampling” followed by a size reduction.
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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.
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