focus stacking

The starting point for focus stacking is a series of images captured at different focus distances; in each image different areas of the sample will be in focus. While none of these images has the sample entirely in focus they collectively contain all the data required to generate an image which has all parts of the sample in focus. In-focus regions of each image may be detected automatically, for example via edge detection or Fourier analysis, or selected manually. The in-focus patches are then blended together to generate the final image.

This processing is also called z-stacking, focal plane merging (or {{Lang|fr|zedification}} in French).{{cite web|url=http://www.lenaturaliste.net/forum/viewtopic.php?f=253&t=3397&p=50691 |title=Afficher le sujet - Proposition d'un terme français pour "focus stacking" • Le Naturaliste |website=Lenaturaliste.net |language=fr |access-date=2012-10-05}}{{cite web|url=http://www.msss.com/science/msl-mahli-instrument-description.php |title=Malin Space Science Systems - Mars Science Laboratory (MSL) Mars Hand Lens Imager (MAHLI) Instrument Description |website=Msss.com |access-date=2012-10-05}}

Getting sufficient depth of field can be particularly challenging in macro photography, because depth of field is smaller (shallower) for objects nearer the camera, so if a small object fills the frame, it is often so close that its entire depth cannot be in focus at once. Depth of field is normally increased by stopping down aperture (using a larger f-number), but beyond a certain point, stopping down causes blurring due to diffraction, which counteracts the benefit of being in focus. It also reduces the luminosity of the image. Focus stacking allows the depth of field of images taken at the sharpest aperture to be effectively increased. The images at right illustrate the increase in DOF that can be achieved by combining multiple exposures.

File:PIA18609 - First Sampling Hole in Mount Sharp .jpg's first sampling hole in Mount Sharp. The hole is {{convert|1.6|cm|in|abbr=on}} wide and {{convert|6.7|cm|in|abbr=on}} deep.]]

The Mars Science Laboratory mission has a device called Mars Hand Lens Imager (MAHLI), which can take photos that can later be focus stacked.{{cite web|url=http://msl-scicorner.jpl.nasa.gov/Instruments/MAHLI/ |archive-url=https://web.archive.org/web/20090320124731/http://msl-scicorner.jpl.nasa.gov/Instruments/MAHLI/ |url-status=dead |archive-date=2009-03-20 |title=MSL Science Corner: Mars Hand Lens Imager (MAHLI) |website=MSL-SciCorner.JPL.NASA.gov |access-date=2012-10-05}}

In microscopy, high numerical apertures are desirable to capture as much light as possible from a small sample. A high numerical aperture (equivalent to a low f-number) gives a very shallow depth of field. Higher magnification objective lenses generally have shallower depth of field; a 100× objective lens with a numerical aperture of around 1.4 has a depth of field of approximately 1 μm. When observing a sample directly, the limitations of the shallow depth of field are easy to circumvent by focusing up and down through the sample; to effectively present microscopy data of a complex 3D structure in 2D, focus stacking is a very useful technique.

Atomic resolution scanning transmission electron microscopy encounters similar difficulties, where specimen features are much larger than the depth of field. By taking a through-focal series, the depth of focus can be reconstructed to create a single image entirely in focus.{{cite journal |doi=10.1017/S1431927610094171 |title=Extended Depth of Field for High-Resolution Scanning Transmission Electron Microscopy |year=2010 |last1=Hovden |first1=Robert |last2=Xin |first2=Huolin L. |last3=Muller |first3=David A. |journal=Microscopy and Microanalysis |volume=17 |pages=75–80 |pmid=21122192 |issue=1|arxiv=1010.4500 |bibcode=2011MiMic..17...75H |s2cid=17082879 }}

File:Zassenhaus pepper mill - underside view - grinder (2019-08-06).jpg | Pepper mill, stack of 28 frames

File:Electric guide 3×2.5 mm.jpg | Stacked image of 3 × 2.5 mm electric wires

File:Philips Series 7000 shaver head.jpg | Shaver head, stack of 36 frames, retouched

File:Macrolepiota procera Parasol -20191014-RM-165319.jpg | Macrolepiota procera, stack of 15 frames

File:Orchideenblüte 2019-05-22 11-34-28 (C)-PSD.jpg | Stacked image of the inner ridge of an orchid blossom

File:Two Arecaceae in the fields viewed through a hole in a tree trunk in Laos at golden hour.jpg | Stacked image of two Arecaceae viewed through a hole in a tree trunk

File:2013-06-07 14-57-13-bille-32f.JPG | Pellet, stack of 32 frames

File:2016-01-06 14-51-04 parc-tete-or 10f.jpg | Alluaudia comosa, stack of 10 frames

File:2013-12-28 19-51-33 Litchi-20f.jpg | Mold on Litchi chinensis, stack of 20 frames

File:Skull (front) - Dolmen de Marie Gaillard MHNT ANT 2017 0 54.jpg | Skull, stack of 6 frames

File:Sympetrum flaveolum male - Kulna.jpg| Sympetrum flaveolum male, stack of 36 frames

File:Pinot_Grigio-20201027-RM-114053.jpg| Pinot Gris grape, stack of 12 frames.

File:Hindesite - Lily - Focus Stacking (by).ogv|Focus stacking images of a lily

File:Focus stacking NEC USB chip imgp0017 wp.ogv|Focus stacking images of a microchip

File:Stack and Stitch Illustration.png | Software creates from the sharpest areas in a stack of sections.

{{Div col}}

• Brenizer Method
• Deep focus
• Epsilon photography
• Focus bracketing
• Frazier lens
• High dynamic range imaging (HDR)
• Image stitching
• Image fusion
• {{section link|Microscopy|Deconvolution}}
• Shift-and-add for stacking astrophotos

{{div col end}}

{{Reflist}}

• Ray, Sidney. 2002. Applied Photographic Optics. 3rd ed. Oxford: Focal Press. {{ISBN|0-240-51540-4}}.

{{Commons category|Focus stacking}}

• [https://camerajabber.com/which-cameras-have-built-in-focus-stacking/ Which cameras have built-in focus stacking?] by Jeff Meyer, Camera Jabber Nov. 2019.

Category:Articles containing video clips

Category:Image processing

Category:Photographic techniques