Dear Ladies and Gentlemen,
does one of you know what exactly the pixel with is in electron microscopy? I found definitions on the web, but nobody gave any serious sources. So far;
pixel with describes the size of an image point (resulting from one pixel or pixel array of a CCD detector), for a certain acceleration voltage, and set up, of a TEM, in relation to this points size in the REAL object.
Sounds rather plausible, because that would fit to the half with pixel size, which is the size of half the pixels of the CCD detector depicted in the picture (mostly as a line).
Michael, what is "scientifically correct"?
For TEM (when image is digitally acquired) pixel physically exists only on CCD chip (or, for photo registration it could be described as a crystal size- or inter-crystal distance - of Ag). One can always calculate corresponding pixel size on specimen, but it is secondary characteristics.
For SEM "pixel size" is preset by operator, who can choose how many pixels per image are desirable. Of course, we could discuss optimal size of a pixel, but, as I understand, it is a different story.
Hi Michael,
A SEM is commonly modeled by means of a projective transform. After projecting one 3D space point to its corresponding 1D / 2D projected point onto the CCD detector, the real projective coordinates are truncated into integer values to take into account the discrete nature of the CCD detector. Usual modeling considerations are well described by following:
- N. Cornille, "Accurate 3D Shape and Displacement Measurement using a Scanning Electron Microscope ", 2005 - https://tel.archives-ouvertes.fr/tel-00166423/document
Regards
Thank you Stéphane, that actually is interesting becouse I wondered how this "size definition" is done in application. Still I have asked around a bit more and found out that the pixel width/size is not that consistently regarded to in electron microscopy. While one (the logical) definition is that the pixel describes the size of a area increment of the SAMPLE depicted in one pixel, as you stated other people simply regard to this with the actual size of a pixel on a CCD chip, or even worse, on a screen (but that is luckily not scientific correct).
Michael, what is "scientifically correct"?
For TEM (when image is digitally acquired) pixel physically exists only on CCD chip (or, for photo registration it could be described as a crystal size- or inter-crystal distance - of Ag). One can always calculate corresponding pixel size on specimen, but it is secondary characteristics.
For SEM "pixel size" is preset by operator, who can choose how many pixels per image are desirable. Of course, we could discuss optimal size of a pixel, but, as I understand, it is a different story.
As a follow-up of Vladimir's answer, technology-dependent projective transforms as image formation models directly applies to SEM (STEM too by extension), SPM and CLSM ( follow https://opus4.kobv.de/opus4-bam/files/137/diss21_vt.pdf and http://www.microimage.com.cn/uploadfile/xwjs/uploadfile/201102/20110228015805578.pdf ).
In what concerns TEM, the imaging model results from "an interference of several (spherical) waves admitted by the opening of the contrast aperture" ( excerpt from http://www.xray.cz/ms/bul2001-1/karlik.pdf ). "If the imaging is incoherent, [...] the intensity transfer is linear and thus the Z-contrast imaging gives direclty interpretable images..."
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