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This site already has a question around what is pixel density, but it doesn't mention pixel pitch at all. I am wondering what the relationship is, and what is important about the relationship to photographers today.

Not to foil the answers from others, but this fun equation is what spurred the question:

pixel pitch = 1/sqrt((pixel density per cm^2)/(10000^2))

I have no idea really what the above equation means, or even if it is accurate. I found it at this thread at dpreview.com.

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I sometimes see pixel pitch referred to as the "size of one pixel". Sorry I do not know if this fits any scientific definition. But if it does, pixel pitch is simply a measurement of size. –  Gapton Dec 28 '11 at 7:05
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Pixel pitch is the size of one pixel + the size of the gap between adjacent pixels. –  Edgar Bonet Dec 28 '11 at 10:27
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Here is a simple formula for pitch in microns: pixel_pitch = (sensor_width / pixels_per_row) * 1000. So, in the case of the 1D X, which has 5184 pixels per row in a 35mm format, pitch = (36mm / 5184) * 1000 = 0.0069444mm * 1000um/mm = 6.95um. Pixel density could be measured per millimeter, per centimeter, per inch...doesn't really matter...it is basically the pitch per distance (or better, per area, so pitch squared). So, no, pixel pitch and pixel density are not exactly the same, although they are related. –  jrista Feb 27 '13 at 19:41

1 Answer 1

up vote 9 down vote accepted

It's just a reciprocal relationship. Where pixel density measures, say, the number of pixels per inch, pixel pitch measures the number of inches per pixel (or the center-to-center spacing between pixels).

Pixel pitch expressed as a linear measurement, and if the pixels are non-square you may see two values specified. Pixel density, on the other hand, may be expressed as a linear measurement (pixels per inch or millimeter or what have you) or as an area measurement (pixels per square inch or pixels per square millimeter) -- your equation assumes an area measure of pixel density and square pixels, and converts to a linear value.

I should probably add that pixel pitch is usually used to state device specifications (screens or sensors) -- you wouldn't often see it used to describe, say, the resolution settings you used to print an image.

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6  
I would just add that the relationship between pixel pitch and the areal pixel density is simply density=1/pitch². No extra factor needed if units are used consistently. The factor 10000 in the quoted formula is for converting cm to µm. –  Edgar Bonet Dec 28 '11 at 10:25
    
@EdgarBonet Good point. A lot of what looks like complications in any mathematical equation is often just unit conversion, and with "magic numbers" it can be harder for the uninitiated to understand what's going on. –  user2719 Dec 28 '11 at 15:07

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