Sensor/Pixel Quotient-----Sqm, MP and SPQ

Started Jul 3, 2014 | Discussions thread
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Stephen McDonald
Stephen McDonald Forum Pro • Posts: 13,379
Sensor/Pixel Quotient-----Sqm, MP and SPQ

We are often informed about the sensor size-type of cameras in inches or fractions of them. This is very different from their actual sensing areas and is misleading. We also are told of the total number of pixels they have, in Megapixels (MP). So I think there should be a simple and concise way of quantifying the sensor size in relation to the number of pixels. The term "pixel-density" may be used for this, but this is only rarely mentioned and may not be quantified.

So I suggest that the size-type in inches be discarded and replaced by the number of square millimeters (Sqm) in a sensor's active area. The Sqm of a sensor would be the only way its size-type was described and it would convey its true functional size.

Then what is perhaps an even more important figure, pixel-density, could be calculated. So by dividing the square millimeters of the active area by the MP on the sensor, the Sensor/Pixel Quotient (SPQ) could be calculated. This single value could tell a lot about the relationship between sensor size and the number and size of pixels. The higher the SPQ number, the larger the pixels and the lower the sensor's pixel-density.

There are many more things about a sensor and its pixels that determine the image quality it provides, but the SPQ could be a good and standard starting point of reference. If there is any argument against larger sensors and larger pixels being an advantage, then what purpose would full-frame sensors have?

Using the SPQ number of a camera, shows decisively how much more space is provided for each pixel, on larger sensors. I've calculated the SPQ number for several cameras with which we're familiar.

Models such as the HX400V, with a "1/2.3-inch" sensor and 21.1 total MP, have an SPQ number of only 1.4. The RX-Series cameras with "1-inch" sensors and the same number of pixels, have an SPQ of 5.5. APS-C cameras with 21.1-MP, have an SPQ of 17.5. And full-frame sensors of the size Sony uses and with 21.1-MP, have an SPQ of 40.9. The Sony RX1, using an FF sensor, with 24-MP, has an SPQ number of 35.8.

Comparing two types of cameras, such as the HX400V (SPQ 1.4) and the RX1 (SPQ 35.8), that we discuss here often, by using their SPQ numbers, gives a striking way to conceptualize how much difference there is in the pixel-density on their sensors. Even if no one else goes along with this, when I make a reference to "Sqm" and "SPQ", you'll know what I mean.

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Sony Cyber-shot DSC-HX400V Sony RX1
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