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Filed under: Cameras •Hardware •Production •Vendor Blog •Vendor Channels •Sony •

Pixels vs. Pixels

Pretty as a pixel: it’s called Q67.

Quick: If a 21 megapixel HDSLR records a 1080p image, how many pixels are there?  Hint: It’s a trick question.  As DPs alternate between single-sensor cameras and three-chip cameras, there’s a huge potential for confusing pixels, the microscopic rectangles of silicon on the image sensor and pixels, the digital samples that get recorded.  There may be six times as many of the first as there are of the second.  Or the numbers may be the same.  Calling both of these pixels tends to paper over these differences.  It also thwarts communication when someone means one thing but the listener hears the other.  For the sake of clarity, if not sanity, I’m learning to call the little image sensor rectangles photosites. 

A terrific explanation for preferring photosites is given by Larry Thorpe of Canon Broadcast & Communications Division, under the somewhat lengthy title of Demystifying Digital Camera Specifications, Part 1, What’s in a Pixel?  Mr. Thorpe joined with John Galt of Panavision on this series of video presentations and if you’re interested enough to be reading this article, you probably should check out these videos.

Of course, there are times when the image sensor photosites and the recorded digital pixels are completely in sync.  For example, there’s a big population of three-chip camcorders with 1920 x 1080 image sensors that record 1920 x 1080 HD.  Since I am The Sony Tech Guy, I naturally think of the SRW-9000, PDW-F800 and PMW-350 camcorders.  In these cases, everything is clear because the count of photosites equals the count of pixels, right?

Sort of.  Each pixel is actually represented by three photosites, one each for Red, Green and Blue.  So the arithmetic is 1920 x 1080 x 3 or 6.2 million photosites.  If you’re more a picture person than a numbers person, you can visualize it as follows.

We can say that this configuration has 100% RGB resolution, relative to the 1920 x 1080 HD raster.  That is to say, the Red, Green and Blue channels have full horizontal and vertical resolution—at least in the camera.  Not all of this goodness is captured by all recorders, but that’s a subject for another article.

Sony is also active in single-chip cameras, from the HXR-MC50U on up.  At the high end, we developed the Super 35mm CCD featured in the F35 digital cinema camera and more recently the SRW-9000PL Super 35mm camcorder.  The sensor uses an RGB stripe filter and double oversampling in the vertical dimension.  Now the arithmetic is 1920 x 1080 x 3 x 2 or 12.4 million photosites.  This design also retains 100% RGB resolution, relative to 1080p HD.

Both of the sensor configurations considered so far deliver a 1080p HD picture.  What about 4K? 

The answer, my friends, is on Page 2.

Disclosure, to comply with the FTC’s rules 16 CFR Part 255 This article was either written by Sony employees or for Sony by an outside contractor. It is intended for the Sony Channel on ProVideo Coalition, which Sony sponsors.

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