Why does the Sony CX405 list different still-image megapixel counts in its specifications?

Asked 12/21/2016

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The Sony CX405 specs seem to show two still-photo resolutions: an effective pixel count of about 1.71 MP for 4:3 stills, and a listed recording size of 9.2 MP at 16:9 (4032×2272). Why would the same camcorder have two different megapixel figures for still images? Is one the sensor resolution and the other the saved file size?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

9y ago

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1920×1080, the standard HD 16:9 resolution, is about 2.07 megapixels. The first set of specs lists the sensor as having 2.29 megapixels for both still and video in that aspect ratio.

The later specs give you the actual files output. The "L" resolution is 4032×2272, which is 2.1× of 1920×1080 in each direction. And, hey, half of in each direction gives 2016×1136 — which matches the 2.29 MP from the sensor spec.

One of two things is going on. Either:

  • The output image size is scaled up by 2×, which will not give any increase in image quality and in fact just wastes space, but makes the spec sound more impressive,
  • Or, the sensor is actually 4032×2272 in raw sensels, but since these have color filters and it takes a grid of four in the standard Bayer layout to get color information for a single pixel, they counting that block as an "effective pixel".

The former seems more likely, and articles like this one confirm that this is standard practice in camcorder specs. So, you'll probably get better results by using the ""S: 2.1 megapixels 16:9 (1920 x 1080)" setting — although I'd experiment to see if this is cropped or scaled down from the apparently-native 2016×1136. In fact, because camcorders are not really optimized for high-resolution stills anyway, even if the second is true, you may find you don't gain anything in terms of real detail by using the higher resolution.

Originally by user1943. Source · Licensed CC BY-SA 4.0

user1943

9y ago

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Generated from our catalog & community — verify before relying on it.

They refer to different things.

The lower number is the effective pixel count from the imaging sensor area actually used for capture. The higher number is the size of the JPEG file the camcorder outputs.

From the specs discussed, the sensor’s usable still/video resolution is only around 2 MP in 16:9, which is close to Full HD. The listed 4032×2272 output is much larger, so the camera is likely enlarging the image electronically before saving it. That does not create real new detail; it mainly produces a bigger file.

So in practical terms:

  • effective pixels = the real capture resolution from the sensor area used
  • 9.2 MP recording size = the saved image dimensions

This kind of spec difference is common on camcorders, where still-photo mode is secondary to video. The larger megapixel number is best understood as output size, not true optical/sensor detail.

UniqueBot

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9y ago

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