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My camera is the Nikon D3200 and the specs state that it has a Sensor Pixel Area of 14.85µm2 @ 24MP.

When i set my camera to JPEG (fine), I have the ability to set the picture size. Would setting it to 13.1MP allow for a greater Sensor Pixel Area or PPI in my final picture?

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  • What are you hoping to achieve by using a lower resolution?
    – James Snell
    Jan 25, 2016 at 21:08
  • Does the resulting image when you select 13.1MP include the same angle of view as when 24MP is selected? Or only the middle portion?
    – Michael C
    Jan 25, 2016 at 22:56
  • @JamesSnell lower noise/higher sensitivity in the dark at high gain?
    – Chris H
    Jan 26, 2016 at 7:27
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    @scottbb Which is exactly what happens when a Dx lens is used on a Nikon Fx body. So I was wondering if the same concept was now being offered as an option on Nikon Dx bodies to give the user such an option.
    – Michael C
    Jan 27, 2016 at 9:08
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    @MichaelClark re: Dx on a Nikon Fx body: spot on, +1. The S/M/L isn't just for DX bodies, though. On my D800E body, there are several crop choices (FX, 1.2x crop, DX crop, 5:4, 16:9 live movie view FX, and 16:9 live movie view DX). For each of those crop choices, you can choose S/M/L image size. I didn't realize how many choices there were until I looked it up. Nikon's spec sheet makes it look more confusing than it is in camera.
    – scottbb ♦
    Jan 27, 2016 at 13:36

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Greater sensor area in the way you've described it would give you a lower PPI value as it is Pixels Per Inch, of which you are recording fewer in your output file.

Theoretically, there will be some super-sampling which will provide more accuracy by averaging groups of pixels which will be treated as one later on. The effects of noise would be reduced at the expense of resolution.

In practice, doing so means a change from Raw to JPEG. This loss of information will more than outweigh any gain you might get from combining pixels. Since downscaling images in post production would also give you much better control over the process there's no justification to reduce the quality of the output from your camera.

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Would setting it to 13.1MP allow for a greater Sensor Pixel Area or PPI ...

Sensor Pixel Area and Pixels Per Inch are opposites. It's not clear if you meant this as an either/or question but it is.

Selecting a lower resolution from the same complete sensor will give you a lower PPI.

At the same time it effectively gives you a larger SPA by combining multiple photo cells to a final pixel.

You get only some of the benefits of a larger pixel, good downsampling software should be able to reduce the noise. But it won't help much in increasing your dynamic range.

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Would setting it to 13.1MP allow for a greater ... PPI in my final picture?

In terms of PPI, no. In fact, your effective PPI in the final picture is reduced. When you choose smaller image sizes in camera, when the picture is taken, the full sensor is still used. However, when the camera's processor goes to write the image to a JPEG file, the image is first downsampled. This has the effect of being able to discern fewer fine details in the reduced picture.

Nikon's D3200 specifications page gives us the following (I added the sensor conversion to inches):

  • Image sensor: 23.2 x 15.4 mm CMOS sensor (0.913 x 0.606 in)
  • Image size (pixels) [L]: 6,016 x 4,000 (24,064,000 pixels)
  • Image size (pixels) [M]: 4,512 x 3,000 (13,536,000 pixels)
  • Image size (pixels) [S]: 3,008 x 2,000 (6,016,000 pixels)

Thus, depending on whether L, M, or S is chosen in the camera settings, the D3200 will perform as either a 24 MP camera, 13.5 MP camera, or 6 MP camera. In all 3 cases, the entire CMOS sensor area is used to take the image. In other words, regardless of L/M/S setting, it is still a crop-sensor (1.5 crop factor) camera.

  • For the Large setting, no downsampling is performed. Thus the effective PPI of the sensor image is: 4,000 pixels / 0.606 inches = 6,601 PPI.
  • For the Medium setting, a 4:3 downsampling is performed. Thus the effective PPI of the sensor image is: 3,000 pixels / 0.606 inches = 4,950 PPI.
  • For the Small setting, a 2:1 downsampling is performed. Thus the effective PPI of the sensor image is: 2,000 pixels / 0.606 inches = 3,300 PPI.

Returning to your question, but addressing "Sensor Pixel Area" (I read that as effective pixel (sensel) size),

Would setting it to 13.1MP allow for a greater Sensor Pixel Area ... in my final picture?

Yes. At the following image sizes, your effective sensel size is approximately:

  • Large setting: 14.8 µm²
  • Medium setting: 26.4 µm²
  • Small setting: 59.3 µm²
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    the answer might be YES, because the effective pixel size will be increased - more sensor area will correspond to the single output pixel (because of downsampling). it does not mean that the raw pixels in the camera sensor become somehow bigger in this mode, though.
    – szulat
    Jan 25, 2016 at 16:13
  • "When you choose smaller image sizes in camera, when the picture is taken, the full sensor is still used. However, when the camera's processor goes to write the image to a JPEG file, the image is first downsampled. This has the effect of being able to discern fewer fine details in the reduced picture." Which also means the area covered by each pixel in the final image is the size of several pixels on the sensor. Fewer pixels in the same area means there is more area covered per pixel. Sensors with more detail must have more pixels per area, thus less area per pixel.
    – Michael C
    Jan 25, 2016 at 22:58
  • Or to put it simply, if you reduce PPI, then you increase the area covered by each pixel. Pixel/inch inverted is inch/pixel. 100 ppi means the same thing as 1 inch per 100 pixels which means the same thing as .01 inches per pixel. 50 ppi means the same thing as 1 inch per 50 pixels which means the same thing as .02 inches per pixel.
    – Michael C
    Jan 25, 2016 at 23:05
  • @szulat you say "the effective pixel size will be increased". True, and because the total size of all the combined sensels is still 23.2 x 15.4 mm (the sensor size), there are fewer effective pixels in the same sensor area. Therefore, the resolution is lower, or equivalently, the PPI is reduced.
    – scottbb ♦
    Jan 27, 2016 at 1:42
  • @MichaelClark, I read the original question as if "Sensor Pixel Area or PPI" were inclusive-or, as if they were correlated, as such "Sensor Pixel Area, or alternately, PPI, ...". I have reworked my answer based on reading the question as such "either Sensor Pixel Area or PPI" (exclusive-or). I apologize for my misreading.
    – scottbb ♦
    Jan 27, 2016 at 5:09

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