56 mp fx ?

Started Feb 23, 2013 | Discussions thread
fft81 Contributing Member • Posts: 951
Re: Fact or fiction?

Every one above this post is wrong! Here are the facts:

The pixel count is only half of the story. Quality of each pixel is the other half. Can a 100MPx sensor be made? Yes it can. Will that 100MPx sensor produce image file better than today's D4's 16MPx sensor? No it won't. Nokia 808 has 41MPx sensor. The manufacturer states that the phone is capable of producing photos on par with 6 to 7 MPx DSLR. It all has to do with diffraction and amount of light falling on each pixel. Yes you can zoom in and pixel peep on the 41MPx image, but when you look at it in full view it will look as good as 6MPx dslr shot. It is not hard to cram 100MPx onto a FF sensor; it is near impossible to cram 100MPx onto FF sensor while maintaining the quality of each pixel on par with even the d90 pixels.

It's also a balance triangle. Decrease pixel pitch, you need to also increase shutter speed to overcome camera shake. This means the amount of light falling on each pixel is decreased by X^2 where X is your pixel pitch change. What it all boils down to is that to increase resolution by a factor of 2 you need to increase the light sensitivity of each pixel by a factor of 2. To do that you need to either design a brand new pixel or increase excitation voltage to each pixel by a factor of 2. If you increase excitation voltage to each pixel by a factor of 2 you will increase its power consumption by 2^2=4 times, so it draws 4 times more power, heats up 4 times more and drains your battery 4 times faster. For the D800 vs D700 the resolution bump was 3x so if D800 used the same pixel technology as d700, it would consume 9x more power. So, the d800 pixels are actually rather different than d700 pixels (more pure materials, better precision, better pixel-to-pixel isolation etc). Even if you can design a perfect pixel a pixel on its own can not differentiate between signal and noise, so even in a perfect pixel you will eventually develop very low signal-to-noise ratio, so to really get a clear picture you would need to average the information out across multiple pixels, hence what is the point of making smaller pixels in the 1st place. Noise is generated by sensor itself, plus there is noise in the actual light hitting the sensor. Noise in the light is your hard limit for resolution. Noise generated by the sensor is increased by higher ISO, which is ultimately is the problem with Nokias 808 camera and the reason for its image being equivalent to a 6MPx image from a real modern DSLR. Bumping up ISO is what adds the sensor generated noise and it multiplies both signal and noise from light itself. Bottom line is that increasing ISO always decreases signal-to-noise ratio. For a smaller pixel pitch you have to increase iso and so add noise. Doing so reduces your total resolution to a lower number than was gained by using smaller pixel pitch.

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