Pixel density, please explian.

[jvanmil]

Hey All

As i am currently looking into different camera options i come across different sensors with different pixel densities. Can you please explain what is meant and how does it work?

I currently have a Canon 400D with 10.1 effecive MP and a pixeldensity of 3.1mp/cm2. i am looking at the panasonic GF1 for example with 12.1 effective mp and a density of 5 mp/cm2. Can you please esplain me the difference?

Thanks Jan
--
'In Wildness is the Preservation of the World'

 

[Dansk]

It's pretty straightforward. Pixel density is simply how many pixels--light sensitive points--there are on the sensor in a given area. Since the GF1 has more pixels on a smaller sensor than the 400D, its pixel density is higher. Total pixels divided by total sensor area (in cm) gives you pixels per cm2.

Simple as that.
--

• Kevin

 

[Mark S Abeln]

Pixel density is roughly correlated to the size of the pixels, or rather, it gives an upper limit to the pixel size.

You want big pixels to gather lots of light and therefore reduce noise. Generally speaking, low pixel density is a good thing up to a point.

The numbers don't tell you about the details. You can have a low pixel density, but still have small pixels, widely spaced. Some manufacturers counteract this by putting lenses over the pixels, gathering more light. There are other factors also, which is why premium sensors get premium prices.

--
http://therefractedlight.blogspot.com

 

[Guv]

The single most important factor for better image quality at the sensor level is simply the size of the sensor (more importantly than that is the lens you use, but we'll talk about that later). People get caught up in pixel size and density, microlenses and such, claiming more or less noise because of those factors, but in the end the most important thing when comparing pixels is the overall size of the sensor, not the pixels. This becomes intuitive once you take a moment to consider how the original sensor sized image must be enlarged to your viewing size. The sensor on your 400D is 22.2 x 14.8 mm. The GF1 sensor size is smaller, at 18.0 by 13.5 mm. This might not sound like a huge difference, but the 400D's sensor is 35% larger in area. Gapless microlenses or not, the 400D is gathering a larger amount of light, i.e. more information for color and density depth, than the GF1. And it simply requires less enlarging to get to the image level, be it a 4x6" print or 1200x1800 websize or whatever you're viewing it at. The GF1 might have fancier electronics and noise reduction that make it appear equal at first glance, but on the RAW image level it simply won't stack up. Now, whether the casual observer notices this in the final product might be entirely negligible. The smaller form factor of the GF1, which I'm guessing is part of the appeal for you, might be more important to you than slight image quality improvement and better control over DOF (another aspect of larger sensors).

Also a factor is that array of lenses available to you with the Canon mount that simply doesn't exist with the M4/3 mount. Put briefly, the 400D with an L prime is going to beat the socks off the GF1 with any lens on it, for both quantitative and qualitative reasons.

If you're a snapshot taker and just want something that fits in your bag better, maybe the GF1 is a better option for you. But purely for image quality, stick with the 400D and get a better lens.

--
http://andymcelroy.smugmug.com

 

[Great Bustard]

Hey All

As i am currently looking into different camera options i come across different sensors with different pixel densities. Can you please explain what is meant and how does it work?

I currently have a Canon 400D with 10.1 effecive MP and a pixeldensity of 3.1mp/cm2. i am looking at the panasonic GF1 for example with 12.1 effective mp and a density of 5 mp/cm2. Can you please esplain me the difference?

The pixel density is just the number of pixels divided by the area of the sensor:

400D: 2.22 cm x 1.48 cm = 3.29 cm², 10.1 MP / 3.29 cm² = 3.1 MP / cm²
GF1: 17.3 cm x 13 cm = 2.25 cm², 12.1 MP / 2.25 cm² = 5.4 MP / cm²

Although DPR, for some odd reason, uses 1.8 cm x 1.35 cm for the dimensions of the GF1 sensor, which is why their computed pixel density is 5 MP / cm² instead of 5.4 MP cm².

Anyway, moving right along, pixel density is an irrelevant measure in terms of IQ (image quality). The relevant measures are sensor size and pixel count. These two topics are discussed in detail here:

http://www.josephjamesphotography.com/equivalence/#lensvssensor

and here:

http://www.josephjamesphotography.com/equivalence/#megapixels

 

[jvanmil]

Thanks All!

Jan
--
'In Wildness is the Preservation of the World'

 

[Fish323]

Anyway, moving right along, pixel density is an irrelevant measure in terms of IQ (image quality). The relevant measures are sensor size and pixel count.

I concur with what you are saying but the best way to compare is by obtaining a pixel density for each sensor. Without that comparision all you have is data for different sensor sizes without any method of comparison.

 

[William Carson]

I still find the use of 'pixel density' rather than simple pixel size unnecessarily complex. Pixel density does not indicate how large the pixel is which is where you start when you want to see how much dynamic range the sensor is capable of. Other factors add in from that point but a knowledge of size can be a useful measure.
Will

 

[Josefin]

GF1: 17.3 cm x 13 cm

That's a bloody big sensor, Big Bird. Did you know that some people claim that Four-Thirds sensors are small?

--
Rikke

 

[Mark S Abeln]

GF1: 17.3 cm x 13 cm

That's a bloody big sensor, Big Bird. Did you know that some people claim that Four-Thirds sensors are small?

I'd like a sensor that big, but for the price they charge for those things, they better have a front doorbell.

--
http://therefractedlight.blogspot.com

 

[Great Bustard]

Thanks All!

Glad to be of help!

I concur with what you are saying but the best way to compare is by obtaining a pixel density for each sensor. Without that comparision all you have is data for different sensor sizes without any method of comparison.

Once again, pixel density is an irrelevant measure in terms of IQ . The relevent measures are the sensor size and the number of pixels. You need these two different numbers to make a meaningful statement about IQ -- dividing them to get a single number tells us nothing.

I still find the use of 'pixel density' rather than simple pixel size unnecessarily complex. Pixel density does not indicate how large the pixel is which is where you start when you want to see how much dynamic range the sensor is capable of. Other factors add in from that point but a knowledge of size can be a useful measure.

Pixel size is also irrelevant. It is the size of the sensor , not the pixel, that matters, as well as the number of pixels. Of course, the lens also plays a central role, as does the efficiency of the sensor. But neither the pixel density, nor the pixel size, are a meaningful measure in terms of IQ.

GF1: 17.3 cm x 13 cm

That's a bloody big sensor, Big Bird. Did you know that some people claim that Four-Thirds sensors are small?

Heh! Well, I was thinking about the new camera Olympus was releasing. : )

But, yes, of course, I meant 1.73 cm x 1.3 cm!

I'd like a sensor that big, but for the price they charge for those things, they better have a front doorbell.

Yeah, but can you imagine the size of the lenses for that sensor?! And, well, yeah -- there is the doorbell to consider as well.

 

[Fish323]

I still find the use of 'pixel density' rather than simple pixel size unnecessarily complex. Pixel density does not indicate how large the pixel is which is...

If you have a pixel density of 42million per cm2 then surely the area each pixel occupies is 1/42,000,000 of a cm2? Or have I completely misunderstood this?

 

[Fish323]

Thanks All!

Glad to be of help!

I concur with what you are saying but the best way to compare is by obtaining a pixel density for each sensor. Without that comparision all you have is data for different sensor sizes without any method of comparison.

Once again, pixel density is an irrelevant measure in terms of IQ . The relevent measures are the sensor size and the number of pixels. You need these two different numbers to make a meaningful statement about IQ -- dividing them to get a single number tells us nothing.

I still find the use of 'pixel density' rather than simple pixel size unnecessarily complex. Pixel density does not indicate how large the pixel is which is where you start when you want to see how much dynamic range the sensor is capable of. Other factors add in from that point but a knowledge of size can be a useful measure.

Pixel size is also irrelevant. It is the size of the sensor , not the pixel, that matters, as well as the number of pixels. Of course, the lens also plays a central role, as does the efficiency of the sensor. But neither the pixel density, nor the pixel size, are a meaningful measure in terms of IQ.

I must be thick and don't understand basic mathematics.
This is my understanding:

All three things, sensor size, number of sensors and pixel density are all parts of the same mathematical equation and each part of the equation directly realates to the other.
Sensor size divided number of pixels gives you density.
Number of pixels multiplied by density equals sensor size.
Sensor size divided by density equals number of pixels.

How can they be separated so that two matter and one is irrevevant? From my understanding of basic mathematic formula what you are saying makes no sense.
Joe help us out here please

 

[Great Bustard]

This is my understanding:

All three things, sensor size, number of sensors and pixel density are all parts of the same mathematical equation and each part of the equation directly realates to the other.
Sensor size divided number of pixels gives you density.
Number of pixels multiplied by density equals sensor size.
Sensor size divided by density equals number of pixels.

Yes. But you need two of the measures to make any meaningful statement about IQ. Trying to reduce two independent measures into a single measure doesn't work.

The most natural measures are sensor size and number of pixels. But, for sure, we could instead use pixel size and sensor size, or sensor size and pixel density.

How can they be separated so that two matter and one is irrevevant?

Because the third measure is not an independent variable, it is computed from the two other independent measures.

From my understanding of basic mathematic formula what you are saying makes no sense.
Joe help us out here please

Well, gotta run (literally). Hope this makes sense. If not, feel free to press me further.

 

[Fish323]

This is my understanding:

All three things, sensor size, number of sensors and pixel density are all parts of the same mathematical equation and each part of the equation directly realates to the other.
Sensor size divided number of pixels gives you density.
Number of pixels multiplied by density equals sensor size.
Sensor size divided by density equals number of pixels.

Yes. But you need two of the measures to make any meaningful statement about IQ. Trying to reduce two independent measures into a single measure doesn't work.

The most natural measures are sensor size and number of pixels. But, for sure, we could instead use pixel size and sensor size, or sensor size and pixel density.

How can they be separated so that two matter and one is irrevevant?

Because the third measure is not an independent variable, it is computed from the two other independent measures.

From my understanding of basic mathematic formula what you are saying makes no sense.
Joe help us out here please

Well, gotta run (literally). Hope this makes sense. If not, feel free to press me further.

It does now. Your statement was very, very confusing. None of the elements is an independent variable, all 3 are related and each is as relevant as the other. It's like the speed, distance and time formula.

Any one can be the 3rd variable as I have shown you. It just depends how you look at it and what information you have available to you. Basic mathematical problem solving for 12 year olds.

 

[John Sheehy]

Sensor size divided number of pixels gives you density.
Number of pixels multiplied by density equals sensor size.
Sensor size divided by density equals number of pixels.

How can they be separated so that two matter and one is irrevevant? From my understanding of basic mathematic formula what you are saying makes no sense.

Maybe what he means is that as a sole parameter, it tells us absolutely nothing about the image potential. With just the pixel size, you have no idea how much resolution the sensor can have, or how much light it can collect. The number of MP gives you potential image resolution, alone, and the sensor size tells you how much light can be collected, alone.

--
John

 

[Lee Jay]

GB - You are right, of course, but I'd just like to add that pixel density is relevant to image quality when you are focal length or magnification limited and your goal is primarily detail extraction. In those cases, more PD is better. Yes, I realize you already know this.
--
Lee Jay
(see profile for equipment)

 

[Great Bustard]

GB - You are right, of course, but I'd just like to add that pixel density is relevant to image quality when you are focal length or magnification limited and your goal is primarily detail extraction. In those cases, more PD is better. Yes, I realize you already know this.

Indeed -- and that is an important clarification to make. Thanks!

 

[Fish323]

Maybe what he means is that as a sole parameter, it tells us absolutely nothing about the image potential. With just the pixel size, you have no idea how much resolution the sensor can have, or how much light it can collect. The number of MP gives you potential image resolution, alone, and the sensor size tells you how much light can be collected, alone.

But what he actually wrote was

'Anyway, moving right along, pixel density is an irrelevant measure in terms of IQ (image quality).'

Quite clearly that statement is wrong, which is why I was initally confused by his explaination. He understands it, and I understand it, but his explaination was so poor that it confused me and made no sense.

 

[Great Bustard]

It does now. Your statement was very, very confusing.

Sorry about that!

None of the elements is an independent variable, all 3 are related and each is as relevant as the other. It's like the speed, distance and time formula.

Well, sure, we can take that route, but measurements such as the physical size of the sensor, and the number of pixels on it, seem more "natural" to use as "fundamental" than the pixel density.

Another perfect example is focal length, aperture diameter, and f-ratio. To me, the focal length and aperture diameter are fundamental, whereas the f-ratio is computed as the quotient of those two quantities.

Any one can be the 3rd variable as I have shown you. It just depends how you look at it and what information you have available to you. Basic mathematical problem solving for 12 year olds.

Sure, you can take any two of the three measures as fundamental, and which of the two are the "natural measurements" is subjective.