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Old Nov 20, 2010, 4:04 PM   #1
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Default Relationship between sensor size, number of pixels, and image detail?

Is there a good explanation of the significance of sensor size when it comes to p&s digicams?

I've gotten the impression that sensor size has more to do with IQ than the number of pixels, but I'm not sure I understand why. Are the "pixels" on a sensor actually physical entities or some kind of analog-to-digital conversion?

I can't say how many times I've seen very large "original size" photos on the internet that looked like it used an excessive number of pixels to define the image. On the other hand, many photos seem to have far more detail defined by far fewer pixels. Is there a correlation there between sensor size and the number of pixels? Or is it totally unrelated and nothing more than expanding a smaller image to a larger field?

If pixels are little more than a way of digitally mapping out an analog image, I'm curious about my the Canon Powershot S70 I've had since '04 that has a larger sensor than many I see today. If sensor size is an important factor, could I still get superior pictures from that 7.1 megapixel camera than many of the newer 12 or 14 megapixel cameras with smaller sensors?
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Old Nov 20, 2010, 5:22 PM   #2
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The resolution of (the number of photoreceptors in) the image sensor determines the level of detail in an image. Digital image sensors are made up of a grid of photoreceptors that collect light and turn it into electrical charges. The more light a photoreceptor collects, the higher the voltage it generates, and so the brighter the corresponding pixel will be in the resulting image.

The physical dimensions of the image sensor don't directly affect image quality.

If all you do is print 4x6 prints or display images on your computer screen or television, then the extra resolution of a newer digital camera will probably be wasted. The extra resolution comes in handy for producing larger size prints.

I hope this answers your questions.
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Old Nov 20, 2010, 7:10 PM   #3
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This is a fun subject, and the source of a lot of argument. When you start talking about image resolution, you wind up with an argument. For example: I take exception to TCav's statement that sensor dimensions don't affect image quality. A digital sensor consists of a number of photosites separated by a grid - like looking through a screen. For a given number of pixels (holes in the screen), the larger the size of the screen, the smaller the percentage of wires, allowing you to see more through it. This argues in favor of larger sensors.
When you view a picture, you aren't seeing it at the same relative size, for different formats. To print an 8x10 inch photo from a small sensor digicam, you have to magnify it up to 7 times more than from a 35mm size sensor. This certainly affects image quality. If viewing on a monitor, consider that for example, a pixel on a sensor may be 2.5 microns wide, and an a monitor, .25 millimeters - a hundred times larger. Small distortions and edge effects from AA filters, etc, become much more visible.

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Old Nov 20, 2010, 7:30 PM   #4
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Quote:
Originally Posted by TCav View Post
... The physical dimensions of the image sensor don't directly affect image quality. ...
Quote:
Originally Posted by VTphotog View Post
... I take exception to TCav's statement that sensor dimensions don't affect image quality. ...
I didn't say that a sensor's dimensions don't affect image quality. I said that a sensor's dimensions don't directly affect image quality. And even the indirect effects of a sensor's dimensions on image quality don't affect it as much as other factors that are unrelated to a sensor's dimensions. And none would degrade image quality as much as increasing the resolution would improve it.

My point is that the benefits of increased resolution are lost if the image is only ever displayed on a low resolution output device. And if an image is displayed on a high resolution output device, a higher resolution image from a smaller image sensor will look better than a lower resolution image from a larger image sensor.
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Old Nov 20, 2010, 9:38 PM   #5
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This is quite helpful.

In early '08 I replaced my S70 - which has a 7.1 MP 1/1.8" CCD - with a Canon SD890IS, which has a 10 MP 1/2.3" CCD.

I really love the SD890IS - which has a fairly decent 3.2 aperture lens as well, but unfortunately I need to replace it as it no longer focuses properly on a consist basis. It seems that something inside the lens assembly may be jumping a geartooth or something when the zoom is utilized.

Whatever the case, I'm hoping to find a next p&s that will at least give me most of the great functionality and IQ I had grown accustomed to.

I actually bought a Panasonic Lumix ZS6 at Costco to give a try. While its video capabilities blow me away for a compact camera, I've been quite disappointed with the lack of detail and clarity I'm getting on indoor shots in comparison to the pictures I'm accustomed to with my S70 and SD890IS. Could this be at all attributed to the smaller sensor size of the ZS6?
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Old Nov 21, 2010, 3:29 AM   #6
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There are lots of possible reasons for the problems you mention. Can you post some examples of photos you're not satisfied with.
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Old Nov 22, 2010, 3:44 PM   #7
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I took a no-flash handheld low light picture with each of two cameras (my '08 Canon SD890IS and a new Panasonic Lumix ZS6) a couple days ago and noticed a big difference in what each camera did with the scene. I didn't do any tweaking of the camera settings - just turned off the flash and did a point, frame, and shoot. The SD890IS that is no longer focusing consistently when zoomed took the picture represented by the first two attachments. The first is the original photo resized to 1024 x 768 and the second is a 1024 x 768 pixel-for-pixel crop.

I don't have the ZS6's photo with me at the moment but will try to post it tonight. My hope is that my next pocketable camera will be able to take non-flashed handheld pictures about as well as this one by the SD890IS.
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