Digital camera question

[squeekster]

I have an HP 2.1 megapixel camera. Nothing fancy. I'm not really into fancy anyway. But would I gain anything by getting a camera with higher megapixels? I probably wouldn't enlarge anything to bigger than 8 X 10. With the camera I have now, when enlarging to 8 X 10, the pictures seem to be a bit grainy, although not terribly so. A clerk in the camera dept. of the local WalMart said that all I would gain from a higher megapixel camera was the ability to have sharper BIG pictures (8X10 and up) but a higher megapixel camera would gain me nothing for regular shapshot sized pictures. That sounded somewhat fishy to me, but then again, what I really know about all this could easily be fit on the head of a pin. So I will turn to the people that *really* know the straight dope. What say you? Thanks.

[Mr. Blue Sky]

A digital camera FAQ explaining your question.

BTW, would your camera happen to be the HP 315?

[squeekster]

Originally Posted by Mr. Blue Sky

A digital camera FAQ explaining your question.

BTW, would your camera happen to be the HP 315?

Thanks for the link.

No, it is a Photosmart 635 just like the one reviewed here, but I don't have one of those dock things.

[Finagle]

Originally Posted by squeekster

A clerk in the camera dept. of the local WalMart said that all I would gain from a higher megapixel camera was the ability to have sharper BIG pictures (8X10 and up) but a higher megapixel camera would gain me nothing for regular shapshot sized pictures. Thanks.

Well, the clerk was mostly right (although I'm not sure where the cutoff lies in getting better 4x6 prints -- I'd guess it to be a bit higher than 2.1Megapixels, but not much). However, more megapixels gives you more ability to crop your pictures before printing them without losing details. So unless you're a whiz at framing pictures and have all the zoom range you need on your camera, you'll probably run into the occasional situation where those extra pixels will help.

[Padeye]

There are a lot of incorrect assumptions about megapixels, one being that more is always better. This is true if the sensor is proportionally larger but often putting more photsites onto a smaller sensor results in a worse signal to noise ratio and poorer dynamic range.

That said a 2.1mp camera is on the bottom end of the range for printing at 8x10. You might see slightly better detial from a 3-4mp camera with a similar size sensor but diminishing returns beyond that and little ability to crop and maintain detail.

[WonJohnSoup]

Since the OP got answered quickly, I got something that might help both of us.

So if the megapixels is a high number, does it benefit any when you resize the picture down so the whole thing fits on your screen (without cropping anything out)? Or does your monitor display a certain resolution dimension and all it does is start throwing away pixels? In other words, does a, say 5x5inch picture on my screen contain the same amount of pixels no matter how many megapixels it started out with?

Cuz an 8 megapixel picture resized seems a bit sharper than a 2 megapixel resized to me, but that may have been the larger sensor the 8-MP picture came from to start with. And do different monitors actually have higher resolution or are the pixels just bigger to start with?

Basically, in terms of just displaying on the web, is megapixel like the top speed on your car, as in it doesn't help much beyond a certain number?

[WonJohnSoup]

Now that I finished typing, I think finagle may have answered my question. Confirm?

[Cheesesteak]

Conceptually, each print you make today is made up of 2 million individual dots. In a 4x6 each dot is a certain size, in an 8x10 each dot has to be bigger to fill out the bigger overall area. If the dots in the 8x10 are just barely large enough for your eye to see directly, that would make the 8x10 appear grainy while the 4x6 is not.

Going to a 4 megapixel, for example, would break the 8x10 up into twice as many dots, each half the size of the old dots, and too small for your eye to perceive individually. The graininess is gone. In the 4x6, the dots were already small enough to make a quality print, so the extra pixels do not offer improvement.

As was mentioned, though, megapixels are not the only measure of quality. You would probably get better 8x10 prints from a very high quality 3.2MP than you will from a lower quality 8MP.

[Fear Itself]

The usefulness of higher resolution is not limited to enlarged print size. Higher resolution pictures can be cropped and enlarged without pixellating. This allows you to improve pictures that were not composed well when they were taken, yet still create prints that are large enough for your needs.

[Telemark]

Originally Posted by WonJohnSoup

Basically, in terms of just displaying on the web, is megapixel like the top speed on your car, as in it doesn't help much beyond a certain number?

To an extent, this is true. Your monitor is 72 DPI. If you image has more than that many pixels to display (which is true at most usual web/email sized images) than those pixels are not going to make the image any clearer.

However, you can crop to a corner of the original photo and still get a similar sized and quality image if you start with more MP.

For an 8x10, in general, you're not going to get any higher quality print once you past the 5 MP image size. But with a bad lens, electronics, or CCD you can get bad quality 5MP images; some cameras are better than others, even if they have lower image size.

And with the same CCD size, you can try to cram too many pixels and end up with "noisy" images. Sometimes fewer MP can produce better images as well.

[Padeye]

Originally Posted by WonJohnSoup

So if the megapixels is a high number, does it benefit any when you resize the picture down so the whole thing fits on your screen (without cropping anything out)? Or does your monitor display a certain resolution dimension and all it does is start throwing away pixels? In other words, does a, say 5x5inch picture on my screen contain the same amount of pixels no matter how many megapixels it started out with?

This depends entirely on the software displaying the image. There are many methods to downsample an image and not all produce the same quality ouput. "Throwing away" the extra pixels is generally the worst and often results moire patterns and the loss of detail that shold be apparent even at the lower resolution.

Originally Posted by Fear Itself

The usefulness of higher resolution is not limited to enlarged print size. Higher resolution pictures can be cropped and enlarged without pixellating. This allows you to improve pictures that were not composed well when they were taken, yet still create prints that are large enough for your needs.

This is another tricky one since linear pixels per inch is the square root of total pixels.

Say you're using a 3mp camera, 2048x1536 pixels, to print an 8x10. That's 192 pixels per inch which is quite reasonable for printing. If you want to crop a 4x5 section and print it at 8x10 you are now at 96 pixels per inch which is not so good. This is barely above screen resolution and pixelization will be apparent with a high resolution printer. If you want to cure the problem with a higher pixel count camera you'll need a 12mp camera to equal the same print quality.

The problem is they won't be equal. If the same small size sensor is used you'll have half as many photons per pixel when capturing the image but the same inherent noise in the sensor. This means more random noise and less dynamic range, the ability to record a range of light to dark.

I've had experience with 5mp cameras using a 2/3" sensor - the largest sensor used on consumer cameras. Noise problems were horrendous. There are even higher pixel count cameras with even smaller sensors now and they mask the noise by heavily processing the images which unfortunately removes any extra detail the extra pixels were supposed to record in the first place.

[Mangetout]

As well as cropping and enlarging, I think you will find that some effects filters applied in software will just work better, because they would be working upon a source with a higher sampling rate