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Old May 17, 2011, 12:43 PM   #1
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Default Does picture quality go down as megapixels go up?

I am a novice at taking pictures, and plan to just use simple point and click cameras for the rest of my life. I don't need hi-res pictures. I never print pictures. In fact, on my current camera, which I think can do 8 megapixels, I have it set to only take 3 MP pictures, since they take up less hard drive space. I am thinking of buying a new camera, and all the newer models seem to be 12 MP or higher. I read somewhere that if you are taking a 3 MP picture, it will be better quality if you have a 3 MP camera, compared to having a 12 MP camera that is set to only do 3 MP pictures. This is because the chip size hasn't increased, or something like that. Is this true?

Thanks for you wisdom!

P.S. I have unrelated question: on newer cameras that have image stabilization, does the IS work for both still pics and movies?
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Old May 17, 2011, 1:18 PM   #2
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What matters is where the downsampling happens, and how many times it happens.

If you only ever display your photos on your computer or television, then anything larger than 2 megapixels is a waste. If you have your 8MP camera record 3MP images and display them on a 2MP screen, you'll probably end up with poor image quality. The reason is that the camera doesn't have a lot of processing power, so it probably uses a simple (and not very good) downsampling algorithm. Then you downsample them again when you display them on your computer or TV. The computer probably uses a very good downsampling algorithm, but it's starting with a (poorly) downsampled original, so the result won't be very good. The TV probably has another simple (and not very good) downsampling algorithm, so you'll see a poorly downsampled version of a poorly downsampled image.

If you kept the image size at 8MP, then the camera won't do any downsampling, and the computer will have a much better image to work with when it downsamples, as will the television, though it will have more work to do and so will probably take a lot longer.

And remember that both your computer and your television can zoom in. If you only provide them with 3MP images to work with, they'll have to upsample those previously downsampled images, and the results will not be pretty.

Ideally, you'd only do the downsampling once, and use the computer to do it (not the camera.)

This is simple enough to check.

Take a photo at full resolution. (Outdoors would probably be better, containing grass, trees, and other foliage and detail.) Then, take the same photo at each of the other resolutions that your camera provides. Then view the images on your computer. See which images have preserved the detail best. Then, zoom in, and see which images have preserved the detail best. Then do the same thing on your television.

This will give you first hand experience on how different image settings are affected by your camera settings.
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Old May 17, 2011, 2:19 PM   #3
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This is true to an extent. The real thing is that whatever camera you have, you get the BEST image quality if you snap at the censor's inherent resolution. I have a Panny Fz40. The tag on it shows 14MP. However a picture snapped at 14 MP has a chance of actually being worse than one shot at something around 9-10 MP because the censor in my cam is 9.8 MP. I hope that answered your question

And as for IS, yes, you get that for both still and motion
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Old May 17, 2011, 4:58 PM   #4
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Quote:
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... I have a Panny Fz40. The tag on it shows 14MP. However a picture snapped at 14 MP has a chance of actually being worse than one shot at something around 9-10 MP because the censor in my cam is 9.8 MP. ...
The specifications that Panasonic published for the FZ40 state that the image sensor is "1/2.33-inch / 14.5 Total Megapixels / Primary Color Filter", with 14.1 effective megapixels.

Are you saying that Panasonic's published specifications for the FZ40 are wrong?
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Old May 17, 2011, 5:08 PM   #5
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So a couple follow up questions:

1. If I am planning on only doing 3 MP pictures, would the picture quality be better with a 3 MP camera than using a 12 or 8 MP camera but using the 3 MP setting? Would a 12 MP camera on the 3 MP setting have worse quality than an 8 MP camera on the 3 MP setting?

2. If I have a camera where the sensor's inherent resolution is 8 MP and have it on the setting to take 3 MP pics, does it take a regular 8 MP pic and then downsample it to a 3 MP pic?

3. If the purported max resolution is not the same as a camera sensor's inherent resolution, do the specs usually say what the inherent resolution is? I don't remember seeing that when looking at different models.

Thank you for your responses!
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Old May 17, 2011, 6:41 PM   #6
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First, I think xHassan is mistaken about the true resolution of the image sensor in his FZ40.

Second, if you'll always be displaying your images on a 2MP output device (a computer monitor or television), then, if you can't downsample your images to 2MP in the camera, then use the greatest resolution your camera can do, so the downsampling algorithm (in the computer or the television) has the most data to work with. Downsampling a full resolution image will always be better than downsampling a previously downsampled image. Plus, if you want to zoom in, you can.

To be clear, what you read is wrong.

But if you really don't want to handle all those big image files, then you could stick with the 3MP images, or you could go with 5MP instead. The files would be bigger than the 3MP images, but not as big as the 8MP images. Plus, you'd have something to zoom into if the occasion arose.
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Old May 17, 2011, 6:53 PM   #7
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1. Theoretically, if the sensors are the same physical size, you would have better dynamic range and less noise with a 3MP sensor. (all other things being equal, which of course, they're not) You probably won't find a (new) 3MP camera these days, though.

2. Usually, yes. This is not necessarily bad, though, as the downsampling averages out some of the noise, and you may end up with a cleaner looking picture, though sharpness may suffer a bit.

3. The camera isn't going to have more resolution than the sensor. Very often there is an area of the sensor which isn't used, though- the outermost rows of pixels are sometimes not included in the camera's resolution. The specs might say 8MP effective resolution from a 8.2MP sensor (for example).

Overall, it really is not worth worrying about. For all practical purposes (such as the way you view the photos), there won't be any discernible difference unless you are in the habit of zooming in on details.

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Old May 17, 2011, 11:28 PM   #8
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Quote:
Originally Posted by TCav View Post
The specifications that Panasonic published for the FZ40 state that the image sensor is "1/2.33-inch / 14.5 Total Megapixels / Primary Color Filter", with 14.1 effective megapixels.

Are you saying that Panasonic's published specifications for the FZ40 are wrong?
If you refer to the Nikon website for the Nikon P100, the censor size is the same as that for the Fz40 and the effective MP it has to offer is 10.3 MP. Since the pixel size remains same whatever the censor is, for a censor of the same size, the TRUE resolution is the minimum of all the MPs tagged. So imho, the TRUE res of this camera is 10. something. The extra 4 is extrapolation. That is why you will notice that you get the same amount of detail (at times worse) at the mentioned MP and at the true censor res
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Old May 18, 2011, 3:42 AM   #9
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Quote:
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If you refer to the Nikon website for the Nikon P100, the censor size is the same as that for the Fz40 and the effective MP it has to offer is 10.3 MP.
Many cameras use image sensors of that size (1/2.33"). The 12.1MP Pentax X90, 14MP Olympus SP-800UZ, and 14MP Kodak EasyShare Z981 are some examples. Each of those manufacturers claims 12.1, 14, and 14 megapixels effective resolution, respectively, for their cameras. Are you suggesting that they are all misrepresenting their products?

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Since the pixel size remains same whatever the censor is ...
Pixel density has been steadily increasing since the advent of digital image sensors.

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Originally Posted by xHassan View Post
... for a censor of the same size, the TRUE resolution is the minimum of all the MPs tagged. So imho, the TRUE res of this camera is 10. something.
With steadily increasing pixel densities, the actual number of photoreceptors on image sensor, and thus the true resolution of those image sensors continues to increase. As the resolution of image sensors has increased over the years, there's no reason to suspect that image sensor resolution hit an insurmountable obstacle at 10MP, and hasn't been able to make image sensors with higher resolutions. Are you suggesting that there is?

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The extra 4 is extrapolation.
If the extra 4MP is simply extrapolated from the true 10MP, why stop there? If it's just math, why wouldn't camera manufacturers put more powerful microprrocessors into their cameras, and extrapolate an extra 6. 8, 10, heck, 20MP out of the true 10MP?

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That is why you will notice that you get the same amount of detail (at times worse) at the mentioned MP and at the true censor res
Actually, I haven't noticed that.

I think you've got it wrong.
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Old May 19, 2011, 9:46 AM   #10
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I am not in a position to say that they are misrepresenting in that sense. They claim 14 MP and you GET an image having a resolution of 14 megapixels.

The point I'm implying is that they are not 14 million receptors that have translated the visual information. 'Effective' is what you get. Whatever the receptors give, you process them to your required resolution.

As for the extrapolation WHY you won't jack up the res like that? It's EXTRApolation. Each pixel is replicated as an average of all the surrounding pixels. The more you extrapolate, the more inaccurate information you force into the image. To get a picture of what I am saying, take a picture and zoom it up to 200%. THAT is what will happen to an extrapolation of 10MP to 20MP....
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Last edited by xHassan; May 19, 2011 at 9:52 AM.
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