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Old Aug 24, 2006, 11:07 PM   #1
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I`ve posted elsewhere that I am on the verge of purchasing a camera, and I just have a few questions about megapixels.

The cameras I am considering are all between six and ten megapixels. The first part of my question is pretty basic and purely practical. If I want to make a large print, how large can I make it with a six MP camera? How large can I make it with a 10 mp one... Of course, I mean without losing quality.

Secondly, I:ve read that having more mps means having smaller censors in the camera, which can result in more noise. My question relating to this is purely theoretical: if the above is the case, why don:t they use the high end technology that is presently used on ten mp sensors and apply it to 6 mp cameras... wouldn:t you get wicked iso performance this way?

Finally, I have one last question. Take a six mp camera and a ten mp one. Now, set the settings on the tenner to six mps (I am assuming you can do this). How do the pics of either camera compare in this scenario?

Thanks for your time,

- Bpp
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Old Aug 25, 2006, 10:46 AM   #2
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Ballpointpenner wrote:
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how large can I make it with a six MP camera? How large can I make it with a 10 mp one... Of course, I mean without losing quality.
Take the largest dimensions (in pixels) of each, and divide them by 300. That gives you 300 pixels per inch. That's usually print-ad/magazine quality pics. For photograph, you can usually get away with less (as low as 150ppi or less) depending on what the image is. If there's a lot of edge-boudaries, like foliage, you probably need high pixel density, if it's something relatively flat, like a building or most portrait then you can get away with less. In general, with 6MP, you can print at least 2 by 3 feet. Note that there is a difference between a camera's pixel quantity and quality.

Another thing people ignore is viewing distance. If you print something that's huge, I hope you don't expect people to view it two inches from their nose. From what I've read, normal viewing distance is around the diagonal measurement of a photo. So on a 2 by 3 feet, that would be 3.5 feet.


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Secondly, I:ve read that having more mps means having smaller censors in the camera, which can result in more noise. My question relating to this is purely theoretical: if the above is the case, why don:t they use the high end technology that is presently used on ten mp sensors and apply it to 6 mp cameras... wouldn:t you get wicked iso performance this way?
Perhaps. But in general, consumers are suckers for high MP count because they don't know what it means and what they give up. Same goes to Zoom X numbers. So camera makers want the highest numbers and more checkboxes out there.

There are cameras that were purposely design with lower MP count but made for speed and image quality esp at high ISO, the Nikon D2H comes to mind.



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Finally, I have one last question. Take a six mp camera and a ten mp one. Now, set the settings on the tenner to six mps (I am assuming you can do this). How do the pics of either camera compare in this scenario?
Can't really comment on this since there are other variables involved. Remember that MP count is nothing more than quantity (ie, amount) of pixels. The QUALITY of those pixels is separate from that, and each camera will produce them differently.

In general, or let's say the two are the same camera with different MP count, the 6MP will produce better image at higher ISO. If it's different cameras, and depending on how old it is, the 10MP may have features that the 6MP doesn't have.

I have friends in this situation. THey own the same camera line, Canon SD's. It's the same camera, except one paid $150 more for more MP count. But he never uses it at high MP because the files are too big. He also never make prints, he just views it in his PC.


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Old Aug 25, 2006, 10:59 AM   #3
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For a direct comparision in the print size limitations and resolution gain between cameras you can use my calculator here: http://www.mattspinelli.com/mpcalc.html

Please also read my instructions and disclaimer as well.

Keep this in mind though. How big you can print isn't just limited to pixel count. For one the subject matters. As the above poster said detailed scenes require more pixels per inch than less detailed images.

But also equally important (if not more important) is how well focused the picture is. You can have a 10 MP image but if the focus is slightly off it may not look as good as a 6 MP image with the focus nailed. Just something to keep in mind.



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Old Aug 25, 2006, 4:09 PM   #4
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I:ve read that having more mps means having smaller censors in the camera, which can result in more noise. My question relating to this is purely theoretical: if the above is the case, why don:t they use the high end technology that is presently used on ten mp sensors and apply it to 6 mp cameras... wouldn:t you get wicked iso performance this way?
I'm not sure they haven't pretty much done that. Some of the newest small cameras on the market use a Sony 6Mp 1/2.5 sensor that seems to have pretty good noise characteristics. And of course the Fuji 6Mp 1/1.7 sensor is superb.

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Take a six mp camera and a ten mp one. Now, set the settings on the tenner to six mps (I am assuming you can do this). How do the pics of either camera compare in this scenario?
Cameras use the entire sensor and just downsample for a smaller output. If it is noisy at 10Mp it will be noisy if you extract the image at 6Mp. Better to get the 6Mp sensor in the first place if that is the output you want.

Noise and noise reduction costs you in resolution. But a 10Mp camera is probably going to give a better very large print than a 6Mp with the same sized sensor assuming an equal quality lens. There is a lot you can do in post processing if the camera itself doesn't mess up the image too much with in-camera noise reduction. You can selectively remove noise from shadows and flat areas like sky without deteriorating the resolution of the edges.

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Old Aug 27, 2006, 9:35 PM   #5
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Thanks for the answers guys. If six mp does 2 by 3 feet, thats plenty big for me. Since it is also likely to produce lower noise, thats probably what I`ll go for.

-- Bpp
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Old Aug 28, 2006, 11:14 AM   #6
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Ballpointpenner wrote:
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If six mp does 2 by 3 feet, thats plenty big for me.
The best 2 X 3 foot crop you can get from a 6Mp image (from a 4:3 camera) is 78 PPI. That is very poor quality unless you view it from across a room. I got a noticeable improvement in 13 X 19 inch prints going from 5 to 7Mp. If you want to make prints that large go with 10Mp and learn some sophisticated post processing including noise reduction, sharpening and resample.
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Old Aug 28, 2006, 12:13 PM   #7
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Ballpointpenner wrote:
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Secondly, I:ve read that having more mps means having smaller censors in the camera, which can result in more noise. My question relating to this is purely theoretical: if the above is the case, why don:t they use the high end technology that is presently used on ten mp sensors and apply it to 6 mp cameras... wouldn:t you get wicked iso performance this way?

More megapixels is not really about sensor size, it is the amount of megapixels that a given sensor has, be it large or small. If we compare two identically sized sensors and make one 6MP and the Other 10MP, it means the 10MP will have more pixels but they will be smaller in size. Smaller pixels don't capture as much light and the end result is higher noise. The advantage to having more megapixels is higher resolution. So, if you follow my logic than when comparing the megapixel rating of two cameras, it is important to compare like size sensors. For example, you cannot compare the 6 megapixel on my compact point and shoot with the 6 measgpixel sensor on my DSLR. Both are 6 megapixel cameras, but my DSLR does much better in low light because it is a larger sensor, which means the individual pixel size is larger and it captures more light and reduces noise.
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Old Aug 28, 2006, 2:41 PM   #8
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Dont worry about "megapixel generalizations". Generally more megapixels means a larger print, but what if the quality of your pixels is low? Generally more megapixels means that get more noise, because the sensor size is the same so each pixel is smaller therefore your signal to noise ratio is worse, but what if the camera's software is good? Generally, the only reason the word megapixel exists is because some slimy ------ in some marketing department ten years ago thought it sounded catchy. And it was.


There are technological differences and specific quirks that make these generalizations meaningless often. Its best to ignore pixel count altogether and compare each camera side-by-side by viewing the symptoms of sensor design, not the technical specifications. In other words, review actual prints/images.


You could generalize that 300 pixels per inch is required for a super high quality print, or that 180ppi is acceptable, but in truth you often need less pixels per inch as the print gets bigger because you view it from farther back. General consensus seems to be that 6mp is fine up to 13x19 inch prints. Add about 1.5 inches for 10mp. Its almost no different at all, in practical use, unless you make a bunch of big prints. Files will be bigger, though. Sometimes you can make a 30x40 inch print from a 1mp image and have it look spectacular. There are many, many, MANY variables.

The most relevent metric is that quality 6mp images (such as those from a DSLR) reproduce as well as 35mm film, including enlargments to large sizes. If you wouldnt consider using medium format film, then you probably shouldnt consider using a higher resolution camera unless doing so is absolutely trivial, but due to finances and quantum physics it never is.

The smallest photosite you want is 6-8 microns (due to physics, noise, etc). APS sensors are 16 x 24 mm, therefore should be 6 to 10 megapixels. Full frame sensors are 24x36mm so should be 13 to 24 megapixels. Any larger resolution should be a huge red flag that your buying a low quality sensor such as those put in compact cameras. Thier photosites are TINY, and their quality low as a result, not what you want in an SLR.
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Old Aug 28, 2006, 8:23 PM   #9
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OK,

I now more confused than I was to begin with, though this is probably a good thing. At this time, rather than trying to go further in understanding the theory, I have some more practical questions.

For the record, I am looking to buy a DSLR. One of the factors which prompted me to post this was that I had been reading on a different thread how the D50s 6mp censor was heads and tails ahead of its competitors (whether higher mp or not)in terms of picture quality, though this difference was easiest to percieve in long exposure shots. Though I know that this is going off topic, I:d like to ask whether this is actually the case or not?

In particular, my intention is indeed to make large prints, two by three feet is a good ball-park, so iq is an issue.

tmoreau,

Admittedly, most of that went over my head. So the practical difference between 6 and10 mp is only about 1.5 inches each way?! To be honest, thats far less than I expected. If thats the case and picture quality is a possible sacrifice than 6mp is surely the way to go. Is the difference in print size really so small?

Also, the point that you necessarily view a large print from further back seems debatable to me -- after all it depends on how it was meant to be viewed.

Slipe,

You seem of the opinion that more mps would indeed be handy for prints the size that I am considering. Was your experience with dslrs or point and shoots?

- Bpp


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