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Colt-45 May 27, 2003 12:53 PM

The mega pixel myth?
Don't know much about this myself so i'll let the more experienced of you decide then you can tell me :D
It say's "for a fairly decent 8x10 you need 7.2 megapixels" if so then how does this work with the reviews saying you can get this size print at less resolution?

Grand Dizzy May 27, 2003 1:41 PM

The article is making two points.

1). It makes the point that megapixels are not as important as many people think they are.

Very true. The image quality of the camera is way more important. Most people would much rather have photos that look good, rather than photos that are higher resolution.

However, this doesn't mean that megapixels aren't important.

To people like me, the number of megapixels is very important. My friend's camera has 2 megapixels and mine has 4. If I zoom in on my photo I can see details that he can't - because I have twice as many pixels making up the image.

I very often crop my photos down so that the composition of the photo is better. If I crop half of the photo out, then the number of pixels has halved. It's very easy to end up with a very low resolution photo, but if you're working with a high enough resolution in the first place then you don't have to worry about that so much.

But... image quality is obviously a lot more important than resolution.

2) The article also makes the point that film is vastly higher resolution than most digital cameras.

This is another very true point. I've often heard it said that the level of detail of 35mm film is the equivalent to many thousands of pixels wide, and to get a resolution that matches 35mm film you'd need at least 15 megapixels.

However, that doesn't mean that you need 15 megapixels to take good photos, it just means that you need 15 megapixels if you want to get the same level of detail as 35mm film. But in most cases that isn't necessary.

A good 4 megapixel digital camera gives way, way better results than a bog standard 35mm camera. Well, mine does.

Don't worry about megapixels, just worry about image quality of the camera (like the article says). However, megapixels does matter to some people, and it is still fairly important in my opinion.

Colt-45 May 27, 2003 2:03 PM

Great reply Dizzy! it realy helps a beginner like me when someone like yourself answers what can be very basic questions, but when you are just starting out (and reading everything you can) all these answers help so much in getting a better understanding of these issues.

I remember not that long ago that I hated digital! because I saw it as competition to film (not that I use film that much :D ) but as I started reading about digital again just in the last week or so, I began to realise just how much fun these cameras can be, and now see them not as competition but as complimentary to film.

Thanks again for the reply


eric s May 27, 2003 2:14 PM

Lin Evans wrote a very good reply to a related question awhile back. I'll see if I can dig up the link. Ah, here it is.

What they asked was what MP is needed for a picture of size X by Y. You'll have to read Lin's full answer, but the question has a lot to do with what is in the picture. You're quote from the article is to get a "Decent 8x10 you need 7.2 MP". But decent picture of what? Some things really needs LOTS of detail (a landscape, for example) that only a higher resolution camera can give. I've seen some very nice pictures taken with a D100, which is only 6.1PM, printed at 16x30 or so. Beautiful view looking up into a backlit tree with the light coming through big fingered leaves. It didn't *need*7.2 MP.

I agree with Grand Dizzy:


Don't worry about megapixels, just worry about image quality of the camera (like the article says). However, megapixels does matter to some people, and it is still fairly important in my opinion.
Worry more that the camera offers the features you want, like manual settings or reasonable zoom and/or macro. That it fits well in your hands & good button placement. Is it a size you are willing to carry around (many people say "fit in my shirt pocket is required" others are happy with more features and a larger size.) If you don't have it with you or you fumble to when using it, it doesn't matter how many MP the camera has.

Colt-45 May 27, 2003 2:24 PM

Thanks Eric, more great help which I can realy use, I'll read that article as soon as I can, the thing I'm still confused over even after reading a lot about pixels and such is why can I display a very large image (in great detail) on my comp but I can't print it out at this size? I know it has something to do with the pixels and DPI and the monitor but still don't get it, (must be a simple solution to it)

Is there a standard ratio of pixels to inches that I can use to figure how big a image will be if printed out at that particular resolution?

Sorry again for the obvious questions, but I'm bound to understand it soon I hope! :D


PSknr May 27, 2003 2:49 PM

Thats pretty interesting reading, He has alot of good stuff on his website about the differences between digital and film. He seems not to be partial to one or the other, unlike many of the articles I've read. Some brag up digital, saying it will replace film entirely and others say digital is not even close to the quality of film so stay away from digital. I do have to agree with his article, but remember his biggest point is that the MP of the camera has little to do with the quality of the image. I think people get way to hung up on megapixels. We want a magic number that will tell us that digital is as good as film. Some digital cameras(even low MP cameras) are already better than film in some ways and in other ways not near as good.

lg May 27, 2003 2:50 PM

Take into consideration also the magnification of the image on the CCD. All other factors being the same, at full zoom, a 2MP camera with a 10x optical zoom will provide a better image than a 3MP camera with a 3x zoom even if the 3MP image is enlarged and then cropped.

Grand Dizzy May 27, 2003 7:49 PM

Colt, I'll try to answer your question of how come you can look at an image on a big computer screen and it looks fine, but you can't print it out at that same size...

The reason this is true is because you are dealing with multiple resolutions. (This may be a bit needlessly waffly, but it may help you understand things better.)

1) Photo resolution

First, you have the resolution of the photo itself. The photo may have been taken with a 10 megapixel camera and be very high resolution, or it may be a picture you grabbed from a web page, and be very low resolution. This is the resolution of the photo.

2) Screen resolution

Secondly, [this one only applies to looking at a photo on a screen] the screen is probably set to its own resolution. Such as 1024x768, or 1600x1200.

If you are looking at the photo at 100% zoom then your screen resolution will exactly match the photo resolution, because each screen pixel will directly correspond to one pixel of the photo.

However, if your photo is "bigger" than your screen and you zoom out to fit it all on screen, then you are not seeing each pixel of the photo, you are seeing a lower resolution representation of it. In other words, you will not be able to clearly see each of the dots that makes up the photo, you will see a lower res representation of it, using fewer dots.

3) Medium resolution

But as well as that, you have the resolution of the medium you are viewing the image on. This has nothing to do with the resolution of the photo, and nothing to do with the screen resolution.

Print outs have a "resolution". If you look at an image that has been printed out, then you are looking at a series of dots that make up the print. For inkjet printing, it's a simple grid of dots. For screen printing, it's several grids (usually 4) of different coloured dots all at different angles, so the pattern of dots is very complex.

But the resolution of all (or most) printers is very high. They are very fine and crisp, so if you print out a low resolution photo, then you will be able to clearly see all the little squares that make up the picture. And each of them will look square - because the level of detail of the print out is so high that the edges of the squares will be defined precisely. When all the pixels of an image are clearly visible as squares, the image is said to be "pixellated".

Screens have a "resolution". If you look at an image on a screen, then you are looking at a series of dots that make up the picture.

On LCD screens, it's a simple grid of dots that light up at different colours - the resolution of this grid is known as the "native resolution", and usually the screen resolution is set to exactly match the native resolution, so the pixels are extremely clearly defined.

LCDs are very neat in this respect, so the images are usually much crisper than other types of screen, and pixels look much squarer. (This can also be a drawback, because text often looks too pixellated.)

On all other screens, however (probably the type you're reading this on). The dots are not arranged in a neat grid. The images are made up of red, green and blue phosphor dots, and they're often placed in little triangles. They are not in any kind of grid - they do not correspond in any way to the resolution that the screen is set to (because screen resolution can be changed whereas the phosphors that light up to make the picture never change).

The red green and blue phosphors simply light up when pixels of the image overlap them. Usually you have several dots lighting up for each pixel of the image, and several pixels overlapping the same phosphor. There are usually about the same number of pixels as there are phosphor triads. Which means that you don't see a very precise prepresentation of the actual "screen".

What makes the resolution of your screen quite different from the reoslution of a print out is that your screen's resolution is much much lower resolution. It is not crisp, it is blurry in comparison. In a printed image, you will have loads of little dots making up the straight edge of a pixel, so you can see it's a straight, hard edge. But on a screen, the hard, straight edges inbetween pixels are not represented clearly. You just have a bunch of red, green and blue phosphors nearby that try to give the impression of a straight line, but the number of phosphors is very low.

If a screen had the same precision as a print out (ie if you could see the image clearly) then you would see the pixels and the image would be pixellated. And not look very good.

I'll try to think of an analogy...

Ah... I've got one.

You know those office toys with metal pins that you can push your hand onto and it will leave an impression of your hand?

Well imagine you push a Rubik's cube onto one of those. That is like a print out of a pixel. You can clearly see the straight edge of the square, becaus there are a lot of dots making up that "pixel".

But imagine you threw the rubik's cube onto one of those big toy pianos on the floor that light up when you stand on the keys. Maybe the rubik's cube would overlap two keys, and the key that it landed on the most lit up very brightly, but the other key that it only overlapped slightly lit up.

Now, you can still tell by looking at the piano that there is supposed to be a "pixel" there. You can see its exact size and position, but you can't see a representation of what shape the rubik's cube was. It's just a "blurry" dot.

I've thought of something else which should help explain...

The resolution of a TV screen is much lower than a computer monitor. The resolution of the image is low (usually about 576 pixels high, or 480 if you live in America). And accordingly, the resolution of the screens themself is low. The phosphor dots that make up a TV screen are much bigger than those on a computer monitor. If you look closely at a TV set you'll see the little red green and blue phosphor dots clearly.

But here's the point... if you look at a very low resolution picture on your TV set (576x432) it will appear perfectly smooth and crisp because the screen's phosphors are at a low resolution.

But if you look at such a low resolution on image on a computer monitor, which has a much crisper display, then the image will look horribly pixellated.

You get this effect when you try and play a console game on your PC. The graphics look blocky.

I've written far too much here. But hopefully you will appreciate it because you seemed to appreciate my first reply.

Hope you got the point beind all that. If not, ask.

BillDrew May 27, 2003 11:08 PM


Originally Posted by lg
Take into consideration also the magnification of the image on the CCD. All other factors being the same, at full zoom, a 2MP camera with a 10x optical zoom will provide a better image than a 3MP camera with a 3x zoom even if the 3MP image is enlarged and then cropped.

True only if you are interested in shooting with a long lens. I tend to want a short lens, and have had to figure out how to stitch images to get that - the hard way of doing it. That is one clear example of no single answer being right for everyone.

Lots of good info in the posts here, and the link you have has at least the idea of resolution going as the square root of pixel count right. Beyond that, the question of how many pixels are needed to print an 8x10" is pretty much the same as the question, "How high is up?"

Lots of folks will claim to have the answer, but it really depends on things like where you live. If you live in the mountains, or in a city like New York, you will have an altogether different idea than if you live in the flats of Kansas where "up" is anything higher than the silo. Just about everyone will admit that "up" is higher than the bottom of their feet, and not many would deny that the orbit of Neptune would be far enough to be called "up".

Comes down to you having to figure it out to suit yourself and what you are trying to do.

eric s May 27, 2003 11:15 PM


Is there a standard ratio of pixels to inches that I can use to figure how big a image will be if printed out at that particular resolution?
This is not an uncommon question. It's usually phrased as what is a good "dots per inch" for a picture you want to print. This directly effects how large a picture you can print, but it isn't the only factor (read Lin's post.)

A picture has a fixed resolution (3088 x 2056 for the 10D at 6.1MP, but a more reasonable number is 2272 x 1704 of the Nikon 4500 @ 4MP.) But you choose how bit a print out you are making. Are you spreading those pixels over 12x24? Or 4x6?

That leads to a value of "dots per inch"... how many pixels of the picture are used to make a single inch on paper. If you don't have enough data per inch, the picture will (probably) look bad. But "how much is enough" is a combination of personal preference, the printer, and the subject (among other things.) Many people will quote 300 dots per inch, others say 150.. a few will say even less. After you read that post by Lin, then read this one by him as well:

Technically, it's about upsampling/interpolation algorithms. But the pictures he puts in the post shows some news paper pictures. They are very low "dots per inch" but it's clear what the larger picture is of (people.) But if you blow up the picture too large (the lower example) there is too few dots per inch, and it doesn't look much like the person's face any more.

You'll find that it depends on your picture, your camera and your printer. So try it out. Take a picture and print it at different sizes. See what it looks like. In the end, that is the final judge. I wouldn't go below 70 or so DPI... but I bet even that would work in some situations (like news print? Or a billboard at 200 feet?)

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