How many mega pixels do you need to achieve a quality image?

[punchkin]

.000001 at a minimum, if you want a high-quality 1-pixel-square image.

 

[Fardor]

methink the quality of an image... the overall quality of an image... depends more on what it's of than anything else. a colorful shot of some beach you haven't heard of or something is nothing compared to a cameraphone shot of you with your friends a long time ago, etc...

yeah, I know I'm talking about something else.

 

[dblevitan]

I recently printed some 6MP shots (Nikon D70, 18-70 AF-S) at 16x20 (slightly cropped since that 5:4, not 3:2). Both shots are high quality, even at web resolution (see here and here). They were printed by Mpix.com, one of the most highly regarded printers around.

Even though 16x20 is stretching it for 6MP, the prints look gorgeous. The only way you can even see any blurring is by standing 5 inches away from the print and examining one small area. Then you can notice that it's not perfectly clear. Otherwise, I can't complain about them and since one normally does not stand 5 inches away from a 16x20 print, I don't see this as an issue.

Also remember that when you double the number of pixels, you're actually increasing the resolution in each dimension by only the square root of 2 (roughly 1.4). So doubling the number of megapixels only gives you a 40% increase in each dimension.

 

[soydios]

Originally posted by: dblevitan
I recently printed some 6MP shots (Nikon D70, 18-70 AF-S) at 16x20 (slightly cropped since that 5:4, not 3:2). Both shots are high quality, even at web resolution (see here and here). They were printed by Mpix.com, one of the most highly regarded printers around.

Even though 16x20 is stretching it for 6MP, the prints look gorgeous. The only way you can even see any blurring is by standing 5 inches away from the print and examining one small area. Then you can notice that it's not perfectly clear. Otherwise, I can't complain about them and since one normally does not stand 5 inches away from a 16x20 print, I don't see this as an issue.

Also remember that when you double the number of pixels, you're actually increasing the resolution in each dimension by only the square root of 2 (roughly 1.4). So doubling the number of megapixels only gives you a 40% increase in each dimension.

You bring up two good points:

1) Extra resolution really just gives you more cropping leeway once you get past six or eight megapixels.

2) A doubling in megapixels results in at least a halving of photosite microlens size, thus dropping a stop of sensor noise performance. But that significant drop in noise performance only gets you a 41% improvement in linear resolution.

 

[punchkin]

Originally posted by: soydios

Originally posted by: dblevitan
I recently printed some 6MP shots (Nikon D70, 18-70 AF-S) at 16x20 (slightly cropped since that 5:4, not 3:2). Both shots are high quality, even at web resolution (see here and here). They were printed by Mpix.com, one of the most highly regarded printers around.

Even though 16x20 is stretching it for 6MP, the prints look gorgeous. The only way you can even see any blurring is by standing 5 inches away from the print and examining one small area. Then you can notice that it's not perfectly clear. Otherwise, I can't complain about them and since one normally does not stand 5 inches away from a 16x20 print, I don't see this as an issue.

Also remember that when you double the number of pixels, you're actually increasing the resolution in each dimension by only the square root of 2 (roughly 1.4). So doubling the number of megapixels only gives you a 40% increase in each dimension.

You bring up two good points:

1) Extra resolution really just gives you more cropping leeway once you get past six or eight megapixels.

2) A doubling in megapixels results in at least a halving of photosite microlens size, thus dropping a stop of sensor noise performance. But that significant drop in noise performance only gets you a 41% improvement in linear resolution.

Not quite. The difference printing from a 5D at 16 X 20 is very noticeable when compared with output from a 6 MP camera (haven't tried it with a D40, but with a Canon).

In addition, a doubling of megapixels dois not result in a loss of a stop of "sensor noise performance". In fact, if you took two hypothetical sensors, one at 6 MP and one at 12, with zero space between photo sites and otherwise identical sensor tech, and took shots of the same scene at identical settings with both, you would find that the amount of noise of the 12MP image when downsampled to 6 MP was identical to that of the 6 MP image. And before the noise was significant enough to obliterate the resolution advantage, you would obviously still have an advantage, and you'd never a disadvantage at any ISO.

A better way to put it is that gains in sensor resolution are better realized at lower ISOs.

 

[punchkin]

Originally posted by: jpeyton
I could take award winning, publication-ready professional photos with a 4-megapixel Nikon D2h, as long as it has quality glass attached to it.

That depends heavily on the publication. You'd not find many customers at least at the higher end submitting 4 MP images. You'd find zilch in some areas.