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Pixel count and Downsizing
If a photo is never looked at, printed, viewed on screen, etc. at larger than 8X11 or 1280X1024 on screen, then all the high pixel-count photos are good for what? It seems the viewing software has to throw away most of the pixels, thus more processing. I would think that the highest quality results would come from the original resolution being exactly the same as the viewing resolution. Am I all wet here?.

A Puzzled Pixeler........

Comments (10)

Srfdude wrote:.

If a photo is never looked at, printed, viewed on screen, etc. atlarger than 8X11 or 1280X1024 on screen, then all the highpixel-count photos are good for what? It seems the viewing softwarehas to throw away most of the pixels, thus more processing. I wouldthink that the highest quality results would come from the originalresolution being exactly the same as the viewing resolution. Am Iall wet here?.

No, you are exactly correct. Viewing on a computer screen requires no more than about 1MP of information, and if you are viewing on-screen, it makes sense to use the same number of pixels as the screen has to avoid interpolation which can cause artefacts to appear..

Best wishesMike..

Comment #1

Thanks Mike. As far as printing, if you have say Costco print your pics in 5X7, how many pixels are printed? How about a home printer? I just looked at the setup in my HP but it didn't specify. Surely it won't print 6 or more MP? I guess what I'm asking is , who is able to use all the pixels in the ever increasing pixel race going on? Seems the noise levels just go up.Mike..

Comment #2

If you print at a usual 300 dpi, you need 8.4 mp to print an 8 1/2 x 11 without any cropping. Even minimal cropping will require a 10-12 mp image. Professional printing is often done at considerably high resolution. Aside from a give away snap shot I don't print anything less than 8x10. When I retire, I may try 4x5 large format photography. That is the minimum quality required by Arizona Highways and for many other photo applications...

Comment #3

Continuing on the same idea:.

Sometimes you know you won't be using your pictures for anything else than on screen viewing and small prints, so you don't NEED all the MP and select a lower resolution, say 2MP instead of 8MP....

How does your camera actually make the picture? Does it simply ignore 3/4 of the available pixels? Or is something more complicated going on?.

I could e.g. imagine that the camera combines the information of 4 pixels into 1, and that therefore the result has better colors and less noise.....

Basically: why and when is it better to select a lower resolution in-camera?..

Comment #4

As jrkilny pointed out, the commonly-accepted standard for high resolution printing is 300 pixels per inch. The human eye cannot resolve detail finer than this, even quite close up. So your 7 x 5 print needs 2100 x 1500 = 3.2 MP. If you are not going to print larger than this, e.g. for a typical family album, then you are right that the current number of MP is unneccessary (although it will give you scope to crop if you want)..

For larger pictures, 300 pixels per inch is not always necessarily because they are viewed from further away. A wall-mounted poster is not likely to be viewed from 30 cm away, so lower resolution is fine, and there are many users on this form who have said that they can make very good 30 x 20 prints from a 6MP camera. That comes to a linear resolution of only 100 pixels per inch, but at a viewing distance of 1 - 2 meters that's probably enough to look acceptably sharp..

Ultimately it depends on your requirements. I find 6MP plenty and very rarely print pictures bigger than A4 sized. If you want to make much bigger, very high quality images of publication / exhibition quality then the standards required are likely to be much higher and large-format film cameras may be the instruments of choice..

For most users though your sentiments are quite correct... more and more MP crammed on to a sensor gives invisible increases in resolution at the likely cost of more image noise. My sister has a Canon EOS400D (Rebel XTi) which she is very pleased with, but never prints anything bigger than 6 x 4 inches, which gives a linear resolution of over 600 pixels per inch.... the printer will print it but such resolution is pointless until the human eye evolves differently!.

Best wishesMike..

Comment #5

The more megapixels, the lower the potential image quality. However, some improved image processing accompanies newer cameras of higher megapixels, so the end result can be the same..

Mike703 wrote:.

As jrkilny pointed out, the commonly-accepted standard for highresolution printing is 300 pixels per inch. The human eye cannotresolve detail finer than this, even quite close up..

Who told you that?..

Comment #6

Mike703 wrote:.

As jrkilny pointed out, the commonly-accepted standard for highresolution printing is 300 pixels per inch. The human eye cannotresolve detail finer than this, even quite close up..

Who told you that?.

I don't know, to be honest... but the figure of 300 pixels per inch as the maximum necessary for high-res printing is commonly used (see jrkilny's post earlier) and I've seen it used many times..

This is from http://en.wikipedia.org/wiki/Eye.

'For a human eye with excellent acuity, the maximum thoeretical resolution would be 50 CPD (1.2 minute of arc per line pair, or a 0.35 mm line pair, at 1 m). However, the eye can only resolve a contrast of 5%. Taking this into account, the eye can resolve a maximum resolution of 37 CPD, or 1.6 minute of arc per line pair (0.47 mm line pair, at 1 m).'.

So at a viewing distance of 1 metre a human eye 'with excellent acuity' can resolve one dark/light line-pair every 0.47mm. This makes (25.4 / 0.47) line pairs per inch, which is 54 line pairs per inch, equating to a linear resolution of 108 pixels per inch. That is about what you would get from a 6 MP picture printed at 30 x 20 inches (100 pixels per inch)..

This will scale linearly with distance, so at half the distance you can resolve twice as many pixels per inch. So at a viewing distance of one third of a meter, the eye could resolve 108 x 3 = 324 pixels per inch. On this basis, a figure of 300 pixels per inch as a standard for high-res printing of photos seems very sensible: most people don't tend to look at photos from a distance of less than a foot..

Best wishesMike..

Comment #7

Pieter Missiaen wrote:.

How does your camera actually make the picture? Does it simply ignore3/4 of the available pixels? Or is something more complicated goingon?.

I've often wondered the same thing. The only manufacturer I've noticed addressing the issue is Olympus (though I might have just missed others). Without going into detail, Olympus simply says things like, "Unlike traditional digital camera designs which throw away pixel information to create smaller file sizes, TruePic uses all the pixel information to create a better and truer photographic image at the lower pixel resolutions." The fact that I haven't seen Canon, for example, make the same claim for their Digic processor doesn't mean they don't do something similar, but they don't seem to be promoting it if they do. I appreciate that Olympus offers a wide range of lower resolution settings, and this was one of the reasons I bought an E-300...

Comment #8

Mike, you neglected to quote part of the wikipedia article that estimated the human eye has the equivalent of 81 mpix. That sort of comparison might not make a lot of sense seen we see clearly in only a limited field of view. Then again we move our heads and eyes constantly scanning our environment. We seem to accept what we are used to - relatively small and low resolution prints...

Comment #9

I'm using a D80 at around 5 millions pixels instead of the maximum 10 or so millions pixels. What happens to the unused pixels on the CCD ? Or are they "teamed" 2 by 2 ? I know I'm loosing in finesse but do I gain anything beside more pictures on my SD card ? .

Alain1754 North 6248 West. Ocean at 26 Celcius (78 Fahrenheit) 365 days a year.....

Comment #10

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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