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01-19-2009, 07:00 AM   #1
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Question About Resolution

Hey All,
Lets say I'm going to take a picture that will be turned into a poster of 20 X 30, will you see much of a difference if my k200d settings are 100 ISO and 6MP mode or 400 ISO and 10MP mode. I'm thinking ut would be about the same quality. This is mostly a question how resolution and ISO settings work together.

Thanks
Barry

01-19-2009, 07:36 AM   #2
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Resolution and ISO are separate settings. One doesn't relate to the other.
01-19-2009, 08:15 AM   #3
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QuoteOriginally posted by Wheatfield Quote
Resolution and ISO are separate settings. One doesn't relate to the other.
Well, they do relate indirectly - a higher ISO image will lose detail due to noise, noise reduction, or a combination of the two, so effectively, this loss of detail is basically a loss of resolution.

I think what the OP is asking is if he'll see any difference in quality of the large printed image - 6MP at ISO 100 or 10MP at ISO 400.

If you expose correctly, you won't see much noise at ISO 400, and that will probably give you more detail than 6MP at ISO 100.

Why not shoot 10M at ISO 200 and hold it really steady or use a tripod?
01-19-2009, 08:19 AM   #4
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QuoteOriginally posted by shutterpuppy Quote
Hey All,
Lets say I'm going to take a picture that will be turned into a poster of 20 X 30, will you see much of a difference if my k200d settings are 100 ISO and 6MP mode or 400 ISO and 10MP mode. I'm thinking ut would be about the same quality. This is mostly a question how resolution and ISO settings work together.
If you stand back far enough the photo with the lowest ISO will look best because it'll have less total noise (longer exposure). Of course if you stand back far enough, everything looks the same; all of these variables depend on how far back you stand from the print.

Regarding how the 6mp & 10mp images will look, again it'll depend on how close you stand. The 10mp image has inherently better resolution, about 20% better, but it'll also have more noise per pixel because of the shorter exposure (there'll be 1/4 as much light distributed over 10/6 as many pixels; each pixel will have only 6/40 as much light as the 100ISO, 6mp photo - about a 2.6x worse signal to noise ratio for each pixel..)

.... I can't go much farther with this discussion because too much depends on how far away from the print the observer will be and how much one values spacial resolution over noise.

10mp will print out at 129 pixels per inch & 6mp will be 100pixels per inch so both will look pixelated & coarse up close. You could artificially increase the pixel count with a good interpolation program (up-sizing) to say 200ppi, then they'd both look pretty smooth up close, but I expect the increased noise on the high ISO photo would be objectionable.

Can you tell us more about how you value resolution compared to noise?

01-19-2009, 10:58 AM   #5
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If you could shoot the 6mp camera at ISO 100, why not just shoot the 10mp camera at ISO 100 as well and have a result superior to either of the options you suggested?
01-19-2009, 11:09 AM   #6
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QuoteOriginally posted by shutterpuppy Quote
Lets say I'm going to take a picture that will be turned into a poster of 20 X 30, will you see much of a difference if my k200d settings are 100 ISO and 6MP mode or 400 ISO and 10MP mode.
I assume you are thinking that selecting a lower resolution setting gives you larger pixels and hence less noise? There's practically no way it's going to work that way - the physical pixel size doesn't change. All the 6MP setting does is shoot at 10MP and then downsize. If you're planning to then upsize, you've basically just thrown away detail you really could have used. There is no possible advantage to *ever* choosing a lower resolution (unless you are concerned about file size, which you shouldn't be if you plan to print big).

So the answer is, best quality will be 10MP and ISO 100.

QuoteQuote:
I'm thinking ut would be about the same quality. This is mostly a question how resolution and ISO settings work together.
They don't. Raising ISO lowers quality regardless of resolution, and lowering resolution lowers quality regardless of ISO.
01-19-2009, 11:45 AM   #7
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At 20*30 under 800 ISo you need every pixel you can get. Even a 10mp image needs to be up sampled at that size.
01-21-2009, 08:39 PM   #8
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QuoteOriginally posted by Alfisti Quote
At 20*30 under 800 ISo you need every pixel you can get. Even a 10mp image needs to be up sampled at that size.
You're probably thinking back to the film days when a 25asa yielded a really fine grained shot suitable for larger prints. Now it affects noise instead of grain. I alway shoot at the highest resolution the camera allows. But the quality of the print will also depend on the output device. Some of the large format inkjets will do an amazing job at that size where others will, well, basically suck. I've run some customer files on an HP that just floored me with the output. And saw the same file on other devices that had the opposite effect.

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