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Old Jun 7, 2003, 1:16 PM   #1
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Default OK, still confused re resolution

Please, someone try and help me figure this out.

Have Canon S230 3.2 MP camera, in its best shooting mode, takes 2048 by 1536 pix at a screen resolution of 180. Prints very nice pix at 8 X 10 in my Canon s820 printer.

Now, if I get a 5 MP camera, I assume that I will get a resolution higher than 180, won't I? And, if I do, does that mean that if I print at a higher resolution, but still at 8 X 10, does that mean that my image will be "better"?

Can someone help me with my confusion?

THANX!
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Old Jun 7, 2003, 3:01 PM   #2
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Eventually with dpi you reach a point where a. the printer can't go higher or b. the pic is already so good, the added dpi won't make much of a difference. The extra mp will mainly only allow you to crop more or print bigger pictures since 3 mp is basically the standard for good 8x10s.
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Old Jun 7, 2003, 5:22 PM   #3
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I tend to think in terms of what the best photo printers are doing at the moment, if you get prints done on-line or at a store. At the moment it's 300dpi and these prints are the ones many people are now getting from film negs (which are scanned).

So if you want to aim for indistinguishable from 'film quality' resolution, 6-7Mpix would really be needed for a 10X8 print. However, this is not the whole of the story, compression artefacts (which you don't get with film) could blow away the potential quality of higher resolution from pixels, so you'd need to shoot fine, TIFF(uncompresed) or RAW. Higher resolution allows more artefacts to be seen, whereas lower resolution 'blurrs and smoothes the edges'. I.e the crispest sharpest pics could be spoilt by equally sharp and visible compression and camera sharpening processes.

But pixels,resolution and sharpness isn't everything. Most printers will interpolate and make more dots when printing by averaging 2 or 3 pixels. The figure of 6-7Mpix is theoretical for best resolution based on the captured image, without interpolation and therefore the most truthful in quality terms. You could make a comparison with your inkjet, by having a 10X8 printed by a shop (at 300dpi).
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Old Jun 8, 2003, 5:49 PM   #4
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If I were you I'd forget about the 'screen resolution' specification. All that matters is the size of the image in pixels, e.g. 2048x1536. If you edit the dpi in a program like Photoshop, the image itself DOES NOT change - it's just a hint to tell the application how big to print the image if you print at 100%. Since you hardly ever print at exactly this size, (180 dpi = 11.4x8.5) the value is irrelevant.
Note that if you print at 10x8 you will lose some of the image, since it is a different shape to the image. If you get a camera that is exactly 5MP you will get a 26% improvement in ppi (pixels per inch). Basically that means that it will print an image 12.6 inches across at the same resolution as one at 10 inches across with your current camera. IMHO the quality of the camera itslef will have a much greater effect...
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Old Jun 8, 2003, 8:04 PM   #5
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Thanks to all for your help!

Just a followup.

Re my printing-I do it through PS 7. Of course, I often crop, so I never print at exactly 8 by 10. What I often do is make the cropped image larger, while keeping the same aspect ratio. (And I typically resample the image)

I assume(d) that this reduces the resolution, but usually the prints come out fine.

Of course, as you may know, in PS 7 you can pretty much do everything-but I always make sure that my aspect ratio remains the same.

One further question: Are you telling me that the PS stated resolution of 180 is basically meaningless, and I shouldn't pay any attention to it?

ThanX!

MMPPINES
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Old Jun 8, 2003, 8:39 PM   #6
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Quote:
Originally Posted by mmppines
... One further question: Are you telling me that the PS stated resolution of 180 is basically meaningless, and I shouldn't pay any attention to it? ...
That is right - dpi is meaningless untill you print. And at that point, you simply resize the height/width with the "Constrain Proportions" checked and the "Resample Image" unchecked. Then look at the Resolution to make sure it is larger than something like 200, preferably 300 pixels/inch.

If you are preparing the image for the web, you will want to make the image a size in pixels (typically something like 400x600), and the dpi remains meaningless.
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Old Jun 8, 2003, 10:13 PM   #7
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However, since the image from my camera is rec'd at a resolution of 180, I would have to reduce the print size severely to get a resolution of 300.

Am I correct?
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Old Jun 8, 2003, 11:32 PM   #8
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Default Re: OK, still confused re resolution

Quote:
Originally Posted by mmppines
... takes 2048 by 1536 pix at a screen resolution of 180. Prints very nice pix at 8 X 10 in my Canon s820 printer. ...
That works out to be 8.5333x11.37777". To get an 8x10" you need to crop 128 pixels from the long edge to get the aspect ratio right. Then you need to change the dpi to 192. You would do exactly the same thing if you started with any other value of the dpi. Since you get exactly the same result no matter what the camera says the dpi is, that value has no meaning.
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Old Jun 9, 2003, 12:19 PM   #9
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When you're taking a photograph, dpi is totally irrelevant. The DPI of a photo is just a number that is stored along with the photo (like the date). It's just a number that tells a file how big to print out. Your photo could be 1dpi or 1,000,000 dpi and it wouldn't make any difference to the image. The dpi of a file is totally irrelevant, and can be easily changed at any time.

When you're thinking about printing photos, all that really matters about the resolution is the number of pixels. And this is when the literal meaning of dpi (dots per inch) comes into things.

If you want at least a certain number of dots per inch when you print a photo, then you'll need to multiply that DPI by the width of the photo in inches, which will tell you the number of pixels you'll need for the photo.

Say, for example, if I wanted to make sure my photos were at least 200dpi, and I knew I would never be printing larger than 10x8, then 200 dots x 10 inches = 2000. So, in that case I would need a camera capable of taking photos at least 2000 pixels across (ie 3 megapixels).

But other than planning how many megapixels you may need, you'll probably never need to think about dpi. And definitely not the dpi value that your camera assigns to your photos.

You mention changing aspect ratio. You shouldn't need to worry about that. If you're having prints made, the printers will take care of the cropping and they don't expect you to do it for them. If you want to crop photos for printing then work on a copy, or you'll lose part of your photo forever.
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Old Jun 9, 2003, 5:38 PM   #10
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Quote:
Originally Posted by Grand Dizzy
... You mention changing aspect ratio. You shouldn't need to worry about that. If you're having prints made, the printers will take care of the cropping and they don't expect you to do it for them.
I'd much rather pick where the cropping is done instead of leaving it to someone at Wal*Mart. If you are going to print it yourself, you are still likely to want to crop to some specific size and then you have to do it yourself.

Quote:
Originally Posted by Grand Dizzy
If you want to crop photos for printing then work on a copy, or you'll lose part of your photo forever.
Always save an unaltered copy of the original as your "digital negative". Don't mess with it in any way.
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