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Old Apr 25, 2003, 11:08 AM   #1
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Default Query over actual image resolution of different makes

Hi guys,

In my quest for the best dig camera for me (I currently still own the Canon S10 would you believe! ) I have come across something I have not seen mentioned anywhere before in the realms of Digital Photography.

I am talking of the resolution (not dimensions) of the image when you drag it into Photoshop or other software. From what I have seen, this seems to depend on the make of the camera and not the model.

For example, any image regardless of its dimensions taken from my humble but good Canon S10 and dragged into Photoshop, comes in at 180 pixels per inch. Likewise for other Canons like G3 and S50. Nikons seem to be 300 pixels per inch. Alll the rest seem to be only 72 pixels per inch.

Am I missing something here or is it that images having the higher resolution pixels per inch like 180 offer advantages over those that are only 72?

This would be interesting to hear more about before I make my definitive camera choice out of Sony F717, Canon G3 etc.

Best regards

John Leigh
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Old Apr 25, 2003, 11:39 AM   #2
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The confusion is the 180dpi is closer to a resolution for printing, while 72dpi is for viewing on a monitor...it just means you have to convert one to another, either way depending on what you're doing (some newer cameras have both printer and monitor resolutions, and adjust the DPI accordningly).

For instance, my 2mp camera takes a picture at 1600x1200 @ 72dpi which is 22.2"x16.6". If I convert that to 180dpi it becomes 8.9"x6.7" but it's still viewed at 1600x1200. Having the 180dpi already in camera it would save me a step in converting for printing.

(actually for 2mp, to get 8x10 you have to go down to 150dpi)
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Old Apr 25, 2003, 12:39 PM   #3
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For some reason this is very difficult to explain in detail. Measurements in inches or centimeters, applied to the digital images you get from your camera, are complete red herrings and serve no other purpose than to cause confusion.

Your camera produces an image X PIXELS wide by Y PIXELS high. Not inches, not centimeters, not dots.

What you do with those pixels is between you and your software. Generally, for screen displays you need fewer pixels than your picture provides, so your display software discards some. Some software makes a good job of this, other software does it less well. People who complain of "jaggies" when they view their pictures on screen have often got the latter.

For printing it's more or less true that you can't have too many pixels. The more pixels you have the bigger you can print without loss of quality. Again, if you do your own printing your software will look after this for you, producing the best print it knows how from your original image. Some printing software, like Qimage, does this superbly well. Take any picture, tell your software how big you want the print, and the software will make the most it can of the pixels you give it to work with.

If you don't do your own printing, for "software" read "photo lab".

The only thing you really need to watch out for is the proportions of the picture. Standard screen sizes are in the proportion 4:3 (hence screen resolutions expressed as 640x480, 800x600, 1024x768 etc.) Printing proportions vary: 3:2 (for 6x4 prints) or 7:5 or 5:4 (for 10x8s). It follows that what fits perfectly on your screen WON'T print perfectly as a 6x4 because the proportions are different. What prints as a 6x4 won't make a perfect 10x8. What comes directly out of your camera may not exactly fit ANY of these sets of proportions.

If you want a screen display that fills the screen corner to corner, you will need to crop your pictures to 4:3. If you print your own pictures, you can either crop to whatever proportions you wish to print at, or use whatever proportions best suit that particular image and end up printing every picture at a different non-standard size. I see no disadvantage to that - it makes for an interesting photo album! A photo lab will automatically crop your image as needed to fit the paper it uses - if you want to control what the lab chops off rather than leaving it to their machine, crop your images as you want them printed before taking the files for printing.

When adjusting the proportions of your images, remember - you are always working in PIXELS. You can start with one image 1200x800 pixels and another 1443x962 and if the quality of the image is otherwise good, both will produce a perfect 6x4. Let the lab or your own software worry about converting pixels to inches, you just look after the proportions.

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Old Apr 25, 2003, 2:18 PM   #4
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Let the lab or your own software worry about converting pixels to inches, you just look after the proportions.

So if I'm understanding you. I take my pic at 1600x1200. When I open it in VuePrint it tells me it's 22x16 inches at 72dpi. I upload it to walmart.com for printing. They'll take care of sizing it and the correct dpi for my 4x6 print. Is that right?

Thanks, Brad
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Old Apr 25, 2003, 4:03 PM   #5
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That's right. But at 1600x1200 the proportions are 4:3 - just right for screen display, but wrong for a 6x4 print. For 6x4s the lab will have to crop a strip off each of the long edges to give an effective size of about 1600x1066 pixels, which is 3:2.

If you leave it to the lab, sooner or later you'll lose the top of someone's head - or their feet. If you want to control what gets cropped, do it yourself before you send the files to the lab. As you have Photoshop, you should have no trouble cropping to the size needed.

VuePrint's 22x16 inches at 72 dpi is misleading. 1 pixel in an image or on a screen does not equate to 1 dot on a printer.

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