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Old May 22, 2007, 9:07 AM   #1
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Guys, I've had the Alpha 100 for several weeks now and I think it is a tremendous camera. I trully haven't used the full power of it and I'm really still just learning. Something puzzled me and I'd be grateful if anyone could either tell me I'm being daft or there is a setting I missed.

I have the image size set to L and the quality set to Fine and I'm very pleased with the shots I've taken. I pulled up one of the images and checked the properties. I noticed that against Horizontal and Vertical Resolution it said 72 DPI. That seemed very low to me. I then checked a similar photo I had taken with a Canon G2 (4 megapix) and it's properties showed 180 DPI.

Is there a setting I need to change on the camera? I have the Digital Field Guide book and there doesn't seem to be anything in it talking about resolution.Sorry if this is a dumb question and I'm just missing something very obvious.



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Old May 22, 2007, 10:20 AM   #2
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DPI is Dots Per Inch. This is the default resolution that the camera thinks the image will be displayed and printed at.

The camera has absolutely no idea how you will display and print your photos. The value of 72 DPI or 180 DPI is entirely arbitrary. The default resolution that PCs use to display images is 96 DPI, though it can be set to 120 DPI, or anything you want. The default resolution that Macintoshes use is 72 DPI, though it can also be set to anything. 180 DPI is the resolution that was used by very early ink-jet printers.

Again, the camera doesn't know whether you'll be displaying the photos on a Mac or a PC, or whether you'll be printing the photos on an old ink-jet at 180 DPI, a laser at 600 DPI, or a modern Ink-jet at 4800 DPI.

The number you see is meaningless, and even if you wanted to change it in the camera, you couldn't.
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Old May 22, 2007, 3:40 PM   #3
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Thanks.I just thought it was a bit weird. I first noticed it in Photoshop actually. Normally when i was editing photos form DSLRs that other people had sent me (I was using them in a book and the publisher needed 300 DPI images), I would cut an area from the original image and open an new blank image to paste into. Pshop would automatically set the resolution at 300 DPI (the image resolution of the original image). WhenI did the same with anything the Alpha produced the image resolution would be 72 DPI. I thought this was crazy until I checked the properties of the origional image and found it to be 72 DPI.

Now when I cut anything from an Alpha image I have to manually force pshop to make it 300 DPI. I must admit to still being a bit confused as to who some cameras set the DPI to 180 or 300 yet the Sony goes for something like 72. I guess there is something in the firmware which dictates this.

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Old May 22, 2007, 4:05 PM   #4
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Flying Doctor,

Please keep in mind that the vast majority of computer screens out there including pre-LCDs display at 72-Pixels per inch (Not dots per inch). It would seem to make sense from a manufacturers point of view to default to 72-pixels per inch. Again catering to the lowest common denominator.

The technology of the screen and its corresponding video driver software dictates what you see. If your video screen and its drivers can handle 180, 230, or 300 pixels per inchscreen resolutionit will figure it out.

The PShop DPI refers to print quality on paper. 300 dots per inch is generally accepted as a good compromise for printing good quality color images on paper. Yes, there are printers out there that claim 4800DPI but realistically unless you are very fastiduous 300 DPI works quite well. The untrained human eye looking at a print at 300 DPI thinks it's a chemically processed image.

Don't confuse what PShop does with what appears on your screen. You can have 72 pixels per inch on your screen and 4800DPI on paper.

Please see: http://en.wikipedia.org/wiki/Dots_per_inchfor a reasonably good explanation of the whole thing. It is unfortunate that screen resolution and print esolution use the same terms when they are actually different technologies.


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