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10-05-2010, 07:18 AM   #1
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DPI Question

Caro Amigo,

Talvez possa me ajudar numa dúvida:

Na Pentax ao configura uma foto com qualidade superior 14M - 4672x3104 podemos imprimir cópias no formato A2 com qualidade.

Se você abre essa foto no Photoshop ela aparece com grande formato 136,6x91044 cm e com 72 pdi.

Como fazer para interpolar essa foto para 300 dpi ? com qualidade.

Tive uma outra câmera que os arquivos saiam com 300 dps, com a Pentax com sair as fotos com 300 dps ?

Será que pode me ajurar ?


10-07-2010, 06:14 PM   #2
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You can change the image's base resolution to 300 dpi from 72 dpi but DO NOT resample it. By changing the photos base resolution to 300 dpi, your image measurements will shrink to a size smaller than large format.

You will not be able to increase the resolution to make it sharper at a larger size. At best, you will have the clarity/resolution of the original.

If you resample the image, you will make the file size and final print larger, but it may actually make the photo look worse. Resampling will not make the photo clearer. I would only recommend changing the image's base resolution. Your image will print smaller than if it were printed at 72 dpi.

To change the base resolution of the photo:

1. In Photoshop, go to Image>Image Size. (Under the Image drop down menu)

2. At the bottom of the image size box, there are 3 items you can check. Place a check next to Constrain Proportions. Make sure that the is NO check on Resample Image. It is OK if Scale Styles is checked.

3. To the right of Resolution, remove 72 pixels/inch. Type in the new number, 300. When you do, you will see the Document Size numbers get smaller.

4. Click OK.

Your picture will now be at a 300 dpi resolution and the outer dimensions will be smaller than they were at 72 dpi.

You will not be able to increase your resolution and keep the same dimensions on the photo.

And remember, never work directly on your original photo. Always modify a copy.

I hope this helps.

10-07-2010, 06:45 PM   #3
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I wouldn't pay any attention to the number 72 dpi or whatever

Make it simple - If you image is 4672x3104 and you'd like to print in 300dpi, just some simple divisions: 4672/300=15 (approximately) and 3104/300=10 (approximately). You can print in 15 in.X10 in. format.
10-07-2010, 07:13 PM   #4
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The advice here is good. Ignore that 72 number. The reason for it goes back to the original Macintosh computers in the early 1980s.

Just for the record, DPI is a misnomer dating back to that era and earlier. Dots per inch is a scanning and printer density term. What you are actually concerned with is PPI: pixels per inch.

What final output size of a print are you aiming for? The magical 300 ppi is only useful on smaller prints that require viewers eyeballs to be so close to the image. You can output an acceptable print at A3 size with a 200 ppi resolution. Or less depending on your post processing skills and printer.


10-07-2010, 08:34 PM - 1 Like   #5
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Everybody above is exactly correct. 72 dpi is standard Web screen resolution and nothing else. At 72 dpi, a ~3K x 4K image fills a REALLY BIG screen at 100% enlargement. A fact about resolution: print it small enough, or display it far enough away, and almost anything looks good. I've shot many 811x1216 pixel images with a 1mpx digicam. Printed at 6x9cm (2.25 x 3.25 inches) on the right paper and mounted correctly, they're indistinguishable from 6x9cm MF film contact prints. Do some PP and print them at 14x20 inches and hang them right, and they're good posters.

Images on a computer screen DO NOT look like the same images on a TV screen, or printed, or displayed in any other medium. Your original image is transformed by presentation, such that the image contributes 30% and the presentation is 70%, or thereabouts. How a picture is printed makes a big difference too. Your picture in a magazine ain't like your picture when you run it off your home printer and ain't like how WalMart would render it; and those could all be mounted and matted and glassed and hung in various ways to look like quite different images.

But don't believe me. Try it. With your home printer, use different papers, different widths and colors of mattes, different frames, hung in different places with different lighting, with different size prints. You'll be amazed.
11-06-2010, 03:14 PM   #6
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Aos Amigos Cynthia, Miguel e Rio Rico obrigado pela ajuda.

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