72dpi resolution default

Janice Hobbs

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Apr 14, 2003, 4:46:24 AM4/14/03

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If I scan an image into Photoshop 7 at 300 dpi for example, when the image properties are checked in Photoshop, it always says it has a resolution of 72dpi.(ok for screen but not for print I always understood!) I want to print at 300 so i change this box from 72 to 300 and save the image.
Next time I open it, it is back at 72dpi again. Surely if it has to get it up to 300 it will use interpolation which is not good?

Gary Hummell

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Apr 14, 2003, 7:23:23 AM4/14/03

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Scanners and cameras basically deliver pixels. When you specify the pixels per inch PPI, the program is simply doing the math to tell you how big the picture would be at output. You can change the PPI (resolution) as you like and as long as the Resample Image box isn't checked, no harm will come to your file. There is no interpolation when there is no resampling.
When you save a file in Photoshop, the resolution you specify should be the resolution that the file opens with.

Mac McDougald

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Apr 14, 2003, 9:44:43 AM4/14/03

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PhotoShop 7 should respect the ppi at which you scan a file into it with
TWAIN.

It definitely will save ppi tag when file is saved as Tiff,Psd,JPG.
(it won't save the tag if Save For Web is used).

Btw, be sure you have Resample OFF when changing from 72 to 300 and
you'll be using only original pixels.

If you are saving files at 300ppi, then when you reopen them, it's
showing 72ppi, then something has gone awry.

Try deleting prefs in that case.

Mac

Chris Cox

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Apr 14, 2003, 9:46:20 PM4/14/03

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Janice - also, some file formats don't have a place to put the resolution information....

Lundberg02

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Apr 15, 2003, 9:09:46 PM4/15/03

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A file that is brought into Photoshop as pixels, such as a digital camera file,will always open at 72 dpi.. If you don't resample, SAVE will save it as pixels, SAVE AS will save it at the dimension and resolution specified. Isn't this correct? I can't understand what her problem is because she didn't say what she was actually doing.

Mac McDougald

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Apr 15, 2003, 9:20:37 PM4/15/03

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No it is not correct.
Many cameras tag the TIFF or JPEG images for ppi.
My Kodak 4800, for example, tags both for 230ppi, and PhotoShop opens
them at that ppi.
PhotoShop 7 is the first version to honor those tags if they are done in
EXIF. If done in main header area, PhotoShop has always honored the tags.

Untagged images do indeed open at 72ppi, as they do in most programs by
default. Some proggies, like PaintShopPro, let you set a default ppi for
opening untagged files.

Mac

Brian Everhart

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Apr 22, 2003, 3:35:00 PM4/22/03

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Look at your Preferences-Units & Rulers tab. Your Print resolution should be set to 300 dpi and your screen res at 72 DPI. Photoshop should open TIF files at 100% at the print res from this preference.

Mac McDougald

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Apr 22, 2003, 4:10:28 PM4/22/03

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That's for NEW docs (ones you make from scratch) and take effect
depending on what preset you use from the new file dialog.

That will not override any ppi tag already embedded in existing image
header.
Or EXIF ppi from digicam file.
Or absense of either of those tags in existing image. If no tags at all,
will still use 72.

Mac