Image DPI in Photoshop, which number?

[rustigsmed]

Hi,

Does anyone know if if the pixels per square inch in photoshop make any real difference? The default is about 72 from memory but you hear of people when printing or entering comp's that they should be set at 300 or so.
By having the setting at 72 does that degrade the tiff image and should i be setting it higher? I assume it might have a difference when printing.

Thanks

Rusty

[chardie]

i too think it only relates to printing. so changing your photos from 72 to 300 will only effect your printing resolution not your image resolution. so i would expect no loss of picture quality. probably not articulating myself very well this time of night but thats life.

[grimsay]

Yes, standard print is 300 dpi. 72 is the standard res of older monitors, bear in mind that higher res monitors are now common e.g. Retina display Macs, smartphone etc.

Changing the resolution on an image will only affect its quality if you also force it to change size in relative to the resolution. For example increasing the size of a 72dpi image will reduce its quality quite rapidly, increasing the resolution will not help.

If I print a 72dpi image to retain quality I need to print it smaller than its size at 72dpi because I need to get it as close to 300dpi as possible. (Having said that in print productions you can get away with some image being as low as 180ish dpi even for publications without the average reader noticing.

These days also a 72dpi image will appear degraded on mostnewer devices when viewed at 100% (full size).

Ultimately it depends on the images usage. Default rule in my world (graphic/web design) the larger the resolution and size (dimensions) of the original the better as this will be more flexible later.

[rustigsmed]

thanks very much for the input guys,
so only change the DPI if i'm looking to print the image somewhere?

[grimsay]

Yes and no... I'd keep originals of the images as hi-res as possible (as file size/storage allows).

When printing make sure the dimensions you wish to print don't cause the resolution to fall to a point where image quality degrades i.e. 300dpi

Generally screen/online usage is the only time I change the res of an image (always using a duplicate) bringing it down to x-width pixels X x-height pixels at 72dpi. The aim being to reduce the files size for upload and delivery.

Of course I'm only speaking from a graphic design perspective. I'm a complete astronomy newbie and have zero astrophotography experience so someone with more experience there may be able to advise you better? The principals would be the same however I imagine.