If you care about image quality, your images should be 355 ppi (pixels per inch).
Beware of screen resolution (or the number of pixels required to display an image satisfactorily to a computer monitor...usually around 72 ppi ).
Print resolution (or the number of pixels required to display an image satisfactorily with ink on paper) is much higher - most printers ask for a resolution of 300 ppi.
At Modern Postcard we have a higher line screen than the average printer and so we ask that an optimal image resolution be set at 355 ppi.
Take a look at the following examples:
The image above will print great at 355 ppi...
...but will print badly any lower than 300 ppi!
Q: OK, I understand that low resolution is bad.
Can I just change my 100 ppi image in Photoshop to 355 ppi by changing the number?
A: Not exactly.
When you "change the number" from a low resolution to 355 ppi, you are not really addressing the underlying problem.
Doing this is called interpolation.
Interpolation means that you are asking the computer to calculate the pixels that are not there.
Computers cannot add new data to sharpen the image, it can only add pixels that "fill the gaps."
What you end up with is a tiff that is at 355 ppi, but very, very blurry.
Q: OK. So how do I fix low resolution?
A: You need to re-scan your photograph, slide, or transparency at 355 ppi at the final size you want it printed.
Note: When placing images into layout programs like QuarkXPress, PageMaker, or InDesign, be sure not to scale the image up or down much.
A 355 ppi image, for example, scaled up 200% will have a final resolution of 177 ppi! Low Resolution!
Also be sure not to overcompensate by making your image resolution too high.
It is overkill to have images at 600 ppi, for instance.
It not only makes file sizes significantly larger, it also may create problems with final printing.
Again, 355 ppi is the optimal resolution for raster images.