Check resolution and clarity for sizing?

Question

Hello - I have an issue where I print an image to a larger size, say 16x24 and the image in grainy.  How do I check in LR3 what the image will look like at the enlarges size?  I know there is a way!

Answer 1

You can't use your monitor to preview the printed output graininess of a photo because the Points Per Inch of a monitor is much lower then that of a printed output; Instead a bit of math will give you an indication of the graininess of a photo.
Divide the pixel width and height of the photo by the corresponding width and height of the intended printed output; take the smallest of these results and this will give you the Points Per Inch or PPI of the photo. For example, let's suppose that you have a 3000 pixel x 4000 pixel photo (approximately 12 Mega Pixel) and you want to output at 16 inches x 24 inches, then you would divide 3000/16=187.5 and 4000/24=166.66 so you maximum resolution given these numbers would be 166 PPI.
Typically good quality is achieved between 240 and 300 PPI but this also depends on the intended viewing distance; the further the viewing distance the lower the tolerance on PPI and the closer the viewing distance the higher the PPI should be; magazines are printed at much more then 300PPI while posters on a building may be printed at less then 100PPI.
You can tell Lightroom to enlarge a JPG output to a certain size while mainaining a specified PPI at export time or you can specify the PPI of your given print layout in the print module. If this doesn't give you satisfactory results, you may need software such as "Genuine Fractals 6" to enlarge your photo with less graininess.
Hope this helps.