BetterPhoto Q&A
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Dennis Creaghan		Print size Is there a rule of thumb to determine the largest quality print that can be produced vis a vis the pixel size and the dpi printed at. I read somewhere to simply divide the pixels (width & height) by 200dpi. True? Thanks in advance, Dennis To love this question, log in above March 27, 2007

Marius Liebenberg		Some printers recommend 300dpi minimum To love this comment, log in above March 27, 2007

W.		300dpi produces image quality on a par with 35mm color negative film. Goto the megapixel calculator (http://web.forret.com/tools/megapixel.php), fill in your pixel size, hit 'calculate', and you will see the max print size. Have fun! To love this comment, log in above March 28, 2007

Alan N. Marcus		Hi Dennis, I wish I could provide a formula that all will agree is good but alas there are too many variables. This is a complicated subject and the answer is a variable based on file type and printer model, prints size and viewing distance is also an important consideration. That being said, the following may be useful. Print quality vs. file size: High quality file 300 PPI or better. Good quality 150 PPI Fair quality 100 PPI Formula: Print height x PPI x Print width x PPI = Total pixels that comprise the image For an 8x10 high quality 8 x 300 x10 x 300 = 7,200 7,200 is approximate number of pixels. In this illustration the pixel is the smallest unit (picture element) that conveys intelligence. Now the color digital image requires that the pixel be fractured into three sub-pixels. R- G – B – for the three primary colors red – green – blue. Thus the pixel count is multiplied by 3 thus: 7,200 x 3 = 21,600 For 4x6: 4 x 300 x 6 x 300 x 3 = 6,480 This value is o’ so rough! There are so many pitfalls such as file type, compression method, camera sensor layout, ink-jet – dot matrix – dye sub – electro static - PPI vs. DPI ad nauseam. Alan Marcus ammarcus@eartlink.net To love this comment, log in above March 28, 2007

John P. Sandstedt		There are lots of recommendations out there. George Schaub, a BP instructor and Editor of Shutterbug in his book Digital Black and White Printing, makes recommendations in relation to file size, not resolution. For a large print [let's say 13X19] he recommends 45-50 MB files. Jon Canfield debunks the resolution myth in a recent article in Shutterbug. He suggssts that, depending on your printer, you can set the resolution for 350 ppi for prints smaller than 8X12. He, then. presents a chart and suggests that you can get good 13X19 prints using a resolution of 150 ppi. That's because, in general, you'll view the larger print from a farther distance. Interesting, he says that he allows more of a spread with some Epson printers, but stays with 300 ppi using Canons. In my experience, with two Canons [the S800 and more recently the i9900,] 300 ppi resolution is definitely the way to go. Also, I just won a statewide competition with a mere 20 MB TIF file, printed on Ilford Pearl Paper at 12X18. There really are no hard and fast rules. You need to test out your files and your printer, its ink and your paper selection. Remember NOT to confuse dpi and ppi. Your printer places ink, from one or more nozzles, onto pixels [and onto the paper.] It's very possible that more than one droplet [dot] will be played one on top of another [on the pixel] to achieve the desire color[s.] And, generally speaking, I don't think one can affect the amount of ink placed by the print head, except to say that if the printer expects 300 ppi resolution and you've set 72 ppi, you'll get a pixelated print. If you set 600 ppi, you printer just might place more ink than is necessary. The ink manufacturers love that. To love this comment, log in above March 28, 2007

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