pandoany115 Loc: Los Altos, CA

Are, say, 300 ppi and 300 dpi of same quality of phto prints?

CaptainC Loc: Colorado, south of Denver

Those two terms have no relation to one another.

PPI is how many pixels of the image are in one inch.

DPI is a measure of how many DOTS a printer has to lay down in one inch. A printer has to spit out multiple "dots" to mix colors to render the correct color for the print.

YOU control the PPI dimension in the Image Size dialog. If your image is 2000x3000 pixels and you set the PPI to 300PPI, you image will print 6.6x10 inches. HOWEVER, if your printer is printing at 1440DPI, it will lay out as many as1440 dots in every one of those 10 inches. If your image is 240PPI, your image will now be 12.5 inches wide but the printer will still lay down 1440 dots in every inch of the 12 inches.

Printers have to mix the "dots" to make the colors. Unless the color in your images is the exact same as the (for example) magenta in your printer ink, the printer driver has to figure out what colors to mix to give you the shade of magenta color needed.

pandoany115 Loc: Los Altos, CA

Thanks, CaptainC. I had read an article, where ppi and dpi were mixed and I was confused.

mborn Loc: Massachusetts

excellent answer

GoofyNewfie Loc: Kansas City

Agreed. The best I've seen so far.
Heaven knows there have been many opportunities.
Should be in the FAQ, should anyone wander over there to read it.

Pentony Loc: Earth Traveller

:thumbup: :thumbup: :thumbup: :thumbup: :thumbup:

marcomarks Loc: Ft. Myers, FL

While I agree with CaptainC, I resize my files to be 300ppi (a desired 8 x 10 inch print is done with a 2400ppi X 3000ppi file) and I always get excellent results on any printer that is printing at 300dpi or less. Ppi and dpi are very loosely related but as you can see by CC's reply, not precisely at all. Pixels are electronic spots on a screen and dots are ink spots on paper, two different but somewhat related things. The printer will throw away excess pixel resolution it can't convert for print.

I always relate 300ppi to whatever inch-size print I want that is actually going to be printed in dpi by doing a quick math in my head as to what ppi I will use to create the file. It always works.

It's a gray area such as looking at a file's MB (megabyte) size doesn't really tell you how many pixels wide and tall that it is, but it can give you a general idea whether the file will or won't likely print well. Somebody may ask if their 57KB (kilobyte) JPG file they got from a relative as an attachment on an email will print as an 8X10 and there's not a snowball's chance in hell that it will. I know automatically that it will require at least a 1.3MB size JPG file to hold all the pixels that are required for a nice clean 8X10. MB file size, ppi, and dpi are not actually related but MB file size can give you a relative idea of what's inside.

A RAW file may be 30MB in size, the TIFF version of the same file may be 10MB in size, and a JPG version with mild compression may be 1-3MB in size. That doesn't say much about what's inside the file but you can know if the size of the file is within "the ball park" of what the user wants to do with it.

Hopesfate Loc: NC

Thanks Captain C for clarifying this. I have been a bit confused about it as well. So much goes into the actual print
process that it is very confusing for us that are not professionals.

GC likes NIKON Loc: East Greenwich, Rhode Island

Cliff, I am a little confused here....Please teach me something (gently please). What I don't get is why reducing the dpi from 300 to 240 makes your image size (dimensions in inches ??) larger. My mind thinks smaller DPI means smaller image size......... ????

CaptainC Loc: Colorado, south of Denver

Understandably confusing. Remember we are taking pixels per inch - not the size of the pixels. If you have fewer per inch, the same number of pixels then cover a greater distance.

If you have 3000 pixels on the long side and have 300 PPI (NOT DPI), then that covers 10 inches. If you change the pitch to 150 pixels in one inch (PPI), you now cover 20 inches.

Does that clear it up?

GC likes NIKON Loc: East Greenwich, Rhode Island

But at less quality ???

CaptainC Loc: Colorado, south of Denver

Like many things, it depends. For larger prints - say 11x14 and up - you can get by with increasingly smaller PPI numbers. When I print 11x14 16x20, 20x30 etc, I always use 240 PPI and they are perfect. For canvas prints you can easily use 150PPI and get great results as the medium itself is so coarse.

Much depends on the viewing distance and large prints up on a wall can get by with 240 or even 180 PPI and look fantastic.

The extreme, of course, is that billboard at 300 yards - look at that thing close and the pixels can be the size of golf balls.

Hopesfate Loc: NC

Thanks for clearing up some of this confusion for me also.
I've always printed 300 thinking that is best.

CaptainC Loc: Colorado, south of Denver

I should ad that my lab - ACI - requests the images be sent at 250PPI, sRGB. The results are superb.