Not sure where everyone was when this originally posted, but I just happen to notice it and there is too much misinformation throughout the threads--now let's hope I won't screw it up....
First, I'm not going to get in to the whole 72 "dpi" myth thing--don't have time, headed to Chicago shortly...
But let's clarify some things from what I've seen so far---
Macs were based on the 72PPI (not DPI) and Windows was based on 96 PPI originally--BTW, all desktop computers are "PC's" or "personal computers."
The reason we have 72 PPI/DPI is because of Picas and Points. In fact, if you open Photoshop and go to Preferences>>>Units & Rulers you will see Points/Pica sizes then under there "Postscript (72 Points/inch) Macs were adopted by graphic and creative professionals early on because you could practically measure the screen and compare it to your printed output--it was all about fonts back then more than images.
Now if there was ever a push about "72" it was because Photoshop started out as a "Mac/Apple only Program" until they bought out Aldus PhotoStyler and of course technology changes every Monday when the Board of Directors meet so 72 was adopted as the standard because it works with graphic, layouts, design, typesetters, photographers, art directors, copy editors, etc., but more important it worked with FONTS, postscript, etc. Even today newspapers, magazines, books, etc., are based on picas/points and "column inches" when it comes to design and printing--oh, and they use "line-screens" to print (Newspapers 65 or 85 and magazines 133, 150 or 175) Rule of thumb for photographers shooting for publication, "two times the line screen, plus/minus 20-percent" and shoot full-frame because an image is used in proportion (percentages) and column inches, not 5 x7's or 8 x10's.
Editors will kill you if you leave room for cropping in 35mm, digital or film for that matter. A sure sign of an "amatuer" publication shooter is one that leaves room in the frame of capture so they can print 8 x 10's to fit a frame.
DPI is irrelevant when it comes to monitors, cameras, scanners, etc., unless you have a
target DPI you are shooting for
in a printable outcome. You will still capture in PPI but it's only relavent if you have to output a certain file size.
The statement "DPI=Quality" is wrong unless you're a printer, and even then it doesn't mean anything if you have to interpolate to get to the higher DPI. Remember, Photoshop doesn't work in DPI, it's native is PPI.
Here's an example, two images, and you can download them and open in Photoshop to verify. The images look identical, if you download them and print them, you'll find out that one is much smaller in size when it comes to printing. In fact the first image is saved at 72PPI and the second at 300PPI. The amount of pixels in each image is the same!
So does an image have to be saved on 72 PPI for the web, the short answer is no. However, it's done that way because of postscript, fonts, picas, points, etc., from the old Mac days of 72PPI monitors. Creatives that worked on Windows back then had a monitor of 96PPI and had to calculate with the "133-percentage" rule. If you liked math then Windows (actually DOS back then) was for you.
Now back to some of the mis-statements. The two images below, from way back when screen captures, shows how if you check "resample" in Photoshop you will get not only a larger image on screen and on paper, but also a larger file size--look at the numbers, they are all relative to another in this type of example. If you do not check "resample" then you can change the PPI all day long and save it for the web and the image "screen" size will remain the same and it's only relative to the user's monitor settings (resolution).
The reason we see "pixelization" on a print with an image saved at 72 PPI is because there are 72 pixels in that one-inch and the human eye can see 72 little bricks in one inch--it's very difficult to see 300 little bricks fit into one inch. Monitors don't care what the print size is, they only care about the total pixels in length by the total in width, that's what it will display.
Now let's get the terminology straight. STOP talking DPI unless you're talking about a printer's output. BTW, the 300 DPI "myth" comes from the older laser printers. Why not print at 305 DPI? I don't want to get into that, but just be aware that 300 came from somewhere and it originated from laser printer technology.
Cameras capture in PPI, pixels per inch, not dots! Same with monitors.
Scanners scan LPI, lines per inch.
Now that's my two centavos worth...wishing everyone the best, rg sends!