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BlackSoxFanPerhaps i should elaborate...i was not saying that 72 dpi is the only resolution that will display and the only factor to consider. Sorry i'm running on fumes so I will try and elaborate a little more and hopefully rectify my errors.
DPI number (the scaled printing resolution stored in the image file) simply does not matter on the screen...you can have 4 images taht are all 100x100, these images below can all have different dpis (say 1, 10, 100, 1000). If you print them you are going to have 4 very different pictures. The dpi numbers act as an instruction to the printer how to print them. (how to space the pixels adn how large to print the image)
To test.... get an image and keep everything the same except the dpi, look and compare and i'll bet you'll have a hard time telling them apart on your screen. Remember that while an image might display at 100x100, depending on the dpi..it can print at 100 inches by 100inches or 1 inch by 1 inch.
There is no concept of dpi on ANY video screen. 72 dpi is a false notion. That makes it worse than if it were just useless, because it is counter-productive, both to results and to understanding how it really works. There is no concept of dpi in the video system. There are only pixels. (we're talking about 72 dpi relative to screen display not printing).
So you have 4 identical 100x100pixel images. Lets say you started with a 35mm negative scanned at 1408 dpi. Cut it by quarter: 1408/4 = 352 dpi size now (scanning 0.92 inches film width at 352 dpi would also give 324 image pixel height). The 1, 10, 100, 1000 dpi values here are very true, honest and legitimate in every way possible.
If you save all 4 of these images, and then look at them with adobe or whatever you use, and look at them carefully. You will probably notice they have different dpi's. he three images are identical size on the video screen (all are 412x324 pixels - dpi is ignored on the screen). But the four files are indeed all very different now when printed on paper, at least when you print them one at a time. Dpi is for printing on paper. The images are obviously the same size on the screen , but the images are indeed scaled to 1 dpi, 10 dpi, 100 dpi, and 1000 dpi, and the image properties definitely will show different print sizes. This dpi applies only to paper, or wherever inches might exist. DPI DOES NOT APPLY TO VIDEO SCREENS. The three images will obviously print at those inch sizes on paper (ps...we're talking about printing from a photo suite NOT YOUR WEBSITE - I will be happy to talk about this when I actually have time!) Oh yeah, and unless you have billboard printing, don't print the big boy! lol.
Pinter drivers definitely do use dpi - dpi is all important to printers because printers print on paper, and paper is dimensioned in inches. But video systems know no concept of dpi at all, nor any concept of inches either. Video systems simply show the number of pixels pixel for pixel. Any dpi value is always ignored on the screen, regardless what value it is. Dpi is simply not defined in the video system. PERIOD!
If you understand this much - that any image will always be displayed on the video screen only according to its size in pixels - then you've got it right. But if 72 dpi is still of any interest, i'll explain some more.
For the video screen, and therefore obviously for web pages too, simply scan images at whatever resolution necessary to get the image size desired (pixels) from the area size of the original being scanned. This is very easily computed. The size of the image in pixels is all that matters on any video screen.
If you take an image from 35 mm film and the size of 35 mm film (36x24 mm, about 1.4x0.92 inches) is scanned at 72 dpi,you're going to get an image size of (1.4 inches x 72 dpi) x (0.92 inches x 72 dpi), which is about 100x66 pixels. Any 72 dpi scan of 35 mm film is not likely very useful, this is too small for most purposes, only thumbnail size. 72 dpi is simply not applicable. It just doesn't matter what the resolution was as long as it created the desired number of image pixels.
The display doesn't even look at the image dpi number when displaying the image on the screen. Screens only know about pixels. People in the chat room were mentioning this to me about my site taking too long to load..and i told them i just hadn't edited them properly. They kept telling me to knock down the dpi! People will say "Your pictures have to be 500 dpi, they can't be 50!) THAT is my point too. Remember, i'm not talking about printing here. All the images will appear 100x100 same appearance on your screen, on my screen, on any screen, including your browser or your photo editiing program. And this is the point; it shows that video systems simply do not use image dpi.
The difference in video screens and printers is that paper is dimensioned in inches, and printers do use dpi, and these images will all print on paper at very different sizes (printed from a photo editor NOT A WEBPAGE). Dpi is for printing, and your printer definitely will honor printing resolution to print individual images, and will print these individually at the sizes shown above (except your printer probably cannot handle the big one). But screens only show pixels.
I hope that makes sense, i have used up most of my free time, off to the bank in a few moments to set up the bank accounts for Collectibles for a Cause, Inc.
Ted
Regards,
Black Sox Fan
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* I'm smart enough to know that there are a lot of people who know more than I do.