 Ariel Lepor |
Web colors & PPI Hi BetterPhoto friends, Two questions: 1. I've seen things in different programs and forums about saving in web colors for uploading pictures to the web. Not all programs have this ability. Is this only when saving as GIF? I thought web browsers are capable of showing images. 2. Some people mention saving in a certain DPI (usu. 72 dpi) along with inches. I know that this simply equates to a certain pixel size. But is this 100% the same as saving as a certain pixel size? Do some programs show the image at the inches specified when the number is different from the screen's DPI? Thanks,
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robert G. Fately |
1. The number of colors that can be displayed over the web is more limited than the number that can be viewed on a screen or in a print, Ariel. These are rather subtle differences for the most part, and if you don't view a side-by-side comparison it often is unnoticeable. If you don't "save for web" (either because you don't want to or the program doesn't offer the option) then the browser and screen drivers will simply make the choices when a user looks at the image anyway. By "aving for web" you are having your editing program pre-define the colors that the browser should display to the viewer. 2. First, you must remember that screens have much lower resolution capability than printers - usually around 72dpi (or up to 95dpi). So here's what's happening: say you have an image of a square postage stamp 1" on a side that you scanned in at 300ppi. If you display that image on your screen (for easy math, let's assume your screen's native resolution is 75dpi) one of two things will happen. Either the stamp will appear as a 4" square - because the screen driver is displaying every pixel and there are, of course, 300 pixels per inch in the scan. Or, the stamp will appear as a 1" square - meaning that the screen driver has opted to ignore 3 out of 4 pixels and only show you 75 of the 30 in the original image. So by saving (in this hypothetical case) at 75dpi you have pre-empted the driver and defined the image in the resolution of the screen. Now if you take that 75dpi image and display it on a screen with a native resolution of 95dpi, the stamp will appear as less than 1 inch on a side - precisely 75/95th's of an inch. The size of an actual pixel on any screen is unchangeable - but the variation of different screens means that you'll rarely see stated dimensions that match what you are looking at onscreen.
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Ariel Lepor |
So for number 1, are you saying you really don't have to bother with saving for web? And for number 2, are you saying that saving "72 dpi with 3x4 inches" doesn't put this specif information into the picture, but rather just makes the image 216x288 pixels?
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robert G. Fately |
For #1, essentially - yes. SInce there are so many other variables in terms of the colors the person browsing to your image will actually see (type of monitor, age of monitor, ambient light, etc.) subtle changes will probably not mean much in the scheme of things. FOr #2 - if you "tell" a program to save at 72dpi AND 3x4 inches then the final image will of course be216x288.
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