My question is this: My sharpening actions don't include reducing the DPI of my images from 360 to 72 for web viewing. I manually do that after the image has been reduced in size and sharpened for the web and before it is saved as a JPEG. I can't tell if this actually affects the quality of the image for web viewing. Does it? Are there any other advantages to doing this besides reducing the file size and protecting your image from those wishing to save as a copy? Also, what if I changed the DPI to 1000 after sharpening? Does it actually make image look sharper for the web? I am curious to how y'all handle that and your thoughts... Thanks so much for your time.
First, a little clarification that always drives me crazy:
DPI: Dots Per Inch, this is printer output terminology
PPI: Pixels Per Inch, this is computer output terminology (determines print size)
(The distinction is most relevant to inkjet printers, not Chromira/Lightjet, where they are actually just about the same thing, I believe)
Your PPI, however, has nothing to do with how a web image is viewed, or sharpened, all that matters is the number of pixels. An 800 pixel image is 800 pixels on the monitor regardless of the PPI. The PPI determines how large the image would be if it were printed (and that PPI is converted to DPI by the printer). I never pay attention to PPI until I'm dealing with a print file. Changing the PPI won't alter the file size, or protect your image, either.
For example, if you have a 720 pixel image it'll be 720 pixels on the web. If set to 360 PPI, it will print out to 2 inches. Your printer could have an output resolution of 1200 DPI, but it'll still be 2 inches, just have very smooth transitions.
Hope that helps
Posted by David Bostedo on January 7, 2010 at 8:38 AM
Michael - The "72" ppi (commonly dpi) thing is one of my pet peeves, and I started a good discussion about it on here a little while back.
To re-iterate what Floris said, you're ppi setting for your web/screen image is completely ignored. You don't need to set it to anything at all. An 800x600@72 ppi image is exactly the same on your computer screen as an 800x600@72000 ppi image.
Posted by Jim Bullard on January 7, 2010 at 9:23 AM
The discussion linked above is good but to be really anal, should you care at all which you don't need to except when sharpening while using CS3 or earlier and/or a non-open GL 2 compatible video card, the old "72 ppi" for screen resolution is not accurate and hasn't been for years. That harks back to VGA days. Screen resolution varies these days. If you really want to know the ppi for your screen measure the width of the actual display area then divide that by the pixel width you've set your screen resolution for. Do the same with the height. They should come out the same or very close. If not the same average the two and that is your screen ppi. My laptop is 98 ppi and my desktop is 94 ppi. Most screens these days are in the 90s or low 100s, not 72.
Thanks guys I really appreciate it. That's just one less thing I don't need to fool with anymore.
Posted by Wick Smith on January 8, 2010 at 8:36 AM
I have to jump in on this one. The discussion on the DPI/PPI regarding size is good and accurate I'm sure. As far as the quality of the image, there are some issues. Most print applications require a 300 DPI resolution image for clarity. That makes for larger file sizes, but with print, who cares. On the web, the vast majority of monitors can only show 72 dots per inch, and a few can go up to 96 dpi. If you optimize for the web, and use anything higher than 72 DPI, you are only increasing the file size, and not increasing the image quality, as the computer screens can't display the additional resolution.
Posted by David Bostedo on January 8, 2010 at 11:48 AM
On the web, the vast majority of monitors can only show 72 dots per inch, and a few can go up to 96 dpi. If you optimize for the web, and use anything higher than 72 DPI, you are only increasing the file size, and not increasing the image quality, as the computer screens can't display the additional resolution.
Wick - That's just not correct, and not really the right way to think of things.
First, all that matters for the web is the actual resolution in pixels. As stated above, the dpi (ppi really) can be ignored. The computer won't use it for anything. The ppi of the monitor has nothing to do what's shown on screen. If, and only if, you're trying to get an image to show up at an actual physical dimension on someone's screen (say a measurable 5x7 on the screen), then you need to know the ppi of the screen and map to that. (And screen sizes and ppi's vary widely.) In that case you would simply be using ppi to determine the pixel resolution you want, which is all the computer cares about.
You're correct, that arbitrarily increasing resolution won't buy you anything, since the screen is limited in what it can show. But it's much clearer and easier to ignore the physical size that the image will show up at - since it's largely unknowable - and focus on the pixel resolution.
Second, I don't think there's been an computer LCD monitor made in a while as low as 72 ppi. Think of it this way - a 720 pixel vertical resolution screen - which is pretty low, like a small laptop - would be 10 inches tall at 72 ppi. And that's a lot bigger than most 720 screens, meaning their ppi is much higher.
The screen I'm working on is a 16 inch laptop, with a resolution of 1920x1080 and a physical size of 13.94 inches by 7.81 inches. That works out to ppi's of 137 horizontally and 138 vertically. I'm guessing a bit, but I think most monitors these days are between 95 and 150 ppi.
Posted by Richard Ditch on January 9, 2010 at 5:39 PM
This has come up many times before her at NPN and elsewhere, and I've written about it many times here and elsewhere. And I'm tired of writing the same thing many times here and elsewhere so I've written it out in detail in the articles on my web site.
Floris and David are correct - dpi has nothing to do with how an image appears in a web browser. Onlt the totla pixels long by high matter.
And I've posted examples of the same image at different ppi settings in this thread where I explained to Wick that he was wrong in exactly the same way he continues to be wrong here. That was back in July, so Wick please take a look at my examples so I don't feel obligated to point this out to yet yet again.
Discussion
7 repliesDPI: Dots Per Inch, this is printer output terminology
PPI: Pixels Per Inch, this is computer output terminology (determines print size)
(The distinction is most relevant to inkjet printers, not Chromira/Lightjet, where they are actually just about the same thing, I believe)
Your PPI, however, has nothing to do with how a web image is viewed, or sharpened, all that matters is the number of pixels. An 800 pixel image is 800 pixels on the monitor regardless of the PPI. The PPI determines how large the image would be if it were printed (and that PPI is converted to DPI by the printer). I never pay attention to PPI until I'm dealing with a print file. Changing the PPI won't alter the file size, or protect your image, either.
For example, if you have a 720 pixel image it'll be 720 pixels on the web. If set to 360 PPI, it will print out to 2 inches. Your printer could have an output resolution of 1200 DPI, but it'll still be 2 inches, just have very smooth transitions.
Hope that helps
To re-iterate what Floris said, you're ppi setting for your web/screen image is completely ignored. You don't need to set it to anything at all. An 800x600@72 ppi image is exactly the same on your computer screen as an 800x600@72000 ppi image.
Wick - That's just not correct, and not really the right way to think of things.
First, all that matters for the web is the actual resolution in pixels. As stated above, the dpi (ppi really) can be ignored. The computer won't use it for anything. The ppi of the monitor has nothing to do what's shown on screen. If, and only if, you're trying to get an image to show up at an actual physical dimension on someone's screen (say a measurable 5x7 on the screen), then you need to know the ppi of the screen and map to that. (And screen sizes and ppi's vary widely.) In that case you would simply be using ppi to determine the pixel resolution you want, which is all the computer cares about.
You're correct, that arbitrarily increasing resolution won't buy you anything, since the screen is limited in what it can show. But it's much clearer and easier to ignore the physical size that the image will show up at - since it's largely unknowable - and focus on the pixel resolution.
Second, I don't think there's been an computer LCD monitor made in a while as low as 72 ppi. Think of it this way - a 720 pixel vertical resolution screen - which is pretty low, like a small laptop - would be 10 inches tall at 72 ppi. And that's a lot bigger than most 720 screens, meaning their ppi is much higher.
The screen I'm working on is a 16 inch laptop, with a resolution of 1920x1080 and a physical size of 13.94 inches by 7.81 inches. That works out to ppi's of 137 horizontally and 138 vertically. I'm guessing a bit, but I think most monitors these days are between 95 and 150 ppi.
Floris and David are correct - dpi has nothing to do with how an image appears in a web browser. Onlt the totla pixels long by high matter.
And I've posted examples of the same image at different ppi settings in this thread where I explained to Wick that he was wrong in exactly the same way he continues to be wrong here. That was back in July, so Wick please take a look at my examples so I don't feel obligated to point this out to yet yet again.