I always thought that 72 dpi (or ppi if you want to split hairs) was standard resolution for resized images to be displayed on the web. But I've also seen images resized at 96 dpi and I'd like to know why and which one is best?
It doesn't matter, except in one case. If you have text in your image (copyright and your signature, for example) the resolution should be set at 72 dpi so that the text will display at the correct size.
-Preston
Posted by David A Bliss on August 31, 2007 at 12:31 PM
Preston, I'm sorry to disagree with you, but I have text in images at many different dpi, and have never had a problem. I have even reduced image size after I have added text without any problems.
72 dpi (ppi) used to be the standard monitor resolution. Any more, 96 dpi is standard. This is why you see many web jpegs set at 96 dpi.
Posted by Mark Stahlke on August 31, 2007 at 2:47 PM
I think Preston got it right with a minor quibble. The monitor doesn't know anything about inches. It understands pixels. 800 pixels is 800 pixels whether the DPI (or PPI if you prefer) is 72 or 96 or 10 million.
Printers, on the other hand, do care about inches because the document size is specified in inches (or millimeters in some backwards parts of the world ). When you send a 72 DPI file to a printer you'll get a different size print than when you send a 96 DPI file.
As for the text, and here is my minor quibble, once the text is merged into to the image by flattening layers or saving as a JPEG the text isn't really text anymore. It's a part of the image that just happens to look like letters. In other words, the text will be rendered as an image not as a font. As such, it will scale just as well (or poorly) as the rest of the image.
Thanks Guys, That clears it up for me. The reason I was asking is because I'm getting more requests from people who want to browse my work on line in the comfort of their own home. So I'm finally going to get around to setting up a web page with an online host. However, I won't upload full size files; 800x600 will be the maximum but I want to display decent quality at that resolution, so 96 dpi it is then.
I think you still missed the point about dpi. It doesn't make one bit of difference as far as displaying the image on a monitor. Pixes ARE pixels
Some image print programs, i.e. Photoshop, use the dpi to calculate the size of the image for printing, That is a hold over from the journalistic background of Adobe. Other image softtware, i.e. Q-Image, print an image by the dimensions, not by the resolution. For all practical purposes, the resolution of most printers is around 300 dpi. We always save our images at 300 dpi whether they will be displayed on a monitor or printed
As far as 72 vs 96 dpi, furgidaboudid!
If you want to make certain that people are not illegally printing your images, then you might want to set the resolution at 6000 dpi. Granted, it may not work all of the time, but it will make people have to work harder if they attempt to print an image at its native resolution.
As far as having to use 72 dpi to properly display text, it doesn't make any difference. In order to save an image as a JPEG for the Internet, it must be flattened. Once that is done, the text has become fixed in the pixes and its relative size will no longer vary no matter the monitor resolution.
As mentioned above, when using Photoshop we save our images to be printed at the resolution of the printer which is 314 dpi. The location and size of the text is the same on the print as on the monitor.
I've always resized anything for the web at 72 dpi until recently, when I found a freeware program that would resize my images to 640X480, add a water mark and save the new images in to a new file. It makes them all at 96 dpi, but it saves me several steps, and a lot of time. I can select all or just a few files from a folder. It makes things quick and easy, I like quick and easy.
Tim
Posted by David Bostedo on August 31, 2007 at 8:31 PM
Tim - I just want to make sure everyone who may be reading this is clear, based on what you said. The dpi that you list (96, or 72) has NO meaning, at all, to the actual resolution of your file, or how it appears in PS or on the web. You could make it 10,000,000 dpi, and it would look exactly the same. The only difference would be that PS would report your image size in inches differently (even though it would look and store it the same) and a printer may print it very tiny. But the photo resolution and how it appears on screen would not change.
Posted by Tim Behle on August 31, 2007 at 10:19 PM
David,
Not wanting to argue, just learn. Why is it that if I save two photo's at 640X480, one at 72 DPI and one at 300 DPI, that folks on a dial up connection can tell a noticeable difference in load time? And if I crank up the size, the 72 DPI turns into a bunch of colored squares, while the 300 dpi file remains clear?
Posted by David Foster on August 31, 2007 at 11:28 PM
It couldn't. Since both files would 900k each (uncompressed, and disregarding file overhead) there could be no difference in xfer time. You can prove it to yourself by creating that size new document in Photoshop. Set the height/width to 640x480 and then enter anything you like into the resolution field. Because file contains a constant number of pixelsÐ307200, the size remains the same, and they will display at exactly the same size in your browser.
Some Internet Service Providers "increase" their dial up speed by removing bytes of data from files. The result is a blocky looking image. If all of the data were properly transmitted, then the images would be identical. This is proof that one gets what one pays for. Having a cheap "higher speed" dial up service versus a more expensive dial up without "compression" or a broadband connection does result in the lose of data. It may be that their algorithm does look at the resolution and then figures that it must transmit all of the data at 300 dpi while it removes data at 72 dpi. Either way, the moral is not to size for the monitor at 72, 96 or whatever dpi, but at the printer resolution of 300 dpi or more.
Posted by David A Bliss on August 31, 2007 at 11:54 PM
Ok, I have come back to this thread tonight after doing some research (meaning, changing some files and saving them). While I know quite a bit about pixels and bit depth as it relates to calculating file size and printing, I now have to admit I didn't know much about dpi in relation to resizing file size and display. The funny thing was, I actually did the tests before I read the posts by David (and David... There are a lot of David's here, aren't there... )
You are absolutely correct. dpi means absolutely nothing in relation to file size or display. I always like when I learn things, but I have to admit I feel a little silly that I had never put this together before now. It actually makes total sense, given that I understand about dpi and print size when not resampling the image.
Thanks for making me think!
Posted by Tim Behle on September 1, 2007 at 2:40 AM
Making me think is right. I had always considered that reducing anything to be posted on the web, down to 72 DPI, would add a little protection to my photo ( Along with making things quicker for folks on dial up ). If you steal a photo at 72 dpi and then blow it up, it looks terrible. Now you are telling me that it makes no difference as to what DPI I save to. Other than adding a watermark, what can I do to protect them?
You are correct that 72 dpi may not protect an image. It may only work if the ISP (internet service provider) strips out some of the data so as to "speed up" the download. If one downloads an image and gets all of the data, then Q-Image would have no problem printing it. The user may have a problem with Photoshop, but I am certain that if they have been stealing images to print that they will have figured out how to circumvent the 72 dpi setting.
The moral is that we cannot trust anyone, be it someone surfing the web or an ISP.
Discussion
15 repliesThanks
Bob
It doesn't matter, except in one case. If you have text in your image (copyright and your signature, for example) the resolution should be set at 72 dpi so that the text will display at the correct size.
-Preston
72 dpi (ppi) used to be the standard monitor resolution. Any more, 96 dpi is standard. This is why you see many web jpegs set at 96 dpi.
Printers, on the other hand, do care about inches because the document size is specified in inches (or millimeters in some backwards parts of the world
As for the text, and here is my minor quibble, once the text is merged into to the image by flattening layers or saving as a JPEG the text isn't really text anymore. It's a part of the image that just happens to look like letters. In other words, the text will be rendered as an image not as a font. As such, it will scale just as well (or poorly) as the rest of the image.
Thankyou
Bob
I think you still missed the point about dpi. It doesn't make one bit of difference as far as displaying the image on a monitor. Pixes ARE pixels
Some image print programs, i.e. Photoshop, use the dpi to calculate the size of the image for printing, That is a hold over from the journalistic background of Adobe. Other image softtware, i.e. Q-Image, print an image by the dimensions, not by the resolution. For all practical purposes, the resolution of most printers is around 300 dpi. We always save our images at 300 dpi whether they will be displayed on a monitor or printed
As far as 72 vs 96 dpi, furgidaboudid!
If you want to make certain that people are not illegally printing your images, then you might want to set the resolution at 6000 dpi. Granted, it may not work all of the time, but it will make people have to work harder if they attempt to print an image at its native resolution.
As far as having to use 72 dpi to properly display text, it doesn't make any difference. In order to save an image as a JPEG for the Internet, it must be flattened. Once that is done, the text has become fixed in the pixes and its relative size will no longer vary no matter the monitor resolution.
As mentioned above, when using Photoshop we save our images to be printed at the resolution of the printer which is 314 dpi. The location and size of the text is the same on the print as on the monitor.
-PB
I've always resized anything for the web at 72 dpi until recently, when I found a freeware program that would resize my images to 640X480, add a water mark and save the new images in to a new file. It makes them all at 96 dpi, but it saves me several steps, and a lot of time. I can select all or just a few files from a folder. It makes things quick and easy, I like quick and easy.
Tim
Not wanting to argue, just learn. Why is it that if I save two photo's at 640X480, one at 72 DPI and one at 300 DPI, that folks on a dial up connection can tell a noticeable difference in load time? And if I crank up the size, the 72 DPI turns into a bunch of colored squares, while the 300 dpi file remains clear?
Some Internet Service Providers "increase" their dial up speed by removing bytes of data from files. The result is a blocky looking image. If all of the data were properly transmitted, then the images would be identical. This is proof that one gets what one pays for. Having a cheap "higher speed" dial up service versus a more expensive dial up without "compression" or a broadband connection does result in the lose of data. It may be that their algorithm does look at the resolution and then figures that it must transmit all of the data at 300 dpi while it removes data at 72 dpi. Either way, the moral is not to size for the monitor at 72, 96 or whatever dpi, but at the printer resolution of 300 dpi or more.
You are absolutely correct. dpi means absolutely nothing in relation to file size or display. I always like when I learn things, but I have to admit I feel a little silly that I had never put this together before now. It actually makes total sense, given that I understand about dpi and print size when not resampling the image.
Thanks for making me think!
What is compression and how does it work?
You are correct that 72 dpi may not protect an image. It may only work if the ISP (internet service provider) strips out some of the data so as to "speed up" the download. If one downloads an image and gets all of the data, then Q-Image would have no problem printing it. The user may have a problem with Photoshop, but I am certain that if they have been stealing images to print that they will have figured out how to circumvent the 72 dpi setting.
The moral is that we cannot trust anyone, be it someone surfing the web or an ISP.