Saving for Web – Image Size

"C Wright" wrote in message

This is a simple nit of a question. Often, when preparing images to be uploaded to the Web, we are advised to save them at 72ppi because that is the resolution of many older monitors. Along with that advice we are often
also told to restrict our images to a certain size, for example a long dimension of 600 pixels. Is there any point in doing both of these resizing
operations? If I save an image as, for example, a 600×400 pixel image it will appear at that absolute size on a monitor regardless of whether it is saved at a resolution of 72ppi or 150ppi! If the image were to be printed that, of course, could make a difference but if the only concern is to properly display the image on other’s monitors is there any point to resizing to both an absolute dimension AND a certain ppi size? Chuck

Just use the save for web function in Photoshop, put in your dimensions 600×400 or whatever – I don’t believe you are even asked for ppi

C Wright asks …

if the only concern is to properly display the image on other’s monitors is there any point to resizing to both an absolute dimension AND a certain ppi size?

No, as you say the ppi figure is meaningless for display purposes …

C Wright wrote:

This is a simple nit of a question. Often, when preparing images to be uploaded to the Web, we are advised to save them at 72ppi because that is the resolution of many older monitors. Along with that advice we are often also told to restrict our images to a certain size, for example a long dimension of 600 pixels. Is there any point in doing both of these resizing operations? If I save an image as, for example, a 600×400 pixel image it will appear at that absolute size on a monitor regardless of whether it is saved at a resolution of 72ppi or 150ppi! If the image were to be printed that, of course, could make a difference but if the only concern is to properly display the image on other’s monitors is there any point to resizing to both an absolute dimension AND a certain ppi size? Chuck

As the others have said, no. The pixel dimensions are all you should concern yourself with.

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In article <C09DD224.5BFB9%>,
C Wright wrote:

This is a simple nit of a question. Often, when preparing images to be uploaded to the Web, we are advised to save them at 72ppi because that is the resolution of many older monitors. Along with that advice we are often also told to restrict our images to a certain size, for example a long dimension of 600 pixels. Is there any point in doing both of these resizing operations? If I save an image as, for example, a 600×400 pixel image it will appear at that absolute size on a monitor regardless of whether it is saved at a resolution of 72ppi or 150ppi! If the image were to be printed that, of course, could make a difference but if the only concern is to properly display the image on other’s monitors is there any point to resizing to both an absolute dimension AND a certain ppi size?

No.

The people who tell you to save at 72 ppi do not understand resolution.

When an image is displayed in a Web browser, the Web browser strips off and disregards any ppi information. The only thing–the ONLY thing–that matters to a browser, any browser, is the total number of pixels. All Web browsers display an image at one pixel inthe image equals one pixel on the screen.

A 300×200 pixel image at 72 pixels per inch is absolutely, completely identical, in all Web browsers and on all platforms, to the same 300×200 pixel image at 96 pixels per inch, the same 300×200 pixel image at 300 pixels per inch, and the same 300×200 pixel image at 3,000,000 pixels per inch. For Web use, resolution in terms of pixels per inch is completely irrelevant.

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On Sat, 27 May 2006 14:53:40 GMT, C Wright
wrote:

This is a simple nit of a question. Often, when preparing images to be uploaded to the Web, we are advised to save them at 72ppi because that is the resolution of many older monitors. Along with that advice we are often also told to restrict our images to a certain size, for example a long dimension of 600 pixels.

This might help explain things:

http://www.ransen.com/Articles/DPI/Default.htm

and

http://www.ransen.com/Articles/MegaPixels/default.htm

http://www.ransen.com/

In article ,
Owen Ransen wrote:

On Sat, 27 May 2006 14:53:40 GMT, C Wright
wrote:

This is a simple nit of a question. Often, when preparing images to be uploaded to the Web, we are advised to save them at 72ppi because that is the resolution of many older monitors. Along with that advice we are often also told to restrict our images to a certain size, for example a long dimension of 600 pixels.

This might help explain things:

http://www.ransen.com/Articles/DPI/Default.htm

and

http://www.ransen.com/Articles/MegaPixels/default.htm

http://www.ransen.com/

It is my understanding that the human eye can’t distinguish much above 72 or perhaps 75 dpi, so for images that will be viewed on a monitor, but not printed, there’s no advantage to setting the resolution above this. For printing, though–and here my understanding isn’t so clear–it appears preferable to set images much higher, so settings of 600 or more shouldn’t be unreasonable. I don’t know if what I said about the human eye extends to printed pages or not.

On a somewhat related note, if scanning an image to bring into an image editing program, my instinct is to scan at a very high resolution, and then have the option to save/print edited versions at lower resolutions.

Hoping for further clarification here…
Happy computing,
Eric

—
For e-mail replies, please send to "thustar at yahoo dot com."

Eric P. wrote:

In article ,
Owen Ransen wrote:

On Sat, 27 May 2006 14:53:40 GMT, C Wright
wrote:

This is a simple nit of a question. Often, when preparing images to be uploaded to the Web, we are advised to save them at 72ppi because that is the resolution of many older monitors. Along with that advice we are often also told to restrict our images to a certain size, for example a long dimension of 600 pixels.

This might help explain things:

http://www.ransen.com/Articles/DPI/Default.htm

and

http://www.ransen.com/Articles/MegaPixels/default.htm

http://www.ransen.com/

It is my understanding that the human eye can’t distinguish much above 72 or perhaps 75 dpi, so for images that will be viewed on a monitor, but not printed, there’s no advantage to setting the resolution above this.

It’s actually ppi, not dpi at this stage. Most monitors now are around 96 ppi, a rule of thumb when setting pixel dimensions for monitor viewing.

For printing, though–and here my understanding
isn’t so clear–it appears preferable to set images much higher, so settings of 600 or more shouldn’t be unreasonable. I don’t know if what I said about the human eye extends to printed pages or not.

Most folks are fine with 300 or so ppi for printing, and it’s not clear that more ppi makes a discernable difference in final product, and it prints much slower. Here’s where dpi comes in: Some printers can be set to print at 360, 720, 1440 etc. dpi, all from the same image. Other printers may call it HQ, or fine, or medium, or draft, etc.

On a somewhat related note, if scanning an image to bring into an image editing program, my instinct is to scan at a very high resolution, and then have the option to save/print edited versions at lower resolutions.

That instinct is right! Unless you have dozens of images to scan and they will go only onto a web page….

—
John McWilliams

In article
,
"Eric P." wrote:

It is my understanding that the human eye can’t distinguish much above 72 or perhaps 75 dpi, so for images that will be viewed on a monitor, but not printed, there’s no advantage to setting the resolution above this. For printing, though–and here my understanding isn’t so clear–it appears preferable to set images much higher, so settings of 600 or more shouldn’t be unreasonable. I don’t know if what I said about the human eye extends to printed pages or not.

This is factually incorrect. The human eye can easily distinguish detail above 72 pixels per inch.

However, a monitor is a fixed pixel device. It is made up of a grid of pixels. A monitor who’s resolution is set to 72 pixels per inch always displays all images under all circumstances at 72 pixels per inch, without exception. A monitor who’s resolution is set to 96 pixels per inch always displays all images at 96 pixels per inch.

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"tacit" wrote in message

[…] A monitor who’s resolution is set to 96 pixels per inch always displays all images at 96 pixels per inch.

Tacit: Isn’t the Apple Cinema Display 120 ppi?

In article ,
tacit wrote:

In article
,
"Eric P." wrote:

It is my understanding that the human eye can’t distinguish much above 72 or perhaps 75 dpi, so for images that will be viewed on a monitor, but not printed, there’s no advantage to setting the resolution above this. For printing, though–and here my understanding isn’t so clear–it appears preferable to set images much higher, so settings of 600 or more shouldn’t be unreasonable. I don’t know if what I said about the human eye extends to printed pages or not.

This is factually incorrect. The human eye can easily distinguish detail above 72 pixels per inch.

There is an upper limit somewhere. I just don’t recall what it is.

However, a monitor is a fixed pixel device. It is made up of a grid of pixels. A monitor who’s resolution is set to 72 pixels per inch always displays all images under all circumstances at 72 pixels per inch, without exception. A monitor who’s resolution is set to 96 pixels per inch always displays all images at 96 pixels per inch.

I didn’t say anything to suggest that that’s not the case. Again, though, there’s an upper limit to a monitor’s resolution, due to physical limitations. I don’t know what that might be, either.

Thanks,
Eric

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For e-mail replies, please send to "thustar at yahoo dot com."

In article ,
"2" wrote:

Tacit: Isn’t the Apple Cinema Display 120 ppi?

The highest resolution Cinema Display has a pixel pitch of .25mm, which roughly translates into an effective resolution of about 96 pixels per inch in its highest resolution setting.

That seems reasonable to me, as anything higher resolution might make fine detail on the screen hard to view.

—
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In article ,
John McWilliams wrote:

Eric P. wrote:

In article ,
Owen Ransen wrote:

On Sat, 27 May 2006 14:53:40 GMT, C Wright
wrote:

This is a simple nit of a question. Often, when preparing images to be uploaded to the Web, we are advised to save them at 72ppi because that is the resolution of many older monitors. Along with that advice we are often
also told to restrict our images to a certain size, for example a long dimension of 600 pixels.

This might help explain things:

http://www.ransen.com/Articles/DPI/Default.htm

and

http://www.ransen.com/Articles/MegaPixels/default.htm

http://www.ransen.com/

It is my understanding that the human eye can’t distinguish much above 72 or perhaps 75 dpi, so for images that will be viewed on a monitor, but not printed, there’s no advantage to setting the resolution above this.

It’s actually ppi, not dpi at this stage. Most monitors now are around 96 ppi, a rule of thumb when setting pixel dimensions for monitor viewing.

I forgot how to assign this. My Monitors cp allows me to select resolutions at certain refresh rates, but I don’t see where to assign a "per inch" setting.

For printing, though–and here my understanding
isn’t so clear–it appears preferable to set images much higher, so settings of 600 or more shouldn’t be unreasonable. I don’t know if what I said about the human eye extends to printed pages or not.

Most folks are fine with 300 or so ppi for printing, and it’s not clear that more ppi makes a discernable difference in final product, and it prints much slower. Here’s where dpi comes in: Some printers can be set to print at 360, 720, 1440 etc. dpi, all from the same image. Other printers may call it HQ, or fine, or medium, or draft, etc.

On a somewhat related note, if scanning an image to bring into an image editing program, my instinct is to scan at a very high resolution, and then have the option to save/print edited versions at lower resolutions.

That instinct is right! Unless you have dozens of images to scan and they will go only onto a web page….

Oh, yes. In the case of .jpg files, I choose Save for Web in Photoshop. For .gif files, I don’t like to alter things too much, because the more I do, the more degradation in quality I see.

Thanks,
Eric

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For e-mail replies, please send to "thustar at yahoo dot com."

"tacit" wrote in message

The highest resolution Cinema Display has a pixel pitch of .25mm, which roughly translates into an effective resolution of about 96 pixels per inch in its highest resolution setting.

Thanks for that. I thought I recalled a control-panel monitor setting of 120.

That seems reasonable to me, as anything higher resolution might make fine detail on the screen hard to view.

That must have something to do with the way the image is formed, because we don’t have trouble seeing more detail on paper. FWIW, tests have shown that while the human eye has a nominal ‘resolution’ of 6 lp/mm it can often tell when an image (especially of type) is of a higher resolution; it can’t count the lp/mm, only sense the difference.

"Eric P." wrote in message

In article ,
John McWilliams wrote:

Eric P. wrote:

In article ,
Owen Ransen wrote:

On Sat, 27 May 2006 14:53:40 GMT, C Wright
wrote:

This is a simple nit of a question. Often, when preparing images to be
uploaded to the Web, we are advised to save them at 72ppi because that is
the resolution of many older monitors. Along with that advice we are often
also told to restrict our images to a certain size, for example a long
dimension of 600 pixels.

This might help explain things:

http://www.ransen.com/Articles/DPI/Default.htm

and

http://www.ransen.com/Articles/MegaPixels/default.htm

http://www.ransen.com/

It is my understanding that the human eye can’t distinguish much above 72 or perhaps 75 dpi, so for images that will be viewed on a monitor, but not printed, there’s no advantage to setting the resolution above this.

It’s actually ppi, not dpi at this stage. Most monitors now are around 96 ppi, a rule of thumb when setting pixel dimensions for monitor viewing.

I forgot how to assign this. My Monitors cp allows me to select resolutions at certain refresh rates, but I don’t see where to assign a "per inch" setting.

For printing, though–and here my understanding
isn’t so clear–it appears preferable to set images much higher, so settings of 600 or more shouldn’t be unreasonable. I don’t know if what I said about the human eye extends to printed pages or not.

Most folks are fine with 300 or so ppi for printing, and it’s not clear that more ppi makes a discernable difference in final product, and it prints much slower. Here’s where dpi comes in: Some printers can be set to print at 360, 720, 1440 etc. dpi, all from the same image. Other printers may call it HQ, or fine, or medium, or draft, etc.

On a somewhat related note, if scanning an image to bring into an image editing program, my instinct is to scan at a very high resolution, and then have the option to save/print edited versions at lower resolutions.

That instinct is right! Unless you have dozens of images to scan and they will go only onto a web page….

Oh, yes. In the case of .jpg files, I choose Save for Web in Photoshop. For .gif files, I don’t like to alter things too much, because the more I do, the more degradation in quality I see.

Thanks,
Eric

—
For e-mail replies, please send to "thustar at yahoo dot com."

"Eric P." wrote in message

I forgot how to assign this. My Monitors cp allows me to select resolutions at certain refresh rates, but I don’t see where to assign a "per inch" setting.

Well, it really shouldn’t ever be put in such terms, but if you are using XP, then just right-click on the desktop, then take Properties, then the Settings tab. Click in there on Advanced and (daminit) there’s "DPI" settings (96, 120, custom). Go crazy and take the Custom settings, like 20%, and see how silly it can get.

In article ,
John McWilliams writes:

…Most monitors now are around 96 ppi, a rule of thumb
when setting pixel dimensions for monitor viewing.

That’s not a useful "rule of thumb". The monitors I use range from about 32 to 120 ppi. But although you may well be interested in a web user’s total screen resolution (say, 1024×768 or 800×600), there’s no reason you should care how many pixels their monitors have per inch.
—

Warren S. Sarle SAS Institute Inc. The opinions expressed here SAS Campus Drive are mine and not necessarily
(919) 677-8000 Cary, NC 27513, USA those of SAS Institute.

In article ,
"Eric P." writes:

It is my understanding that the human eye can’t distinguish much above 72 or perhaps 75 dpi, …

The resolving power of the human eye varies greatly from person to person, especially at close distances, but a typical value for a young person with good vision would be in the neighborhood of 150 to 250 lines per inch. And a line requires at least two pixels.

—

Warren S. Sarle SAS Institute Inc. The opinions expressed here SAS Campus Drive are mine and not necessarily
(919) 677-8000 Cary, NC 27513, USA those of SAS Institute.

"2" wrote in message
SNIP

FWIW, tests have shown that while the human eye has a nominal ‘resolution’ of 6 lp/mm it can often tell when an image (especially of type) is of a higher resolution; it can’t count the lp/mm, only sense the difference.

It’s called Vernier acuity:
< http://www.photonicshistory.com/directory/dictionary/lookup. asp?url=lookup&entrynum=5559&letter=v>
as relative to visual acuity:
< http://www.photonicshistory.com/directory/dictionary/lookup. asp?url=lookup&entrynum=5605&letter=v>

So according to that source, Vernier acuity is about 6x higher than visual acuity, which is why typeface needs to be printed at much higher resolution than continuous tone images.

Bart

In article ,
"2" wrote:

That must have something to do with the way the image is formed, because we don’t have trouble seeing more detail on paper.

It has to do with the assumptions that programmers make when they design user interface controls, more likely.

User interface objects on a computer screen are often designed to be a certain number of pixels in size; for example, the standard size of a button is typically 20 pixels high. If a screen has a resolution of 200 pixels per inch, that makes the size of a button one-tenth of an inch high.

Now, it’s easy to see an object one-tenth of an inch high on paper. But we typically look at a sheet of paper from a much closer distance than we look at a computer monitor–and a sheet of paper isn’t glowing, it’s using reflected light. Looking at an object a tenth of an inch high on a glowing screen that’s much farther away is a whole ‘nother story. 🙂

A computer screen that had a higher resolution but did not make the objects smaller would probably look significantly better. If the size of a button were the same on a 200 pixel per inch screen, say, and the button were composed of more pixels, it’d probably look quite good. But that’d involve dramatically re-thinking the way things are displayed on a screen.

The Mac uses PDF (in OS X) or QuickDraw (in older versions) to draw images on the screen,a nd it is possible for a programmer to write a program that would display its user interface elements and text and so forth on the screen at the same physical size regardless of the resolution of the monitor if he so chose, because both PDF and QuickDraw are resolution independent. (He wouldn’t be able to use pre-built OS controls; he’d have to draw them himself.) On Windows, which does not have a resolution-independent system for displaying things on the screen, it’d be much more difficult. (Windows Vista was supposed to include this kind of functionality, but Microsoft has announced that it has been dropped.)

—
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In article
,
"Eric P." wrote:

I forgot how to assign this. My Monitors cp allows me to select resolutions at certain refresh rates, but I don’t see where to assign a "per inch" setting.

When you set different resolutions, you are setting different "per inch" settings.

Let us say that your monitor is, for example, ten inches wide. If you set your monitor to 1024×768, it would be 102.4 pixels per inch. If you set it to 640×480, it owuld be 64 pixels per inch. If you set it to 800×600, it would be 80 pixels per inch.

Pixels per inch is the number of pixels divided by the number of inches, that’s all.

—
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"tacit" wrote in message

The Mac uses PDF (in OS X) or QuickDraw (in older versions) to draw images on the screen,a nd it is possible for a programmer to write a program that would display its user interface elements and text and so forth on the screen at the same physical size regardless of the resolution of the monitor if he so chose, […]

neXt used Postscript display. I wish I had seen it IRL.

Warren Sarle wrote:

In article ,
John McWilliams writes:

…Most monitors now are around 96 ppi, a rule of thumb
when setting pixel dimensions for monitor viewing.

That’s not a useful "rule of thumb". The monitors I use range from about 32 to 120 ppi. But although you may well be interested in a web user’s total screen resolution (say, 1024×768 or 800×600), there’s no reason you should care how many pixels their monitors have per inch.

Not useful to/for you. But 96.43% of all non-specialist non-academia-centric monitors fall between 72 and 96 ppi.

—
john mcwilliams

In article , John
McWilliams wrote:

Warren Sarle wrote:

In article ,
John McWilliams writes:

…Most monitors now are around 96 ppi, a rule of thumb
when setting pixel dimensions for monitor viewing.

That’s not a useful "rule of thumb". The monitors I use range from about 32 to 120 ppi. But although you may well be interested in a web user’s total screen resolution (say, 1024×768 or 800×600), there’s no reason you should care how many pixels their monitors have per inch.

Not useful to/for you. But 96.43% of all non-specialist non-academia-centric monitors fall between 72 and 96 ppi.

And 92.76% of all statistics are made up on the spur of the moment.

Jeremy

Jeremy Roussak wrote:

In article , John
McWilliams wrote:

Warren Sarle wrote:

In article ,
John McWilliams writes:

…Most monitors now are around 96 ppi, a rule of thumb
when setting pixel dimensions for monitor viewing.

That’s not a useful "rule of thumb". The monitors I use range from about 32 to 120 ppi. But although you may well be interested in a web user’s total screen resolution (say, 1024×768 or 800×600), there’s no reason you should care how many pixels their monitors have per inch.

Not useful to/for you. But 96.43% of all non-specialist non-academia-centric monitors fall between 72 and 96 ppi.

And 92.76% of all statistics are made up on the spur of the moment.

And spuriously accurate! Now it’s 92.77%.

—
John McWilliams

"Warren Sarle" wrote in message
|
| In article ,
| "Eric P." writes:
| >
| > It is my understanding that the human eye can’t distinguish much | > above 72 or perhaps 75 dpi, …
|
| The resolving power of the human eye varies greatly from person | to person, especially at close distances, but a typical value for | a young person with good vision would be in the neighborhood of | 150 to 250 lines per inch. And a line requires at least two pixels. |

A simple empirical test is to take a ruler with fine divisions and see if you can resolve them. I have no trouble (with my glasses on) seeing either 1/64" or 1/100". That’s at least a lower limit of 100 lpi. If you have a good printer and a decent graphics program you can make your own charts.

Norm

In article ,
tacit wrote:

In article
,
"Eric P." wrote:

I forgot how to assign this. My Monitors cp allows me to select resolutions at certain refresh rates, but I don’t see where to assign a "per inch" setting.

When you set different resolutions, you are setting different "per inch" settings.

Let us say that your monitor is, for example, ten inches wide. If you set your monitor to 1024×768, it would be 102.4 pixels per inch. If you set it to 640×480, it owuld be 64 pixels per inch. If you set it to 800×600, it would be 80 pixels per inch.

Pixels per inch is the number of pixels divided by the number of inches, that’s all.

OK, I was confused between pixels and dots. I’m pretty sure that an aperture grill can’t be made to be nearly as high as some of those higher resolutions.

And I used to know all this stuff…’specially when I worked at Radius! Oh, well, I’ve slept since then 😉

Thanks,
Eric

—
For e-mail replies, please send to "thustar at yahoo dot com."

In article ,
John McWilliams wrote:

Jeremy Roussak wrote:

In article , John
McWilliams wrote:

Warren Sarle wrote:

In article ,
John McWilliams writes:

…Most monitors now are around 96 ppi, a rule of thumb
when setting pixel dimensions for monitor viewing.

That’s not a useful "rule of thumb". The monitors I use range from about 32 to 120 ppi. But although you may well be interested in a web user’s total screen resolution (say, 1024×768 or 800×600), there’s no reason you should care how many pixels their monitors have per inch.

OK, so is there a relationship between ppi/dpi and refresh rate? Or am I merely complicating matters further by wondering about it? *L*

Thanks,
Eric

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In article
,
"Eric P." wrote:

OK, so is there a relationship between ppi/dpi and refresh rate? Or am I merely complicating matters further by wondering about it? *L*

No. Refresh rate has nothing whatsoever to do with PPI, DPI, or resolution.

Your monitor image is not steady. The picture on your monitor flashes. The refresh rate is a measure of how fast the picture flashes. 60Hz means it flashes 60 times every second, 85 Hz means the image flashes 85 times per second, and so on.

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