When a low resolution photo is reqested for review by a publisher, what is the best resolution to save the file at. This is a new area for me and I wasnt sure what to do.
I save and send mine at 96 dpi. I read that a lot of PC monitors resolve to 96 dpi, while many Macs go to 72 dpi, so I opted for the slightly higher res. I've sold some images by offering 96 dpi proofs that way, and haven't heard any complaints that resolution wasn't high enough. Anyone know for sure if the 96/72 thing is accurate?
Of course, ppi rather than dpi. My bad. I use them interchangeably sometimes, though I know better.
The question remains, however. So let's talk ppi, not dpi, since we're not talking about print. Help me out here. If I size a horizontal to 800 pixels across, what ppi resolution should I choose, and why? While things have been working just fine the way I've been doing it, I'd rather know the ins and outs than not know.
And so it really doesn't matter whether I choose 20 ppi or 200 ppi at 800 pixels across when looking at a photo on my monitor? If true, that's at least counterintuitive, and sounds just wrong. How can it not matter how many pixels per inch I tell the image to be at 800 pixels across? Or did I misunderstand Darren's and Guy's explanation.
I mean, telling someone to size an image to 800 pixels on the long side without adding which ppi setting is most appropriate for computer screen viewing seems a bit like asking someone to calculate the square footage of a floor with only one of the two required measurements.
Steve - it's not counterintuitive if you realize that monitor software (not the screen itself) only cares about the number of pixels, and has no concept of inches at all (in terms of what we're talking about). So ppi and dpi can't mean anything in this case. Think of it this way - if you display (at 100%) an 800x600 image on a monitor set to 800x600 resolution, it will fill the screen (regardless of your monitor size). If you up the resolution setting in your OS to 1024x768, it will now fill less of the screen, even though the dpi/ppi are the same. All that matters is the 800x600 size, and the resolution settings.
(AS an aside, monitors do have a native dpi, but this refers to the absolute maximum resolution you can set the monitor to - so that every physical pixel is used as a pixel in the OS. At smaller resolutions, multiple physical pixels are used for each software pixel.)
OK, David, I'll take your word for that. Makes sense. Now, when I size an image to 800 pixels across in Photoshop, which ppi setting should I choose? If it really isn't an important measurement, can I select zero? Well, I know I can't. If I size an image to 800 pixels across and set it at 20 ppi, it pixelates badly. There's not enough data to sharply resolve the image on my screen. So I'm still confused as to which ppi setting is best. As I increase the ppi settings, the image quality improves on my screen, but my assumption is that I'll reach and eventually exceed the monitor's (monitor software's) ability to further resolve the image, so I wonder where that ppi point is.
We have fallen in the habit of using NPN's old posting guideline (640x480 @72ppi) for all our low resolution needs. Clients have no complaints, and it's a convenient size for all our management/tracking work.
Steve - I don't have CS2/3, only Elements. However if I specify 800x600 in Elements, the ppi setting doesn't matter - I get the same image regardless (I usually leave that field blank, actually). I suppose It's possible that other software might be doing something funny to try to relate ppi to your monitor size/video card/jpeg compression. If that's the guess, then that is a function of how they display the image, not the image itself.
My best guess, though, is that it's using the scale/ruler that's built in to Photoshop. My pictures stright out of camera show up as 14.4" x 10.8" (I think) which is completely arbitrary based on 5 MPixels and a completely arbitrary choice by Canon to encode 180 ppi. Note that Canon could have chosen any ppi to encode, and Photoshop would just adjust the ruler size of my image to compensate. (I.e. if they had chosen 90, my photo would seem to be 28.8"x21.6" in Photoshop.)
Now if this scale is being used, and you set a ppi, it could be stretching/shrinking you image in weird ways. However, if it does this, it has to either 1) ignore the 800x600 to maintain the arbitrary size of your image in inches or 2) change the arbitrary size to match your new 800x600, 72 ppi image (yielding a size of 11.11"x8.33"). Option 1 would give weird results. Option 2 shouldn't affect you in any way, unless your print software uses that size in inches - mine does. That's the only use I've seen for the image size in inches, but at that point it makes sense, since you're talking about certain sized paper and prints, and inches do matter, not pixels.
Sorry for being so long winded - I've never thought it out this much, so I may be a little off base somewhere.
If you choose 800 x 20 it's going to change your image. keep your original image aspect locked when changing your resolution. Iif the longer side is 800 then the shorter side will automatically calculate that for you. I hope this helps you with resolution problems with pixels.
Jeffrey, it wasn't a question of calculating the short side of the image when leaving the long side at 800 pixels. I didn't mean I'd size an image 800x20 pixels. I was simply using the 20 as an example of a pixel-per-inch reading that produces poor quality images when viewed on my computer screen, not as an example of the short side of an 800-pixel-wide image.
Hank, thanks for supplying that crucial bit of info (to me at least). I'll continue setting resolution at 72 ppi for my online images, which is what I had been using most often. What ppi others use is the information I was looking for, since it's clear I don't understand why image ppi is an unimportant consideration for computer screen viewing.
But if you admit that ppi IS unimportant, Steve, does it really matter what others are using?
I'm actually really curious to see what your software reports for image size in pixels, and inches, when you do the same re-sizing at various ppi. I'll probably try it on my own as well.
Steve, ppi/dpi has no reflection on image resolution, none at all - resolution is defined as the number of pixels in the image...that is, the height x width in pixels. The height and width in pixels are the only measurements that the computer uses when displaying an image on the screen.
The size of the image displayed on the screen is determined by the screen resolution you set on the computer, for example my LCD is set to 1280 x 1024. If I view an image sized at 800 x 600 pixels at 100%, it will fill about 3/4 of the screen. The computer is displaying each pixel in the image as one pixel on the screen. If I had sized the same image at 2520 x 2048 pixels and viewed it at 100%, I would only be able to see half of the image on my screen.
Looking in photoshop at the image sizing dialog, the pixel dimensions for an image are in one 'section' that only includes width and height. The other section is document size that refers to the physical dimensions when an image is printed which has width, height and dpi.
Note that changing pixel dimensions will change the document size for print and changing the document size will change the pixel dimensions. So, changing the dpi has no effect on the pixel diminsions nor how the image is displayed on screen - it only changes the physical size when you print. That is, it has no impact on the resolution of the image displayed on the screen.
To summarize, when viewing an image on a screen, the resolution does not make a rat's a** bit of difference! The screen is built with so many pixels per inch (or cm) and the saved image will only cover the number of pixels in its dimensions.
The only time I have ever encountered anything to do with the resolution setting is in Photoshop. If you have an image at 72 dpi, then Photoshop will print it at a size calculated from the resolution. Thus, an image which is 600x800 pixels (dots) at 72 dpi will print as 8.33 x 11.11 inches while at 300 dpi it will print as 2.00 x 2.67 inches. Every other program that I have used ignores the resolution and lets one just specify the overall size. The printere driver then corrects for the resolution.
David, I didn't "admit" that ppi is unimportant. I'm just told it's unimportant by people more technically savvy than myself, and until Mark Wilson led me by the nose, I didn't understand why you all are saying that.
Mark, thanks for that explanation. You detailed things that others already had, but then you went a couple steps further, and that helped a lot. I went into CS2 and looked at the boxes you described, manipulating the image in the ways you mentioned. Now I understand.
Steve, an apology from me are in order. I have reread my reply and am not certain where the idea that you admitted ppi was unimportant came from . However, if you interpreted the post in that manner, then I must have written something that implied that.
If memory serves me, Photoshop was first written back in the 1980's before there was a real Windows. It was designed for photo journalists. I suspect that printer drivers at that time, or at least the drivers which the authors of Photoshop wrote, did not interpolate or extrapolate pixels to fit the size of an image to be printed. Even though Photoshop was originally written for the Mac, the DOS version required its own printer drivers. Consequently, the specification of ppi is a legacy from that time period when the user had to specify the printer resolution along with the number of pixels in each dimension of the image to determine size. Remember, Photoshop was designed for printing, not displaying an image on the web.
Given that the resolution specification is a legacy number, I wish we could have broken the fingers or keyboard of whoever started the myth that one needed to specify 72 ppi when displaying an image on a screen. I still see that specified on a number of sites. The resolution is only used by Photoshop when printing.
For that matter, I am not certain but wonder if there is any other image software which prints using resolution and pixel dimensions instead of size in inches or cm. If anyone knows of some, please let us know.
Mark's explanation is thorough. 72 pixel per inch is the result of a historical legacy to the printing world where 72 points equals one inch. Hence that is primarily a print parameter without any purpose for normal computer monitor display. Browsers normally display based on total pixel dimensions while ignoring that "pixels density for a given distance" paramter.
Like Steve, I set that number in Photoshop to 96 ppi simply because when I work in Photoshop that will tend to approximately display the ruler bar alongside the image window so one screen inch is one print inch. Of course simple digital cameras use the default 72 ppi value so I need to bother changing my files to 96 ppi.
The 96 ppi is an old Windows default due to the approximate typical CRT monitor RGB phosphor dot pitches that a Windows Control Panel Display number of pixels screen setting would be set for. If a Windows monitor with an RGB phosphor dot pitch of about 0.25mm is set up so its selected Display screen setting is approximately using one Windows pixel for one monitor phospor dot, then setting image for 96 ppi will display a one inch image on the screen about one inch long. Unfortunately for we fine art photographers, many printers are set for about 300 print pixels per inch which is three times the density of a typical monitor dot pitch. Hence the difficulty evaluating print resolution on a monitor. ...David
Discussion
19 repliesThanks,
Jim
I would size the image to 800 pixels on the long side which should fit well on practically all modern monitors.
Guy
The question remains, however. So let's talk ppi, not dpi, since we're not talking about print. Help me out here. If I size a horizontal to 800 pixels across, what ppi resolution should I choose, and why? While things have been working just fine the way I've been doing it, I'd rather know the ins and outs than not know.
And so it really doesn't matter whether I choose 20 ppi or 200 ppi at 800 pixels across when looking at a photo on my monitor? If true, that's at least counterintuitive, and sounds just wrong. How can it not matter how many pixels per inch I tell the image to be at 800 pixels across? Or did I misunderstand Darren's and Guy's explanation.
I mean, telling someone to size an image to 800 pixels on the long side without adding which ppi setting is most appropriate for computer screen viewing seems a bit like asking someone to calculate the square footage of a floor with only one of the two required measurements.
(AS an aside, monitors do have a native dpi, but this refers to the absolute maximum resolution you can set the monitor to - so that every physical pixel is used as a pixel in the OS. At smaller resolutions, multiple physical pixels are used for each software pixel.)
It can't be zero, but otherwise it pretty much doesn't matter.
Well, I'll just keep doing what I'm doing since it seems to work fine for me. A person doesn't have to understand EVERYTHING to get through life.
My best guess, though, is that it's using the scale/ruler that's built in to Photoshop. My pictures stright out of camera show up as 14.4" x 10.8" (I think) which is completely arbitrary based on 5 MPixels and a completely arbitrary choice by Canon to encode 180 ppi. Note that Canon could have chosen any ppi to encode, and Photoshop would just adjust the ruler size of my image to compensate. (I.e. if they had chosen 90, my photo would seem to be 28.8"x21.6" in Photoshop.)
Now if this scale is being used, and you set a ppi, it could be stretching/shrinking you image in weird ways. However, if it does this, it has to either 1) ignore the 800x600 to maintain the arbitrary size of your image in inches or 2) change the arbitrary size to match your new 800x600, 72 ppi image (yielding a size of 11.11"x8.33"). Option 1 would give weird results. Option 2 shouldn't affect you in any way, unless your print software uses that size in inches - mine does. That's the only use I've seen for the image size in inches, but at that point it makes sense, since you're talking about certain sized paper and prints, and inches do matter, not pixels.
Sorry for being so long winded - I've never thought it out this much, so I may be a little off base somewhere.
Cheers Mate!
Hank, thanks for supplying that crucial bit of info (to me at least). I'll continue setting resolution at 72 ppi for my online images, which is what I had been using most often. What ppi others use is the information I was looking for, since it's clear I don't understand why image ppi is an unimportant consideration for computer screen viewing.
I'm actually really curious to see what your software reports for image size in pixels, and inches, when you do the same re-sizing at various ppi. I'll probably try it on my own as well.
The size of the image displayed on the screen is determined by the screen resolution you set on the computer, for example my LCD is set to 1280 x 1024. If I view an image sized at 800 x 600 pixels at 100%, it will fill about 3/4 of the screen. The computer is displaying each pixel in the image as one pixel on the screen. If I had sized the same image at 2520 x 2048 pixels and viewed it at 100%, I would only be able to see half of the image on my screen.
Looking in photoshop at the image sizing dialog, the pixel dimensions for an image are in one 'section' that only includes width and height. The other section is document size that refers to the physical dimensions when an image is printed which has width, height and dpi.
Note that changing pixel dimensions will change the document size for print and changing the document size will change the pixel dimensions. So, changing the dpi has no effect on the pixel diminsions nor how the image is displayed on screen - it only changes the physical size when you print. That is, it has no impact on the resolution of the image displayed on the screen.
Hope that makes sense.
To summarize, when viewing an image on a screen, the resolution does not make a rat's a** bit of difference! The screen is built with so many pixels per inch (or cm) and the saved image will only cover the number of pixels in its dimensions.
The only time I have ever encountered anything to do with the resolution setting is in Photoshop. If you have an image at 72 dpi, then Photoshop will print it at a size calculated from the resolution. Thus, an image which is 600x800 pixels (dots) at 72 dpi will print as 8.33 x 11.11 inches while at 300 dpi it will print as 2.00 x 2.67 inches. Every other program that I have used ignores the resolution and lets one just specify the overall size. The printere driver then corrects for the resolution.
Mark, thanks for that explanation. You detailed things that others already had, but then you went a couple steps further, and that helped a lot. I went into CS2 and looked at the boxes you described, manipulating the image in the ways you mentioned. Now I understand.
Jim
If memory serves me, Photoshop was first written back in the 1980's before there was a real Windows. It was designed for photo journalists. I suspect that printer drivers at that time, or at least the drivers which the authors of Photoshop wrote, did not interpolate or extrapolate pixels to fit the size of an image to be printed. Even though Photoshop was originally written for the Mac, the DOS version required its own printer drivers. Consequently, the specification of ppi is a legacy from that time period when the user had to specify the printer resolution along with the number of pixels in each dimension of the image to determine size. Remember, Photoshop was designed for printing, not displaying an image on the web.
Given that the resolution specification is a legacy number, I wish we could have broken the fingers or keyboard of whoever started the myth that one needed to specify 72 ppi when displaying an image on a screen. I still see that specified on a number of sites. The resolution is only used by Photoshop when printing.
For that matter, I am not certain but wonder if there is any other image software which prints using resolution and pixel dimensions instead of size in inches or cm. If anyone knows of some, please let us know.
Like Steve, I set that number in Photoshop to 96 ppi simply because when I work in Photoshop that will tend to approximately display the ruler bar alongside the image window so one screen inch is one print inch. Of course simple digital cameras use the default 72 ppi value so I need to bother changing my files to 96 ppi.
The 96 ppi is an old Windows default due to the approximate typical CRT monitor RGB phosphor dot pitches that a Windows Control Panel Display number of pixels screen setting would be set for. If a Windows monitor with an RGB phosphor dot pitch of about 0.25mm is set up so its selected Display screen setting is approximately using one Windows pixel for one monitor phospor dot, then setting image for 96 ppi will display a one inch image on the screen about one inch long. Unfortunately for we fine art photographers, many printers are set for about 300 print pixels per inch which is three times the density of a typical monitor dot pitch. Hence the difficulty evaluating print resolution on a monitor. ...David