this may sound dumb

[Kathleen]

I'm using the Canon Rebel & editing in Photoshop Cs2. When I open an image, it shows as 72 ppi. image size 48 x 32 When I increase the ppi to 300 it now reads that I can only safely print an image of 11.52 7.68 I don't understand?? I have the check mark taken out of resample image. :confused_1:

[Kevin]

The dpi only comes into play when printing so if you change it in CS2 to work on your image it has no effect.

[Kathleen]

dpi or ppi ? So do I change the ppi to 300 ppi every time I open my image in Photoshop.

[Kevin]

Unless you're printing, I don't think you really need to do anything. All it will do is change the "ruler" at the top. I've never adjusted mine and I've been using PS for years.

When it's time to print, and by no means am I an expert in this area and only recall what I've read elsewhere, you can change the dpi to around 240 or less and still get fantastic results. The higher the number you specify, the smaller the print will be.

[Kathleen]

Yes I only change the ppi when I'm preparing for print. I get confused with the reference of dpi- dots per inch & ppi pixel per inch. You are referring to ppi, am I correct?

[mdephoto]

Kathleen, I am aware from my office right now and can look for more detailed info (if you are interested) but ppi and dpi are not the same thing, even though Adobe seems to insist on using the terms somewhat interchange-ably .... the key thing is that from a monitor and CS perspective you are working with PPI -- your printer deals in DPI but is usually something you don't really need to worry about.

When you bring your image up in CS and it reads 48 by 32 at 72 ppi and you tell it you want it to place the pixels at 300 ppi instead it will change the image to the new size of 11.52 x 7.68 -- as 300 ppi is obvious more dense than 72 ppi. And since you are not resampling the image this is exactly what you would and should expect to happen.

If this is the size you want then all is good. If not, then you have two choices. One choice would be to resample the image to the exact size you want with a specific ppi -- i.e., 300 ppi and 8 x 12, and the other choice is to select the size you want and let the ppi end up where it ends up. My personal preference is the latter -- with the criteria being that the ppi ends up somewhere between 180 and 480. I have found that my printers (an Epson 4000 and HP z3100) work quite well with files that are sent to them with ppi's in this range. You might want to try it with your printers and see if you don't get something similar. I prefer this approach as this way I do not have any interpolation going on in the image and thus CS is not "messing"with the file.

I will also say that I have interpolated the file by approximately 75% up (uprez as they say) on a Canon 5D or 1D MkII file and printed them at 20" x 30" and had no problems with sharpness and clarity when necessary. So, I am not afraid to resample if required.

Hope this helps.

[Kathleen]

Thanks, yes I think I'm beginning to see. So I was correct in saying that ppi & dpi were not one & the same. I hope I didn't step on your toes Kevin. I didn't mean to.

So when you resize a photo, do you first set the ppi to 240-or 300 (preference), then the chosen size of my print, all of this while having the resample checked? Do you also have the Constrain Proportions & Scale Styles selected? When increasing the image size I have heard that selecting Bicubic Smoother as a wise choice. Is this so.

[Kevin]

Glad Mike cleared that up for you. I never pay attention to it, primarily since I'm not printing any of my stuff out. No toes were stepped on this thread either. ;)

[mdephoto]

Kathleen, when you select a specific ppi and a size of a print with resample checked then CS is going to "make" the image conform to what you have defined. I hope you understand that once you have selected "resample" then CS is going to either "create" or "smush" [technical term ;->] pixels to accomplish what you have asked it to do. In other words it is going to use "its best effort to create something out of nothing or reduce something to something to something smaller" to get you what you want. You will typically want "Constrain Proportions and Scale Styles" selected or you will end up with a warped critter, bird, person etc. since not selecting this would allow the width to expand /contract at a different ratio from the height. As I said in my earlier note, I try to avoid having CS create or smush pixels whenever possible as I prefer to keep them as they came from the camera....

It really doesn't matter whether you set ppi or size first as you would normally make all the changes at the same time -- in the same window.

And, finally if you are going to up-size the rule of thumb is to use smoother for upsizing ---- and sharpen for downsizing ---- but I think you will have to look hard to seem much difference from basic in most images for most changes.....

hope this helps...

[Kathleen]

I hope I'm following what you are saying. This is how I've been changing the ppi from 72 to 300. I uncheck resample & enter 300 ppi. I never change the size of the image, unless it is to downsize. I've been doing this for longer than I can remember. Oh my, I hope this is correct, is this what you are saying? One other thought. In preferences you are given the option of setting the screen resolution & print resolution. Since the print resolution is set to 300, is it not a given that the image is 300ppi? Therefore, unless you have need to change the image size you don't even have to go into image size and change it to 300ppi?

I can't thank you enough for all of your help..

[MiriamJ]

I hope I'm following what you are saying. This is how I've been changing the ppi from 72 to 300. I uncheck resample & enter 300 ppi. I never change the size of the image, unless it is to downsize. I've been doing this for longer than I can remember. Oh my, I hope this is correct, is this what you are saying? One other thought. In preferences you are given the option of setting the screen resolution & print resolution. Since the print resolution is set to 300, is it not a given that the image is 300ppi? Therefore, unless you have need to change the image size you don't even have to go into image size and change it to 300ppi?

I can't thank you enough for all of your help..

That sounds right to me, to uncheck resample and enter 300 ppi. This is assuming your printer prints at 300 dpi. Mine prints at 360 dpi, but I use Costco for my prints, and their printer prints at 300 dpi, so I use 300 ppi. Actually works well for me as my photos come into Photoshop already at 300 ppi.

On that print and screen resolution, can you double-check that? I think you might be looking at the new document settings. In that case, those figures would only affect new documents, that is, where you start from scratch with nothing on the page and then add to it.

[mdephoto]

Kathleen, the preferences in Photoshop are a wee bit confusing and it is a shame that Adobe has not stepped up to the plate on this. This setting for print resolution (which really is for PPI and not DPI) is for new images -- it will NOT change an imported image -- as you are seeing on the images that you are importing --- that is why you are having to change your images from 73 ppi to 300 ppi to change your image sizes. Second, the screen resolution setting default of 72 is also outdated and goes back to the monitors of many years ago -- a better setting for today's monitors is around 96 to 100 (I use 100 myself).

In terms of printing DPI, the 300 DPI number came from the publishers desire to print their documents at 150 lines per inch and thru some conversion magic that translated to around 300 DPI and that number has stuck as the magic number every since. Personally I don't think it carries all that much weight in the inkjet world -- especially for our home printing and I challenge anyone to show me a difference between a print from my HP z3100 at 300 DPI and 200 DPI.

The rule of thumb numbers for sending prints to the Espon printers and their 720/1440/2880 DPI ink patterns are fractions of those numbers --- i.e., 180 PPI, 240 PPI, 288 PPI, 360 PPI, 480 PPI. In theory those values are supposed to make it easier for the printer to do its job and convert the PPI math the to the DPI math to lay down the proper ink pattern. BUT, the printer manufacturers know that not everything is going to come to them in such a neat package so they built some pretty good processing capability to handle about anything and thus they can do some conversion on the fly. Good thing to or the would not be able to handle the often requested 300 PPI <grin>.

Now, all that being said -- Jeff Schewe [a Canon Guru, Photoshop Alpha Tester, Epson Guru, long time commercial photographer, etc.] has said something that I fully embrace .... "However, properly sharpening for your image's NATIVE resolution trumps setting the image PPI. If size is critical, re-size without re-sampling and let the pixels per inch fall where they may." I would add that this PPI needs to be at least 180 PPI and anything above 480 PPI is probably overkill. And, if it is not clear native resolution is what comes out of your camera with no up-sampling or down-sampling. Now, I realize that is not always possible for you to get what you want but if you want the optimum image quality (IQ) this is what I believe is necessary.

The key here being when you upsample you are introducing pixels that were never in the image that the camera saw. And when you downsample you are taking away pixels that the camera captured. Obviously neither of these are helping the IQ.

To address Miriam's point, my points are pretty much addressing ink jet printers and have limited application to other printers. If you are preparing images for a specific printer or service it is always best to ask them how they want them - or tell then if they are doing the work for you. At a minimum What color space / profile, what PPI, and what size (as you have seen a PPI always has to go with a size) and what format (jpg, tif, etc). Sometimes, as in the case of Costco you are controlling the size and format and they will tell you the profile of the printers they are using so that you can be sure that the colors you get back will be the ones you submitted. But, hey this is a whole different topic.......


Sorry for this being so long...

[MiriamJ]

Mike,

Your comment: "However, properly sharpening for your image's NATIVE resolution trumps setting the image PPI. confused me a little. Are you using sharpening interchangably with resizing?

It's also interesting that the Canon native resolution is 72 dpi, which, to me, doesn't sound useful for any kind of printing. I'm wondering if Canon expects most shots to be viewed over the internet, or at least over a monitor or digital display, where Nikon is thinking in terms of printing, hence the 300 dpi output.

[mdephoto]

Miriam, I am not using resizing and and sharpening interchangeably and I am sorry if I gave you that impression. What I was saying was that a native resolution image that is correctly sharpened is going to look better in terms of image quality than an image that has been resampled and then sharpened --when pushed to the extremes. I need to add that last qualifier since if you are talking about making a 5 x 7 inch print then you are probably not going to notice a difference at all and this whole conversation is moot. I print out many of my images at 20" by 30" and get real concerned about IQ and sharpness -- you may not have the same concerns. It really depends on what you are going to print. I know that I don't worry about this much at all if all I am doing is preparing an image for the web --- no one can tell what you have done in terms of sampling (within reason) if it is going to be an 800 x 800 pixel image at 72-100 ppi. <very big grin>

Now, in terms of Canon and Nikon defaults --- remember that DPI is nothing without the corresponding sizes, so the numbers you mentioned are not the total indicator of native resolution ------ 300 ppi and an image size of 8" x 10" is the same as 72 ppi and an image size of 33 x 41. So, just having one of those two factors is never enough. If you want to pick just one thing to just native resolution then you need to look at the total file (or at lest that is what Canon calls it) size --- "3888 by 2592" pixels as for the Canon 40D large fine jpg. That is the file size --- the image size would depend on whether you picked 72 ppi or 100 ppi or 300 ppi.

Now why one picked 72 and one picked 300 beats me. While the Canon one might sound good for sending images over the web, I am never too happy when someone sends me one of their images from their new 7 megapixel camera and it comes in at 72 ppi and so big it takes me 30 seconds to scroll from one end to the other --- the sender should have downsized it to about 800 x 800 pixels anyway (to get it to a smaller physical screen size and to reduce the size of the file). In this case, maybe Nikon has the better idea. But then if you don't downsize that file to a more reasonable ppi, you still send out a very large file and it takes up way too much bandwidth even if it is a more reasonable size for the screen.

Hope this helps clear up the confusion ... or, did I make it worse??

[MiriamJ]

Miriam, I am not using resizing and and sharpening interchangeably and I am sorry if I gave you that impression.

No problem. :)

What I was saying was that a native resolution image that is correctly sharpened is going to look better in terms of image quality than an image that has been resampled and then sharpened --when pushed to the extremes. I need to add that last qualifier since if you are talking about making a 5 x 7 inch print then you are probably not going to notice a difference at all and this whole conversation is moot. I print out many of my images at 20" by 30" and get real concerned about IQ and sharpness -- you may not have the same concerns. It really depends on what you are going to print. I know that I don't worry about this much at all if all I am doing is preparing an image for the web --- no one can tell what you have done in terms of sampling (within reason) if it is going to be an 800 x 800 pixel image at 72-100 ppi. <very big grin>

Right! The point was the loss of quality due to resampling. Sure, smaller prints, internet, just resize, don't worry about it.

Now, in terms of Canon and Nikon defaults --- remember that DPI is nothing without the corresponding sizes, so the numbers you mentioned are not the total indicator of native resolution ------ 300 ppi and an image size of 8" x 10" is the same as 72 ppi and an image size of 33 x 41. So, just having one of those two factors is never enough. If you want to pick just one thing to just native resolution then you need to look at the total file (or at lest that is what Canon calls it) size --- "3888 by 2592" pixels as for the Canon 40D large fine jpg. That is the file size --- the image size would depend on whether you picked 72 ppi or 100 ppi or 300 ppi.

Now why one picked 72 and one picked 300 beats me. While the Canon one might sound good for sending images over the web, I am never too happy when someone sends me one of their images from their new 7 megapixel camera and it comes in at 72 ppi and so big it takes me 30 seconds to scroll from one end to the other --- the sender should have downsized it to about 800 x 800 pixels anyway (to get it to a smaller physical screen size and to reduce the size of the file). In this case, maybe Nikon has the better idea. But then if you don't downsize that file to a more reasonable ppi, you still send out a very large file and it takes up way too much bandwidth even if it is a more reasonable size for the screen.


I ignore ppi when setting up for web. It'll display at whatever the viewers settings are anyways. But I do try to keep the pixel count reasonable.

Hope this helps clear up the confusion ... or, did I make it worse??

No, it all makes sense. :) Thanks!

[Paul S]

It's simple mathematics. Your image is 3456 pixels by 2304 pixels. If you display that with 72 pixels per inch, the size is 48x32 (3456/72=48). If you display it at 300 pixels per inch, the size is 11.52x7.68 (3456/300=11.52).

That's all there is to it. If you want to print at a particular size and resolution which doesn't fit into that equation, you need to change the number of pixels by resampling (that's an option in the image size box in Photoshop).

-Paul

-Paul