# DPI for printing?



## DarqueMist (Jan 16, 2001)

When working on an image in photoshop it seems to want to default to 72ppi, for printing purposes should I increase this to something like 300pi?

Also when looking at the image properties (as shown by right clicking on it in XP) it shows the resolution as horizontal 180dpi and verticle 180dpi. Does this mean the image is 180dpi? would changing the image to 300ppi in photoshop give me better results when printed? Lastly does ppi translate into dpi or is dpi strictly controlled by the camera taking the picture?


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## moper (Feb 14, 2004)

Read thropugh this thread:http://forums.techguy.org/digital-photography-imaging/467380-dpi.html?highlight=dpi+ppi
Explains it all.

Another good article:http://www.steves-digicams.com/techcorner/January_2005.html

moper


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## etaf (Oct 2, 2003)

thats quite a big subject

DPI and PPI are often incorrectly interchanged 
Dots per inch - pixels per inch
a printer may produce a lot of dots to represent one pixel RGB etc.

most imaging programs deal with PPI 
and it doesnt really matter what its set to or reporting when looking at the screen as it will use the screens resolution - which used to be 72PPI hence that default - however, modern monitors display upto around 120 PPI now I think and there used to be a difference between MAC and PC - 72 and 96 cant remember which way round.

the important thing is when printing the image - the PPI tell the printer how many pixels to cluster together in one inch of paper.
300PPI is recognised as the highest quality setting - and so if you look at your image and find out how many pixels it has vertically and horizontally then divide those numbers by 300 that will give you the print size.

however, some printers will prefer and produce an image in exactly the same quality using 240PPI

if the image is large and to be used on a wall and viewed from a distance then I have heard that 180PPI will work

In the past I have put a lot of links in this post on a different forum
http://www.dpforums.com/forum/showthread.php?t=2115


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## DarqueMist (Jan 16, 2001)

etaf said:


> thats quite a big subject
> 
> DPI and PPI are often incorrectly interchanged ...


Thanks etaf, I was trolling the web looking to figure out what kind of quality settings to use when making an image in photoshop that will eventually be printed. What a mistake that was, even sites claiming to offer knowledgable advice seemed to be freely interchanging ppi and dpi which I always assumed were unrelated. You gave me a lot or reading to look at there and it will take me a bit of time. Basically what I took from it so far is that dpi is going to be determined by the printer not by anything I do in photoshop. (I noticed that after changing the 72ppi to 300ppi in a BW pict i was colourizing a part of the 180 dpi shown in the pictures properties remained unchanged, is whats shown there just dependant on the camera? Is 180dpi acceptable for a 5x7" print?)


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## etaf (Oct 2, 2003)

> (I noticed that after changing the 72ppi to 300ppi in a BW pict i was colourizing a part of the 180 dpi shown in the pictures properties remained unchanged, is whats shown there just dependant on the camera? Is 180dpi acceptable for a 5x7" print?)


Could not follow this, sorry

if you are in photoshop try this

Image>
Image Size>
make sure resample is *UN*ticked

now you have the pixels greyed out 
so change the settings to show inches
now change the pixels/inch and you will see the printsize change 
Now is 180PPI {Not DPI) Pixels Per Inch acceptable for a 5x7"
I would say unlikely (I print between 240 & 300 on an inkjet / and my dyesub printer uses 300 ) - But the best test is to try it - I have seen some pretty awful prints that some people seem to think are great quality - so it really will depend on what you find acceptable.

Dont mak eimages B&W in camera - its a very poor way to make B&W - you can do tat and a lot more and make a better job in photoshop


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## DarqueMist (Jan 16, 2001)

etaf said:


> Could not follow this, sorry


Sorry, that 180dpi only shows when I right click on the file and choose properties. Not from within photoshop



etaf said:


> Dont mak eimages B&W in camera - its a very poor way to make B&W - you can do tat and a lot more and make a better job in photoshop


already knew that, I was taking a colour pict of my neice on a beach and making it B/W leaving only her bucket coloured.



etaf said:


> make sure resample is *UNticked*


there's something I was missing ... I assume I should leave the "constrain proportions" checked (yes I know it ends up greyed out after unchecking resample)


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## etaf (Oct 2, 2003)

some cameras will have different PPI set up by default - infact i think you can also alter the settings - but it makes no difference as you can see


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## DarqueMist (Jan 16, 2001)

Thanks for your help etaf you've answered my imediate questions and I've bookmarked your links so I can sit down and read them when I have enough time to take it all in.

[email protected]#@ this is one overwhelming topic


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## buck52 (Mar 9, 2001)

Howdy

DPI only has to do with the print size period... It has nothing to do with scaling, resize/resample...only the final print size

300dpi for printing is like an old wives tale... to the human eye 240dpi looks just as good...

As you said there is a ton to know/learn/understand...

I regularly print 14x11 at 200dpi that look terrific from a 6 megapixel camera

buck


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## slipe (Jun 27, 2000)

> Basically what I took from it so far is that dpi is going to be determined by the printer not by anything I do in photoshop.


There is never a reason to change the PPI except specifically for printing.  You determine the printing PPI in Photoshop but not usually in the "Image Size" dialog box. The printer uses whatever Photoshop sends it and does not determine the PPI on its own.

You can do everything in Photoshop with the crop tool. Select the crop tool and then set your print size in the width and height boxes. Put nothing in the resolution box. Crop the picture. The photo will now print at the size you set in the crop box and use all the pixels you didn't crop off. Whatever was set for the PPI before you cropped is totally immaterial. After the crop you can open the "Image Size" box to see what PPI you ended up with for that print size. *This is the only time the PPI in the resolution box has any meaning whatsoever.* Specifically after you have selected a document size to print.

If it is below about 180 PPI you might want to resample up to 300. But don't just automatically resample as that slightly deteriorates the image. When you crop with a number in the resolution box you automatically resample.

You use the crop tool rather than the Image Size dialog box because the image from your camera isn't usually in the right proportion for a standard print size. You mentioned a 5 X 7. You always have to crop a camera image to get an undistorted 5 X 7. No matter what you do in the Image Size dialog box the print isn't going to be right until you crop it to the right proportions. So you might as well do everything with the crop tool.

As a general rule if you end up with an even number like 180 PPI or 300 PPI for a print you resampled. You should never end up with 180 PPI since that wouldn't be a target you would not aspire to. Nothing wrong with 180 PPI if that is what you ended up at without a resample. But you would end up with a number like 178.427 or 184.223 - not exactly 180. If they feel a resample is required because there aren't enough pixels in the image for a large print size, most people resample to 300 PPI.


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## DarqueMist (Jan 16, 2001)

Slipe, you simplified this down (and offered the easiest solution). By using the crop tool and setting the physical dimensions with that I ended up with 288ppi for the 5x7 ... which if I'm understanding everything else I'm reading should be more than adequate. 
Thank you very much for popping in with your 2 cents worth of info, it proved to be a lot more valuable than that to me.


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## buck52 (Mar 9, 2001)

DPI has nothing to do with PPI ...

DPI is for printing...

PPI is for web/screen display



DarqueMist said:


> By using the crop tool and setting the physical dimensions with that I ended up with *288ppi *for the 5x7


That would be DPI not PPI... 200DPI would work great for a 5x7 image


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## Noyb (May 25, 2005)

Quickly stated  PPI only tells Photoshop how big (in Inches) Photoshop thinks each pixel is.
When you go to Print it, the Printer program will determine the DPI for the physical size you selected.

Its really the overall picture size in Pixels thats important.
For example 
If you have a 1500x2100 pixel picture .. And you choose to print it at a 5x7 inch size ... It will print at 300 DPI.

In Image Size .. you can change the size Parameters as you wish  
and it will NOT change the picture .. as long as you DONT have the Resample Image turned on.
This is a way to make the numbers something thats easy for us simple humans to understand.

Play with Image size (resample turned off) .. Maybe itll help you see whats going on.

For example  
You can choose the Inches size that you wish  and youll see the PPI (DPI) that will result.
The Picture will NOT be changed as long as you dont Resample it.


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## buck52 (Mar 9, 2001)

DPI and PPI are in no way related...


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## DarqueMist (Jan 16, 2001)

buck52 said:


> DPI and PPI are in no way related...


I think I get your point buck. 
ppi determines how the picture is displayed on a monitor
where dpi is determined by the printer and how much information it has available to it to cram into the physical parameters chosen for it


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## buck52 (Mar 9, 2001)

dpi is sent to the printer not determined by it


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## DarqueMist (Jan 16, 2001)

but is determined by how much information is available and its relation to the physical size of the print right?


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## Noyb (May 25, 2005)

You're getting it.
DPI and PPI are not the same thing ... but they can be the same physical size.


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## thecoalman (Mar 6, 2006)

Perhaps this will help, I usually find it does:

This is a 72 DPI image:









This is a 600 DPI image:









They are exactly the same except for the DPI. DPI is irrelevant for display in a browser window because browsers display images at whatever the pixel dimensions are, the images both have the same pixel dimensions so they display at the same size. Right click and save both images and insert them into MS word document (assuming you have MS word) What you'll see is that the DPI is used to scale the images to the paper size. The image on the top will appear larger and the image on the bottom will appear smaller. All DPI does is set a default scale for the image in inches and is only used if the application supports it.

Although changing the DPI alone has no affect on the pixel dimensions of the image one thing to be aware of is changing the DPI and the size in inches will. This will resample your image, so only do that on copies as the original is the best it's going to get.


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## moper (Feb 14, 2004)

One more thing, I'd like to add. Correct me if I am wrong. The DPI setting is also program specific. All it does is tell the printer what size to print the picture, assuming you just click 'Print', and make no other changes. Also can be used as a guide to see how large you can go with an image, if you know your printer produces good looking images at say, 240 DPI, or maybe you want 300 DPI. You can change this at printing time, but then you are resamplying the image. As Slipe pointed out, it is always best to crop your photo to the print size you want.

If I change the DPI setting in Irfanview's Information sheet, Irfanview will print a size, according to what ever number I put in. But, open that same image in Photoshop Elements and it ignores that setting. Instead, it uses the Dpi setting that is set by the camera in the Exif data. My camera, a Canon, always puts 180 DPI in the Exif. Changing the Resolution in the 'Image Size' box in Photoshop Elements actually edits the Exif data, whereas Irfanview must put it somewhere else. Paint Shop Pro uses the Dpi setting altered by Irfanview. Any thoughts on this?

Doing a little more checking, I discovered that Photoshop Elements reads the Resolution from the Exif data, if it exists. But if I change the resolution in Irfanview, untick 'Keep Original Exif Data', while saving, then Photoshop honors the new resolution setting. Pictures from my Olympus camera always showed 144 dpi in the image size box. That's what is in the Exif. Go figure.



moper


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## slipe (Jun 27, 2000)

PPI always refers to pixel density. Unfortunately DPI is still acceptable for pixel density. On photography and graphics discussion boards like this one and for most Photoshop tutorials PPI represents pixel density and DPI represents the dots required to represent those pixels. But there are segments of the graphics community that still use DPI for pixel density.

I have encountered at least a half-dozen posts on various graphics and digital photography boards from people who got requirements for submissions to various periodicals. In every case the photo editor required the photos have a minimum DPI - usually 300 DPI. Never once was the requirement given in PPI. The answer by some of our graphics geeks might be to suggest the periodical get a photo editor that knows something about graphics. Definitely not the right answer if you want to get a photo published.

Ten years ago you never saw PPI. Even very old versions of Photoshop used DPI for pixel density. Unfortunately there isn't a sanctioning authority that can say "as of 29 Feb 01 all references to pixel density will be as PPI."

Pixels do not have a size. They are either 8 or 16 bit references to dimensionless points (for color). There is nothing wrong with thinking in terms of the dots or phosphors required to represent a pixel in terms of size, but pixels technically don't have size.



> dpi is sent to the printer not determined by it


I think you meant to say PPI is sent to the printer - at least from Photoshop. You send the printer a print size and the pixels to use for that print, which is PPI. The printer driver then uses the selected quality and paper plus the printer capability to determine a DPI for the printer. I know of no way to send set a printer DPI from Photoshop.



> Quote:
> Originally Posted by DarqueMist
> By using the crop tool and setting the physical dimensions with that I ended up with 288ppi for the 5x7
> 
> That would be DPI not PPI... 200DPI would work great for a 5x7 image


I think *DarqueMist* got it right. Photoshop sends a PPI to the printer. I agree that 200 PPI will give an excellent print. I have used a loop and think maybe I see some improvement to 240 PPI. But 200 *DPI* on a 2400 X 2400 *DPI* printer is going to be really poor.

*moper* Thanks for the great post. I'm embarrassed I never did your simple experiment rather than go on erroneous assumptions.

All graphics files can have a document size. From this it determines the PPI. I had always assumed that my Nikon used a 300 PPI document size, my Olympus a 144 PPI document size, my Casio used a 72PPI document size etc. And that those were reflected in the Photoshop resolution box. That obviously isn't true. Evidently there doesn't have to be anything in the file about document size and pixel density. If there isn't then Photoshop reverts to the EXIF. If that isn't available it reverts to 72PPI. 72PPI never had any significance with PCs, but Photoshop was originally a Mac program and goes home to Mama. Other programs have picked up the standard.

To expand on your experiment, Photoshop evidently works a little differently than Elements. Say I open an Olympus file in Irfanview and put 300 in the DPI box. Then I "Save as" stripping the EXIF. Photoshop will now read the document size information from the JPG file and show 300 PPI even though the EXIF has been stripped. From your post I assume PSP also reads the information Irfanview has put in the JPG file and is no longer dependent on the EXIF. Elements evidently can't read the document size information you have put in the JPG file.

That Irfanview still uses DPI rather than PPI for pixel density is another example of my earlier premise that it isn't a black and white issue that pixel density is always noted in PPI. Irfanview should switch to the better nomenclature though. DPI can be confusing when it refers to pixel density.


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## moper (Feb 14, 2004)

> Elements evidently cant read the document size information you have put in the JPG file.


No, it works just like you say Photoshop works. If there is an Exif, it always reads that first, regardless of what Irfanview put in there. But, remove the Exif information, then it uses the Irfanview setting.

Why do camera manufacturers use these settings(180, 144, 300) and not allow you to change them?

I was curious about this behaviour, because I read this post where the photographer wanted to change this default setting in the camera. He would take many photos at a car show, then print them out the same day, on site. His system placed each photo in a template before printing. It was set up to use a photo at 180 dpi. It worked fine on his Canon, which defaults to 180 in the exif. But he acquired a second camera, which had a different default setting, and the pictures weren't sized right inside the template. He could manually adjust this, but time was important when printing hundreds of photos. As far as I know, he never did change it. It must be embedded in the firmware of the camera.

moper


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## slipe (Jun 27, 2000)

The default PPI is totally immaterial. I don't know how else I can put it. If you look at the print size for a 72PPI or 180PPI or 300PPI image from a digital camera it is never in a document size you would want to print.

After you crop it to the proper proportions for the print size you are looking for and set the document size you have a PPI that has no relation to the original PPI the camera defaulted to.

I'll try again. Unless you want a 14.222 X 10.667 inch print from a 180 PPI 7Mp image or a 35.556 X 26.667 inch print from a 72 PPI image, the default PPI *has absolutely no significance*.

Edit: Photoshop also ignores the document size and resolution information in the file if the EXIF is available. Odd behavior IMO. And again totally unanticipated. Thanks again for the input.


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## moper (Feb 14, 2004)

I realise that the default camera setting is not important if you are going to crop and edit. All I'm saying is that if you open an image in Elements and click Print, it will print a size determined by the exif resolution setting. This photographer wanted to mass produce the prints directly from the camera. I don't know what software it was, but the problem was that the printing software was interpreting the size differently between the two cameras. Evidently it was using the exif information to size the photos. One camera, they fit in the frame properly, the other they didn't. Here's the post: http://www.dgrin.com/showthread.php?t=36578

moper

moper


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## buck52 (Mar 9, 2001)

Howdy

I hate to admit it but I get a headache just thinking about DPI and PPI...   

I use Photoshop...My camera defaults to 300 resolution in the image display box...I always uncheck resample, the resulting numbers, under document size, are what I print with either of my Epson printers... If I want a specific size ie: 8x10 or 20x30 I use the crop tool with nothing in the resolution box... For a 20x30 I may upsample to increase the dpi/ppi. otherwize what's in the document size box is the exact size that prints...I was under the impression that should be called DPI... If I am wrong, that's OK and I appologize... What I do know is, that the way I do it, produces terrific prints of the exact size I want, first try every time... 

buck


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