Photoshop Ninja
Expert Photoshop tips and tricks for designers and photographers since 2005
Image resolution and DPI explained
Image resolution is a very important area to fully understand when using Photoshop, as it dictates the printed output dimensions and quality of your image.
Really printed output dimensions are dictated by DPI (Dots Per Inch), or sometimes referred to as PPI (pixels per inch) – whatever term you use they mean the same thing. This refers to how many pixels get printed in an inch. So, if you have a 600 pixel x 600 pixel image at 300DPI, it will output at 2 inches square. If you change this images DPI to 150, this will mean it will output at 4 inches square. So, as you can see, changing the DPI of an image changes it output size.
However, lowering the DPI too low produces progressively lower output quality. Optimal DPI is dictated by the output medium and size. 300DPI produces high quality output on any medium, but produces large files. I personally use this for anything smaller than A3, unless I need really high quality output. For A3 images I would work to 300-200DPI. For larger items I would use 150dpi, and for really large items like exhibition panels I would use as low as 75-100dpi.
For large format digital prints you can actually get away with amazingly low DPI and still get extremely good quality prints (RIP, printer and operator allowing!), 100DPI is no problem for this kind of print.
Good quality Lytho (or similar) commercial printing really requires you to have your images in the 300-200DPI range.
Screen printing is inherently lower quality than lytho and usually uses a courser screen to print with, so you can get away with going lower than 300DPI with this style of printing.
For home inkjet or laser prints and even digital laser prints you can actually get away with images as low as 150DPI, dont think that because your inkjet printer has an output DPI of 2800 you need your images to be set to this resolution, this just refers to the printed ink density on the page!
Obviously, if you are bringing your Photoshop prepared images into a layout application like Quark or InDesign, you can scale your image to different dimensions – scaling an image larger effectively lowers the actual output DPI, so if you scale our 600×600 pixel 300DPI square image by 200%, you just lowered its actual output DPI to 150DPI.
On the flip side of this, if we where to take the same image, and scale it by 50%, we would end up with an actual output DPI of 600. You may think this is better – it is not! All this actually does is slow down the printing of the document (the RIP has to resize your image), and produce larger jobs to send out to print and archive – this really does you no favours!
When using images in such applications I personally place the image on the page and resize it as required for the design in the DTP application. Once the design is signed off I will then go back and scale the image in Photoshop so that it is sized at 100% in my DTP application. Doing this also allows you to accurately control sharpening of your image.
If you are enlarging an image in your DTP application – again, go to Photoshop and resize the image for all the same reasons above, as well as Photoshops image resize algorithms are fantastic! You also will see how your image quality is degraded and have the ability to combat this in Photoshop, rather than just cross your fingers and hope that no-one notices you resized that image by 250% and its going to look rough – until your client demands a reprint that you have to pay for and get delivered…by tomorrow!
If you want to change the DPI of an image, go to Image Size, tick off the ‘Resample Image’ option, and then type in a new DPI, you will see the image dimensions change to reflect this. Alternatively, if you know the desired output size, you can type this in (with Resample Image unticked) and see what DPI your image will output to.
This information only refers to printed material, image dimensions for web and multimedia usage are purely defined by pixel dimensions and they are traditionally set to 72dpi, although I usually prepare my images at 150DPI if im ever unfortunate enough to have to prepare images for Powerpoint – they will then print fine on an office laser or inkjet printer.
(8 votes, average: 4.50 out of 5)
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Written by Jonny Allbut - freelance graphic designer
Last modified: 19 July, 2005 (08:47) | First published: 19 July, 2005
Filed under Photoshop Top Tips, Techniques - Print 28 Comments »
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Comment by Argy
November 21, 2006 @ 5:35 pm
Very good exlpanations, understood right away!
keep it up!
AC
Comment by basicstate
February 1, 2007 @ 4:34 am
Arghh!
Thanks for the information though.
Just finished my new cards, and it looks like
I’ll have to go back and redo them.
Might as well be now, before I print them.
Comment by Jonny
February 2, 2007 @ 12:46 pm
Well, remember the basics for print:
- 300 dpi
- CMYK colour
… if you stick to those rules you should be ok Basicstate! Hopefully I just saved you a re-print of your business cards!
Always remember to talk to your printer before ANYTHING is printed, they will be able to best advise you about your files and what quality you can expect from the final print job from your files.
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November 16, 2007 @ 9:15 pm
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Comment by Katie
August 20, 2008 @ 5:27 pm
I need confirmation of something I already know but continue to feel unsure about. I am the designer of a magazine so my question pertains to printed materials not on-screen images. The images we print have to be 300 dpi so how do I handle an image that I when open up in Photoshop is 72 pixels/inch (under image size). I know I can actually change the number from 72 to what ever I’d to change it to but how will change the pixels/inch effect the printing? In other words, can I increase the pixels/inch to say 300 in order for the image to print better? Or does the image I receive have to already be 300 pixels/inch?
Comment by admin
August 29, 2008 @ 9:28 am
Keep the pixel dimensions of the image the same by not ticking the ‘resample image’ option in Image size – by changing the DPI you are simply embedding the information in the image for output devices.
If you resize the image (probably larger) you will NOT improve output quality – in-fact you will DECREASE image quality!
Comment by Katrina
May 19, 2009 @ 6:53 pm
hi!
i need help, i am an interior designer, not graphic….so im a bit lost here, i am designing an advertisement for myself, and the magazine that publishes it asked me for the image of 300 dpi, but when i open “new” document in photoshop i dont see the dpi setting, where do i find it? do i initially set the document at 300 dpi or do i do that after i have designed the ad? i hope my question makes sence…
thanks a lot
Comment by Photoshop Ninja
May 20, 2009 @ 5:10 pm
That’s an easy one Katrina – Photoshop refers to this as PPI or Pixels Per Inch which is actually a more accurate description in a way! You may see ‘Pixels Per Centimeter’, just drop the menu down and you will see ‘Pixels Per Inch’.
Comment by Janet Cinelli
June 29, 2009 @ 8:11 pm
When I bring photos into PhotoShop from my camera, Photoshop shows them at 72 DPI. Should I change that setting so they come in at 300 or should I update the photo once it comes in — from 72 to 300. Will doing the latter hurt the image quality?
Comment by Adam
August 9, 2009 @ 10:24 pm
I use Photoshop CS and I have recently been having trouble trying to start off with the right size canvas, I want an 8.5 x 13 inch canvas, and have found that when I set those dimensions the canvas size ends up being dictated by the PPI (set at 300)and will actually turn out much much larger than I need it.
In the past when working in Photoshop I usually started with my canvas size based off of pixels instead of inches, and haven’t had any problems until now, but even when I try doing the math (300*8.5=2550 pixels, etc) I cannot get my canvas size to match the specific dimensions I want in inches.
It doesn’t make sense to me, it seems that when I set my canvas to be started at 8.5 x 13 inches, then that is the size it should be, but it comes out so much larger (at 100% zoom). My assumption is that it is something very obvious that I am just missing or not thinking of for some reason, possibly some setting I made in my preferences a long time ago and forgot about, but I just can’t figure it out.
Comment by Photoshop Ninja
August 11, 2009 @ 1:10 pm
Janet – changing the ‘native’ PPI/DPI of an image will not harm it. However, changing the PPI/DPI when you have the ‘resample image’ box ticked will resize your image – potentially degrading it if it gets larger.
Just un-tick the ‘resample image’ box and you will be fine in the image size options.
Comment by Photoshop Ninja
August 11, 2009 @ 1:17 pm
Adam – my best advice to you is if your are working for print to set up your image at 300ppi/dpi and then set up the dimensions. You should be able to drop down the boxes next to the number fields to change the measurements (to inches in your case).
BEFORE YOU HIT OK, you may find it useful to save a document preset of this. Just hit the button ‘Save preset’, as the presets also set dimension preferences – so if you save a preset with inches and another in pixels, when you select the preset from the drop-down menu at the top of the new image options it will change the measurement increments accordingly, rather than them staying the same, which also may save you some of your woes I hope!
Comment by Brad
September 18, 2009 @ 12:09 am
I am trying to put a powerpoint presentation together that will be projected onto a large screen in an auditorium. My photos have been scanned previously, then printed on paper. Nobody knows where the original photo’s are at. How can I rescan what I have and at what dpi is best for projection’s best quality?
Comment by Photoshop Ninja
September 28, 2009 @ 1:57 pm
Be careful to note that the PPI (or ‘DPI’ – same thing) setting dicates actual output size. So a 1inx1in image at 100dpi would be 100 pixels square, where as a 1inx1in image at 300dpi would be 300 pixels wide and tall… hope that clears it up for you!
Comment by Photoshop Ninja
October 5, 2009 @ 1:55 pm
Humph – that’s a tough one, it’s always tricky when original files get lost! PowerPoint presentations only require fairly low resolution images, but you will probably get best results scanning them in around 600dpi, and reducing down the dimensions of the image with a little sharpening to get the best results.
Comment by Sydney
October 15, 2009 @ 3:17 pm
My HP LaserJet is 600×600 DPI with ImageRet 3600 technology. Is there any advantages to have an image *print* resolution at 600 DPI instead of 300 DIP? My understanding is if an image print resolution is at 300 DPI, then 300 dots(pixels) will fit in 1 inch (lets just talk about horizontal space), then the printer which can produce 600 DPI will print 2 dots for each 1 dot(pixel) of image (not considering image dots below and above or the 8 adjcent dots for simplicity), using halftone or dither to achieve close enough color. So if the image print resolution is at 600 DPI does that mean the printer which can print at 600 DPI will not be able to halftone or dither because every 1 image dot(pixel) will be directly related to 1 printed dot? Taking this further, if an image print resolution is higher (say 1200 DPI) than the printer DPI (600 DPI), will the printer drop the extra image pixels or will it use them to evaluate a more accurate (say, averaging surrounding colors) printed dot/color? Perhaps it is printer specific.
Comment by Photoshop Ninja
October 15, 2009 @ 3:25 pm
Sydney – I respect your attention to detail into getting the very best quality from your printer, I’m a real stickler for quality too! I also understand where you are coming from with your numbers – in theory it all makes sense what you are saying but to be totally honest, I find that 300dpi is more than sufficient (and is used for high-quality commercial print) to get excellent quality results.
The reality of it is that all printers employ different techniques when actually ‘ripping’ the file to print, some do it better than others (especially high-end large format digital printers… you can get away with amazingly low resolution and the rip seems to dither the image really well!)
The quoted DPI of your printer relates directly to the ink density that it lays the droplets down at. I have seen no advantage of going higher, all that seems to happen is it takes longer to send and ‘rip’ the print file.
With a half decent printer, ink and paper you should be fine just sticking to 300dpi.
Comment by tammy
October 22, 2009 @ 4:01 pm
I read all the comments in this thread but am still finding this hard to understand, sorry.
I have an image that I need to use for a printed publication. In Adobe Indesign, the image is shown as having a 300 dpi, but because I increased it’s size on the document, Indesign is showing it as having an effective dpi that is much lower (aound 150, too low to send to the printers).
My client doesn’t have a larger (or higher resolution) version of the image, but they really want to use this particular image.
Can I increase the dpi in photoshop? Will this increase the quality of the image? The client sent me an email suggesting this, but I wasn’t sure that it’s possible.
thanks!
Comment by Photoshop Ninja
October 30, 2009 @ 10:08 am
I’m sad to say that increasing the resolution in Photoshop WILL NOT increase the quality of the image. The quality is as you have it in the original image I’m afraid. Resizing the image in Photoshop will blur it, although you may get a slightly better result than resizing it in InDesign. There are a couple of Photoshop plugins that do a-little better job of scaling images up, but these are of-course commercial ‘paid for’ solutions that I have very little experience of so I can’t really recommend one sorry.
Comment by Andrè
December 10, 2009 @ 5:37 pm
But lets say u make a design in photoshop by dragging different images into one which is 72dpi, and the images have different dpis, this means only they will appear bigger in the 72dpi design when dragged in right? so most of the times u will have to shrink it to fit the design….but when doing this and then sending it to print, lets say the design made in 72dpi is gonna be printed in a3, then it wouldnt be worse quality? as long as the images used has clearity and u dont enlarge them when designing right?
It is always prefereable to have high dpi project from beginning but then the pictures have to be high dpi too otherwise they would appear wery small(72dpi) to get same clarity as the 300dpi images is this right?
lets say you design a project in 300dpi a3, then a good quality picture in 300 dpi would take same space as 4 pictures in 75dpi right? but the 75 dpi pictures could have just as much clarity as the 300dpi picture as long as they where their original small size? and if using 75dpi pictures I could just as well design in a 75dpi photoshop project and get just as good quality? or would always 300dpi project setting give higher print quality?
Also after reading this I noticed some of my finished projects where in 72dpi and I tried settting to 300dpi with resampling off, if I had printed this out again would I get a better quality print?
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December 30, 2009 @ 3:01 pm
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Comment by Photoshop Ninja
January 15, 2010 @ 3:51 pm
To clarify (hopefully!) – when you are working in Photoshop and dragging images from one document to another, dpi has no relevance – think in pure pixels. So you may have one document that’s setup to 10inches x 10inches at 150dpi (1500 x 1500 pixels), and another document that’s setup to 10inches x 10inches at 300dpi (3000 x 3000 pixels). If you drag a layer from the first document (150dpi) into the second document (300dpi), the layer would be exactly half the size in pixel dimensions in relation to the overall document size. You can see that although both images are set to print to 10in x 10in – the first will output to 150dpi and the second will output to 300dpi (that’s where all those extra pixels go… resolution/quality of image!).
On resampling – when chaging the dpi of an image, untick this box. You then will no physically resize the image (unless you really want to do that of-course!).
Comment by Khaliah
February 18, 2010 @ 5:02 pm
I’m having a bit of an issue with some files I have on Photoshop Elements 8.
For a project, I’m told that the finalized pieces need to be 600 ppi. I have no problem with that, and scanned them in at that resolution. I touched them up in Photoshop, and now, each one is around 10 MB or so.
For some reason, they won’t print. Both I and my client attempted printing them, but they won’t print. Are the file sizes too big?
Comment by Photoshop Ninja
March 4, 2010 @ 11:52 pm
Strange – maybe try saving them down in a different format, the size shouldn’t be a problem. TIFF would be worth a try.
Comment by kadie
March 5, 2010 @ 9:46 pm
Hi there,
I am in need of help..I do not speak computer so bare with me:
I am a screen printer and use photoshop to manipulate my images and print transparencies to use as my films. I am working in a printmaking shop that has a Canon MF6550 printer and a HP P2055dn (which we just bought because I thought it would work and it is not). When I go to print to create a halftone (this is how I have done it in the past without problem) I press print, a box appears for me to adjust settings, add crop marks…there is a screen button. I go into screens, adjust the frequency to 20, round dot and print…and no matter what I do it prints the printers default. I called HP and they said it is not their problem. Do you have any suggestions? Thanks KD
Comment by Photoshop Ninja
March 21, 2010 @ 11:08 pm
Hi Kadie – sorry I’m not familiar with the output device, the best I can suggest is a good look on Google and it their support forums/faq’s and documentation… good luck!
Comment by harry
April 22, 2010 @ 1:07 am
Hi, im having some trouble… I have a large image that is 140cm x 300cm and its resolution is 72 pixels/inch but I need the resolution to be 300. When I change the resolution to 300 it changes the size of the image to 31cm x 72cm? How can I change the dpi but retain the large size?
Comment by Photoshop Ninja
April 30, 2010 @ 2:50 pm
It just doesn’t work like that – this is the size it will output at the same quality at 300dpi. If you tick the ‘resample image’ option you will see how your image degrades as Photoshop will have to resize it.