Avoiding the confusion DPI and PPI - they are not the same, a guide for editing images and printing

Although sometimes used interchangeably DPI and PPI are not the same thing. A guide for editing images and printing them.
When does it matter - do camera images have a PPI?

The written guide to this is at:

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[Stefan-ocbo]

Thank you for this clear explanation. It sometimes surprises me how PPI and DPI are confused. On the other hand, I had the same problem in the beginning, but luckily I know and understand it correctly now. And of course a happy new year for you and your family.

[tmartin]

Thanks, your written guide was most helpful as I just purchased an Epson 8550. I also appreciate your scientific approach as you investigate camera and printer performance details.

[Charles-Sweeney]

Excellent information, Keith! I always wondered why printers had much higher dots per inch than than the pixels per inch of the image. My mistake was: Thinking a pixel and a dot were the same size! So multiple printer dots are used to print one image pixel. Got it!

[ColzoArt]

Happy new year! This is such a helpful video again, Keith! Shall be sharing this. With some digital painter friends as the same principles apply in terms of DPI / PPI

[cnicolo]

Thank you Keith very interesting. Happy new year 🎊

[frstesiste]

Really good point IMO to try to determine the knowledge level of people to be able to provide help. I run into the problem all the time, both with photo and computers that someone don't understand what they are asking.

[randyb]

Thanks Keith, very helpfull. I recently bought a P5000 and am very happy with the color and B & W that I'm getting from it. Now I am trying to learn about proper sharpening and upscaling. This shoud be a great place to start. Thanks again

[davidduffy]

Amazing info, TLDR aim for 1440dpi like the OG. Your channel is so useful, thanks

[mb-moose]

I'm looking forward to the piano video series😂. Happy new year

[richardparis]

Hi Keith...I jumped from your other video on ET-8550 Borderless Printing and this vid brilliantly explains a few things I've been wondering about. I've also looked at the written guide.
I understand how ppi. and dpi. work in theory but I just want to clarify something. The photos I take with my Nikon are 240 ppi and I usually upsample them to 300 ppi before I edit them in Photoshop - I do fine art photography and do a lot of Colour Grading and other retouching and I have always been happy with the quality at this resolution. 
What I have never really understood until I watched your video is the relationship between the digital image resolution (ppi) and how that relates to print quality.
Question: Am I understanding correctly that bumping up the working 300 ppi. Photoshop image resolution is essentially irrelevant because any beneficial increase in print quality is determined by the printers DPI setting.
Second Question: How do I set the Epson ET-8550 to print at 720 when using Photoshop Manages Printing - I am using the latest version of PS.
Thanks.

[jpdj]

Pixels for resolution, and dots of ink for gradation. I became consciously aware of that late in the digital day. There must be an optimisation problem in there, though, that Keith you are more aware of than I am.
And you may have figured it out already.

If we leave the "per inch" out, I would distinguish 3 scenarios in the frame of an image: (1) we have more pixels than dots, (2) they are equal, (3) we have more dots than pixels.

As you say, the printer will place colours over each other in order to mix towards the colour described in the pixel.
Between pixels and dots at some point we have an alignment issue between pixels and dots (but at a level probably too small for the naked eye).
Also, as dots can be placed over each other, we need to distinguish two things: the amount of dot-coordinates versus the amount of dots of ink placed on those dot coordinates. If a dot in location [x, y] needs only precisely light grey, then that one dot location gets one squirt of light grey. But a dot coordinate that must become greyish yellow may get a grey dot with a yellow dot over it.
In that sense, DPI may be "dot coordinates" per inch.

I know Keith, you know all this better than I do - this is communication: you say something (video) to me, I say a similar thing back in my words and we think we understand each other (or not).

For example, I am inclined to avoid (1), but in smaller prints that's impossible.

The question here is, what software, where, makes the calculations and image analysis needed because of the mismatch. Does it happen in the printer layer? In the printer's print engine?
There must be some image processing involved. And then we should wonder, what impact this has on the image's quality (detail sharpness, gradation, absence of added digital artefacts).

I don't have the answer. It may be trivial.

[JónStefánsson-of]

Hi. If printing an image that is 6496 px x 4640px for example on 5x7 paper that would be 928 ppi. Thats more then needed and if it is more than my printer can handle is it better to downsize it in photoshop or just let the printer software downsize it. I have canon pro 200 and canon professional print and layout.. I usually send all my pixels from photoshop to ppl and do the settings there regardless of if the resolution box in the image size box says if 72 or something else. .the image has its pixels no matter what. I usually upscale in some photo software
Am i doing it wrong?

[shallowman]

Hello keith what printer would you suggest for casual photos, i want to try raw editing thanks.

[thomaseriksson]

Thank you. I recognize parts of this video from your earlier videos. There will be allot of work for me when I start printing. I have 12Mpix and 16 Mpix that I use for wildlife, 36 Mpix and 45 Mpix, that I use for woodland, cameras. I aim to print A2 and I think I need some good AI program for noise reducing, Topaz Labs DeNoise AI, and a good pixel upscaling, Gpixel AI, program from 12 Mpix to 34 Mpix for A2 print.

[dunnymonster]

Indeed Keith, DPI/PPI often gets used interchangeably as if both are essentially describing the same thing. You often hear people say things like, oh the maximum you can print " X " resolution image is 13" x 19" ( or whatever ) just because they believe the amount of pixels per inch must equal the number of dots per inch when printing. Of course you can print a 2MP image 20ft x 14ft should you wish all be it the amount of translational pixel data in the image itself will limit how close you can view the final result. The printer driver cannot create data that wasn't there in the first place no matter how many dots it lays down per inch. Here is where viewing distance is making the defining difference. There is technically no reason you couldn't print a 20ft billboard at 300dpi if you so wished but what would be the point if you can achieve the same visual outcome printing at vastly less, say 20dpi given it will be viewed from 30ft away anyway. I do agree however that as it stands today there is no reason why you should set a specific dpi at all. Just send the maximum image resolution to the printer and let it's driver calculate the DPI based on its own capability. If it chooses 1500dpi then that's fine whether the final print is being viewed very close or far away, I don't think you can have " too many " dots per inch ultimately, unless doing so uses vastly more ink or takes so long to print that it has a negative impact on workflow. This is not to suggest that there shouldn't be some level of consideration when choosing a specific dpi when printing. For example I just leave mine set to 300dpi for everything from 4 x 6" prints to much larger 13" x 19" prints and get satisfactory results. If I were printing vastly larger knowing my prints would be viewed much further away I might be inclined to reduce the DPI but I generally stick to 300dpi as a general rule. I've let my printer choose the DPI of some of my small 4 x 6 prints and it often chooses a crazy high dpi of 1000+ depending on the pixel resolution of my image. I personally can't see any real world difference between a 4 x 6 ( 45MP image ) print at 1000dpi over the same print at 300dpi anyway even close up! This is why I set my print output to 300dpi and leave it. I'd suggest others do the same and stop fretting over the whole dpi/ppi thing. 😋

[centurymodern]

The PPI doesnt matter when viewing on screen, you can make it 1 or a million PPI and the photo on screen will he the same. How is a photo and its relative size to screen measured? Is rhis measured on terms like 1080p or 4k?

[DCockey]

The prevelance of "PPI" being used when there is no associated physical size is both amusing and confusing. What is the meaning of PPI for an image which will be projected to an arbitrary, or shown on monitors/screens of assorted sizes? Of course it is meaningless. The overall number of pixels in each direction is what matters in those instances.

The confusion appears to be embeded. An Adobe web page about PPI says:
"Does higher PPI mean better quality?

Yes, a higher PPI generally correlates with better quality, as the image will have a higher pixel density. However, you’ll also need to take into account the full number of pixels in the image to understand its resolution entirely."

Agghhhh! When I export/save a file without resizing as a JPEG, TIFF, etc the PPI I select has no influence on the resolution. At least the last sentence is a weak attempt to clear thing up.

On the other hand I've discussed this topic with folks who cannot comprehend the idea of resolution without an associated physical size.

[cameraprepper]

So to easier understand, dpi is for an area and ppi is for a line.

[davidmilisock]

This is the only time I've heard the truth in a video about images, they have no physical dimensions until you assign a resolution. It's just simple!

The other BS you hear is that resolution does not matter on the web. Of course resolution matters, some displays are 96 DPI and others are 200 DPI so the same pixel count displays on screens with these specifications at radically different physical sizes.