300dpi

[Trendssoul]

I'm sure I'm asking a simple question
how do i do my photoshop work as 300 dpi image jpg
thanks 

[Ged_Traynor · Accepted solution]

@Trendssoul unless you're going to print your images, there's no need to change the DPI, if you do want to change it you can do that from the Image > Image Size menu

https://www.adobe.com/uk/creativecloud/photography/discover/dots-per-inch-dpi-resolution.html

[jane-e · Accepted solution]

I hadn't seen that link before, @Ged_Traynor , but I like that it first correctly defines DPI and only later explains the difference between PPI and DPI!

What does DPI stand for?

DPI stands for Dots per Inch, referring to the number of ink droplets a printer will produce per inch while printing an image. The more dots of ink per inch the picture has, the more detail you will see when printed.

How does DPI differ from PPI?

PPI (Pixels per Inch) refers to the number of pixels that make up every inch of a digital image. It’s used to describe image resolution on a screen, rather than in print. DPI, meanwhile, refers to number of dots in every inch and is generally used for print purposes.

Jane

[davescm · Accepted solution]

Except that some of the information in that article is wrong /misleading.

Pixels per inch ppi is used for printing. An Epson inkjet for example may print an image at 300 pixels per inch. However those pixels are themselves made up of dots and those could could be laid down on the paper at 2880 x 1440 dots per inch or 1440 x 720 dots per inch. So less dots per inch but the same number  (300) of pixels per inch.

If you are making images for screen ppi is irrelevant - the screen on which it is displayed will display it at whatever density that particular screen uses. All that matters is the pixel dimensions (e.g 1920 x 1080 pixels). When you send an image to print then you use ppi (pixels per inch) so the printer (or print driver) can calculate what size to make the image on the paper.

Dave

[Zesty_wanderlust15A7]

Re. "When you send an image to print then you use ppi so the printer (or print driver) can calculate what size to make the image on the paper."

If that is true, I think it's still confusing.

What would be an example of using it properly?

For example, do you somehow state the "true ppi" in that metatag, so the printer knows how to calculate from that, or do you specify a ppi that you want it to become, etc.?

[D Fosse]

Functionally, this is very simple and not confusing at all:

An image pixel can be printed with any number of ink dots.

So the image is pixels per inch, the print is dots per inch.

They are connected by the physical measurement, the inch, but not the same:

pixels -> inch <- ink dots

Pretty simple.

[Zesty_wanderlust15A7]

That part is simple, but you don't answer my question.

We usually hear the ppi field has no importance for printing; it's the pixels that matter. That is easy to understand for me, and what I have always agreed with (I did reserve a place in my mind where some printer might use this info, as so many seem unware or confused by this.).

Dave seems to suggest we do have to use this field wisely when printing?  Then show me an example.

Like, my pic is 1800 x 1200 px and I want it printed at [size], so seeing my printer is [??] dpi, I set ppi at [??].

I may be misunderstandng Dave, but if it wasn't confusing, I wouldn't.

If this was required, I would suspect PS would have a field where you could provide the dpi of the target printer, so PS can recalculate the ppi and spare you the math.

[D Fosse]

Setting a ppi number defines a physical print size. Without a ppi number, the size would be undefined.

It doesn't really matter where the actual calculation is performed. You need a print size, and the ppi number gives you that.

[Zesty_wanderlust15A7]

So give me an example...

You're basically saying that if I print a 1800 x 1200 px pic that has the field at 10 ppi, a quality print at the desired/expected size would fail. It doesn't, AFAIK. Maybe things have changed since I last printed "in the previous century"... 😉

We see over and over that knowledgeable people are saying or correcting others that this field doesn't matter, it's pixel count that matters. I adhere to that until I see an explanation that makes sense. Again, I don't exlude some people have made software that makes decisions based on what is in this field.

If printers would too, I think we would see tons more topics from people getting terrible print results cos their ppi was on, say, 72.

-

What might be related to what Dave is saying, is that I know some perfectionists advise to make the exact amount of pixels for your printer — don't make it recalculate things.

Print Driver Upsampling or AI Gigapixel? (luminous-landscape.com)

-

Maybe this is correct, and why it doesn't matter to me. Inches are strange to me and I never use them.

Pixels-per-inch or Dots-per-inch

http://faczentech.blogspot.com/2015/04/exporting-images-from-lightroom.html

"This comes up OVER and OVER and OVER again and people do not understand it. The ppi box is only useful to people who specify their image sizes in INCHES and not in pixels. If you tell LR (or PS) that you want a picture to be 10 inches wide and 300 ppi, that means you are telling it to give you a 3000 pixel wide image. If you want you can do that, but you could also tell it you want to print a 100 inch wide image at 30 ppi and you’ll get EXACTLY THE SAME IMAGE. Or you could just tell it to give you a 3000 pixel wide image and it doesn’t matter what you put in the ppi box!"

[D Fosse]

You're basically saying that if I print a 1800 x 1200 px pic that has the field at 10 ppi, a quality print at the desired/expected size would fail.

By @Zesty_wanderlust15A7

No, I'm saying it would be extremely big. It would be just fine looked at from across the street.

In practice, you often tell the printer driver to override this, by setting size to fit media instead of 100%. Then the printer driver obviously recalculates - effectively replacing the incoming ppi number with a different one. The same will happen in InDesign where you will soon get used to "actual ppi" versus "effective ppi".

All in all, the importance of the ppi number is overrated. It has nothing to do with actual image data.

[davescm]

Hi

Let me see if I can explain my previous post better.

1. In way of explanation for those people from countries that don't uses inches, 1 inch = 2.54 cm.

2. If you are making images purely for viewing on screens then ppi (which is metadata i.e. a value stored alongside the image) is totally irrelevant. All that matters is the size of the image in pixels. So let's say we have a 6000 x 4000 pixel image. Different screens will display that image at different sizes based on the physical size of the screen and how many physical screen pixels make up those screens. A 24 inch 4K screen will display the same image using the same number of pixels at a smaller physical size than a 48 inch 4K screen. The ppi data is ignored so you could make that value 1 ppi or 1000 ppi it will make no difference on the screen.

3. For printing, as stated by D Fosse, dpi and ppi are not necessarily the same value. Think of it simply -  pixels are the smallest unit of picture information that make up a rasterised image. So our image above has 6000 x 4000 pixels. The printer however can often print those pixels using even smaller dots. So a group of dots is put on the paper for each image pixel. Therefore dots per inch (dpi) can be higher than pixels per inch (ppi). You will not see a control to enter dots per inch (dpi) in an image editor such as Photoshop, at least not one that makes proper use of the terms. You may see a way to change dpi inside the printer driver but it is often labelled differently anyway, e.g. an Epson inkjet driver has a quality control which is actually setting the dots per inch value, it is just not labelled as that.
What you do have in Photoshop is a value for how many pixels should be used to make 1 inch (or 2.54 cm) of printed output. This is the pixels per inch (ppi) value. If such a value was not sent to the printer then the printer would have no way of calculating how big the physical print should be.

An example :

Our 6000 x 4000 image could be printed at 300 pixels per inch. That will print 20 inches x 13.3 inches ( 50.8 cm x 33.9cm).

We could also print the same image at 100 pixels per inch, without any resampling, so it still contains 6000 x 4000 pixels. This time it would print 60 inches x 40 inches which is much larger. But the larger print has no more picture information than the smaller print. 

In addition, a bit of trigonometry tells us that the first, smaller, print viewed from 22.9 inches will look identical in every way to the second, larger, print viewed from 68.7 inches away. That is why we do not need massive pixel counts in large images viewed from a distance.

Of course we can resample an image so that the larger print could be printed at 300ppi. That would then require 18,000 x 12,000 pixels and resampling has to 'invent' those extra 192 million pixels based on the known image pixels of which there were 24 million. It cannot add extra image detail, it can only make the additional pixels up based on the existing picture information. There are various algorithms to do this and all introduce artifacts. The better AI based algorithms can do a good job, but even they are still only making up the missing information. So why resample at all? In some circumstances it may be better to make up those intermediate pixels than to see the pixel structure when viewing the larger image from a close distance. That balance between introducing artifacts and the possibility of seeing pixels when viewed close is an artistic choice.

I hope this helps explain my previous answer

Dave

[TheDigitalDog]

And to add: the PPI (DPI) doesn't necessarily work out to a 1:1 placement onto a printer. An Epson printer may actually produce 2880 DPI, but you would never need to use 2880 pixels for each inch or, for that matter, even 300 PPI (or if you must, 'DPI') for each inch of output as outlined here:
https://www.digitalphotopro.com/technique/photography-workflow/the-right-resolution/

[davescm]

@TheDigitalDog  Exactly - dpi and ppi are two seperate things which many articles, including Adobe the one linked earlier, unfortunately confuse.

Dave

[Zesty_wanderlust15A7]

Great explanation that will serve others well, Dave, thanks!

Respectfully, for 96% it again explains what I already knew, 3% how I used to think (either wrongly or correctly), so that leaves mostly the trigonometry I was not fresh on 😉 I had even added to reasons for resampling in the Luminous Landscape link (reasons you don't mention, but people like Schewe do).

What I want to hear is that you must use this field when printing (which you guys do seem to do, which is what I used to think in the past, but now is "new" to me after seeing so many say it's pixel dimensions that matter, making sense to me).

Also: what would prove that? Any print set at a wildly different ppi?

We've all seen at least the titles of thousands of video tuts. If this field was so crucial, I'm saying there would be many dozens of these videos telling us, "I accidentally (or for demonstration purposes) defined 30 ppi for this photo, and look how it destroyed my print quality!" I've never noticed such demo, and I also restate there would be tons more topics of people screwing up their printing like that. Maybe I'm just not noticing these vids because I don't have a printer anymore, but I doubt that. The topics I have seen more often are from people who don't realize you can simply change the ppi field w/o resampling.

I did have a sublimation dye printer some 10 years ago and sent photos to printing services. The quality was always perfect, but I had probably set ppi to 300. But at the moment, I'm still convinced there is some way to escape the importance of that field for printing too, maybe depending on a choice one makes in the printer dialog and how I always did it. If I had a printer, I would print one of these "300 ppi" photos as 30 ppi and see what happens.

So as final questions...

(1) From what ppi number do you claim I will definitely see a (much) less optimal print? (let's say we are talking the pixel dimensions for handheld photos where, AFAIK, ppi would normally be set to 300). Are you saying 30 ppi or 3000 ppi will produce garbage, even if I state the usual size of the print I want?

(2) And are you sure of that, or do you think there is some way around it, depending what you define in the printing dialog? If this possibility exists, it should be stated that ppi when printing does not matter if [conditions]. It would also make we are both correct 😉

I would be happy to see me make a bad print, as then I will finally have learned. ATM, I'm still convinced I can make the same quality print somehow with that field set to whatever — but the lack of testing and printing experience may prove me wrong... At least I now have a goal to test this somewhere when I can 🙂

[davescm]

@Zesty_wanderlust15A7 

I would advise, wherever possible do not resample. Resampling up (or down) produces artifacts which may, or may not, be worse than the effect you are trying to get without resampling.

So for our previous 6000 x 4000 pixel example it will print at 20 inches by 13.8 inches at 300ppi.

But what if you wanted a 10 inch wide print. Changing photoshops image size with resampling unchecked will give a size of 10 inches x 6.7 inches at 600ppi. No picture information changed, no pixels added no pixels taken away.

There is an argument that says a print driver has an internal resolution (Canon inkjets at 300/600ppi and Epson at 360/720ppi) and that the printer driver will itself resample the image internally if other resolutions are sent to it. I have in the past tested this on Epson by using specially created fine line graphical test images at 359/360/361 ppi and I did confirm some resampling artifacts at 359 and 361. However, on real world photographic images I could see no difference. So for practical purposes I ignore this. If it does concern you you can of course resample in Photoshop to multiples of that native resolution where you can control the resampling method and therefore what artifacts are visible.

If you set ppi to a different value with resampling unchecked, all that changes is the physical size of the print. It gets larger with lower ppi and smaller with higher ppi values.

However if you check resample and alter the ppi then additional pixels are added for higher ppi (via interpolation algorithms as discussed earlier) or pixel information is discarded for lower ppi values.

What ppi should be used as a minimum? It all depends on the viewing distance from the print.

There is a formula which is ppi required = 6878/Viewing distance in inches

That formula is not plucked out of the air. It is based on our eyes and a bit of trigonometry.

A good human eye can resolve 60 line pairs per degree i.e. pairs of black and white lines.  So in half a degree we would have 60 single lines.

Simple trigonometry means that the width containing those 60 lines can be calculated by:
               Width of 60 lines = Viewing distance x tan(0.5°)

Once we know the width for 60 lines (or pixels) we can calculate how many lines per inch can be seen by using 60/Width of 60 lines.

So putting those together gives us

60/(Viewing distance x tan(0.5°))

= 60/(Viewing distance x 0.0087269)

= 2/(Viewing distance x 0.000291)    

= 1/(Viewing distance x .0001454)

= 6878/Viewing distance

Anything above that is wasted as our eyes will not resolve it. Hence the advice to use lower ppi for very large prints that will be viewed at a distance.

Dave

[Zesty_wanderlust15A7]

Thanks again for the effort, yet it again seems to ignore a main question...?

Are you "betting your life" that my 1500 x 2100 px for a 5 x 7 inch photo, printed from Photoshop, assigned 30 ppi instead of 300 ppi (resampling left unchecked), will in any case print visibly worse instead of the expected quality...?

I think I've in the mean time seen equally experienced guys like you be on my side, so one thing we can always be sure of: some seasoned veterans will never get it.

Until I do my own test, I'll remain open to who they will be...

[D Fosse]

The ppi number does not affect the image data in any way. It's just metadata.

As long as you don't use the ppi number to resample. In which case it's not the ppi number; it's the resampling.

Ppi, pixels per inch, is a way to translate pixels to physical size when necessary. Sometimes it's needed, like printing and calculating font sizes; sometimes it's not, like displaying on a screen with a fixed native pixel grid.

You can change ppi and override it at will - the only thing that changes is the physical size.

[Zesty_wanderlust15A7]

Ok, I've now tested it with my laser printer. You don't even have to actually print, but I did.

I can certainly see what you mean now 🙂

In the end I'd say we were both right, but let's say you were the most right. I could also say I was the most right and proved my point, which I think you can't. For me I'm right because your life does NOT depend on picking the correct ppi if you can correct for it. That was my claim and why I pushed that question hard. I could say, "I was right, but I now see what you mean." (and probably did way in the past)

Changing my ppi from 300 to 150 (w/o resampling), you immediately see it wants to print bigger.

OTOH, it's an easy hack to specify 50% in the printing dialog. From that you could somewhat say the number doesn't matter, but what you specify in the dialog, which was an opinion I was familiar with and sympathized with.

On the other other hand, you could say, "If the ppi didn't matter, you wouldn't have to hack for it," and I will give that the most weight 🙂 But is it really a hack? We could go on and on... It's certainly not practical to have to recalculate for it, unless you always need the same output percentage.

Anyway, I hope (for me) from now on the whole thing can be explained in three short paragraphs containing two tests people should do for themselves. These endless threads should not be needed if those tests are done, and I've been guilty myself... Thanks for "pushing me to the test"  😉

[davescm]

@Zesty_wanderlust15A7  said 'Thanks again for the effort, yet it again seems to ignore a main question...?

Are you "betting your life" that my 1500 x 2100 px for a 5 x 7 inch photo, printed from Photoshop, assigned 30 ppi instead of 300 ppi (resampling left unchecked), will in any case print visibly worse instead of the expected quality...?'

A 1500 x 2100 px for a 5 x 7 inch photo assigned 30 ppi instead of 300 ppi becomes a 50 inch x 70 inch photo. Viewed close you will now see those pixels but you don't view such a large image up close. You step back to see it.

The 5 x 7 inch print 300ppi viewed from 22.9 inches will look identical to the 50 x 70 inch print at 30ppi viewed from 229 inches. The information in each pixel has not changed, the number of pixels making up the image has not changed, and each image pixel takes up the same amount of space on the retina of your eye.

D Fosse has used a great picture in the past to demonstrate this point, but I can't find a link to it at present.

Dave

[D Fosse]

Ah, you must be thinking of this one:

It was the most unlikely image in the most unlikely setting I could find at the moment 😄

[davescm]

That's the one Dag. It demonstrates the point perfectly.

Dave

[Zesty_wanderlust15A7]

Thx all. The thing you are all replying to has been explained before, or much I was aware of.

The real point is in my reply before this and after I relearned what effect the ppi field had, and for myself I proved that point.

I will not think or claim again that ppi is "totally unimportant" re. printing, so that knowledge has at least been refreshed in my mind.

I do say (and think I have proven to myself) you can get around it by using the output percentage, so in that sense someone could claim ppi is (also) unimportant re. printing (up to a point — I agree it is a semi stretch).

As the ultimate test I should set 30 ppi instead of 300, then print it at 10%. If there is no difference in quality, I will have again proven the point I was always trying to make.

IMO, if you can get around it this way, nobody should overstate the importance of this field for printing either. Acknowledge that you can get around it and won't lose your life, or at least when keeping the same size or smaller.

-

Don't some people that sell prints use one large psd or photo and simply specify the output percentage (or units) for the required size? At least, they could do that instead of toying with the ppi field, AFAIK — it sure seems easier and it seems to work. Sure, they won't have the ideal sharpening for some of the sizes, etc., but not every print has to be high art.

[D Fosse]

I still think you're overcomplicating and overthinking this.

Pixels per inch.

That's all it is, no more, no less. It means exactly what it says.  It explains itself.

[TheDigitalDog]

I still think you're overcomplicating and overthinking this.

Pixels per inch.

That's all it is, no more, no less. It means exactly what it says.  It explains itself.

By @D Fosse

+1 but....

“There seems to be some perverse human characteristic that likes to make easy things difficult.” -Warren Buffett

[davescm]

You do realise that when you set 10% scale in the print driver you are resampling. Just in the driver not in Photoshop - so with no preview.

Dave