Can someone explain to me example how DPI is relative to monitor size and size it would be when printed

Can someone explain to me example how DPI is relative to monitor size and size it would be when printed.

Say for example I scan a page of book in 300dpi, the image data tells me that the page is roughly 10 inches tall and 7 inches wide. Scan that same page at 600dpi and the image data still says it's roughly 10 inches tall and 7 inches wide.

The thing is, my monitor is 30 inches wide, and the image itself doesn't look stretched out or warped at all. So, by that logic, shouldn't I be able to print the originally 7 inch wide page out onto a 30 inch sheet of paper and have it look fine?

I've done basic google searches and read some info about this, and all I could really come up with is that it has something to do with the relative dpi of the monitor itself and that the computer calculates and fills in the "missing" pixels.

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digitaltrends.com/photography/printing-large-photos-the-right-way-version-1426197297/
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dpi is the number of pixels per inch

In monitors, everyone uses dpi, but it should be ppi (pixels per inch).

In printers, dpi is meaningless, but should be important, but manufacturers fake the number.

Okay, I get that. But how does that explain why an image looks clear and clean on a 30 inch monitor when the original page is much smaller.

It has something to do with optical zoom, right? As in, it's kind of like looking at the image through a telescope.

But if that's the case, why can't optical zoom be reflected in printing size?

Dude, not everything is dpi.

How does that relate to what I said at all?
I don't get why people can't just say "it appears clean on a large monitor because reason X Y and Z".

If you can't tell the difference in quality between an image that's zoomed in 100% and one that's zoomed in 300%, you literally need glasses. Get yourself checked for longsightedness.

Depends on the printer, laser etchers improve by orders of magnitude when told to print at a higher resolution in a smaller area.

Your printer is scaling to a set resolution, so the difference between 300-600DPI is going to be kinda marginal, effectively it's looking twice as hard at the same information, taking a bigger picture and then scaling it to 8.5"x11" (2550x3300). It's taking the picture at 600DPI 5100x6600, then scaling back down to 2550x3300, effectively capturing smaller details. Conversely it's imaging at 600DPI and maintaining the 5100x6600 resolution.

It's when you start scaling smaller resolutions to fit bigger sizes that it becomes worrisome, as that scaling is truly detrimental since instead of reducing data you're expanding limited data. And Despite PNG's lossless formatting you can still see a lot of artifacting due to scaling.

It's a real world object, so you could scan it into however massive of a picture you wanted to, showing all the little fibres and whatever. It all just depends on the how good your sensor is.

>It's taking the picture at 600DPI 5100x6600, then scaling back down to 2550x3300, effectively capturing smaller details.
I see, so basically what's happening is that on your monitor the "zoom" is already happening. It's already "looking closer". But when you print it, that detail is just there for the sake of making the image clearer. If you printed out an image that wasn't "zoomed in" it would come out blurry because the smaller details were never captured in the original scan.

I'm not sure what you're trying to say. But an image scanned in 600dpi is more clear than one scanned in 300dpi.

Yeah, I get that.
It's just that the part that really confuses me is how an image that looks clear on a monitor looks much smaller and less clear when printed.

If it's clear on a 30 inch monitor it should be clear on 30 inch paper.

digitaltrends.com/photography/printing-large-photos-the-right-way-version-1426197297/

There's an artist that drew using dots. When you look up close, it looks like spots, but big. When you look from afar, you see the crisp image, but small.
When you take an image and scan it, you can tell your scanner to take a lot of close-packed samples (high ppi), so you get higher resolution which would show each minute detail, each curve of the smallest letter. You may also pick fewer more-spaced samples (low ppi), which would yield an image of small resolution. You'll see more general shapes, and lose the finer details. When viewed on a computer screen, you'll see smudges or just pixelated objects.
Both image files have the same physical dimensions, as you scanned the same picture/document, but the different ppi gives different resolutions. When your scanner creates the digital image file, it mentions the scanned ppi, the computer can calculate the physical dimensions back from it.

Printers dpi is like the artist. You can either use big brushes and put few dots to receive a low resolution printed image, or you can use finer brushes with very close pricks to receive high resolution more natural looking image.

resize the thing so that the autistic printer can understand it too.

>When your scanner creates the digital image file, it mentions the scanned ppi, the computer can calculate the physical dimensions back from it.
>When you look from afar, you see the crisp image, but small.
That actually explains it pretty clearly. Thank you. This is what was confusing me.

So it's actually the scanning telling the computer what the original size of the image was based on the relative number of pixels. It's not so much saying the size it would show up when reprinted or on a monitor itself.

Yeah, I get that now.
Basically it's all about miscommunication between the printer and computer.

It could also be just the printer being shit, or you missing the correct settings to tell it how to print properly. Maybe if you tell it to print on half a page it would look crisper.

You're both talking about dot pitch, not ppi. Dot pitch is a monitor feature for how many pixels there are in an inch.
PPI is used for scanning images. DPI is dots per inch and is used for printing images. These two are essentially hardware settings that tell the resolution.

>Can someone explain to me example how DPI is relative to monitor size and size it would be when printed.

DPI is not related to the monitor whatsoever. Software upon rendering usually scales the image so it wouldn't clip and could be viewed in full. It doesn't try to account for physical dimensions. Some software (usually vector programs) perform additional scaling to present the image as it would be appear when printed at 100% zoom. It uses a special setting that the user has to manually input that represents the physical dot pitch. Pic related is the setting in Inkscape. You're supposed to match the drawn ruler with a real one using the percentage setting. Another software, Adobe Reader, has a simple pixels/inch input.

Jesus Christ, your communication skills are absolutely abysmal. What the fuck are you talking about? I hope for the sake of other people that you never ever get a job where you have to convey any even remotely complex idea via language.

There's a printer. It takes an A4 (or Letter) page and scans it with DPI set to 300. The resulting image contains information about the size of the page, i.e. the program that displays it on your computer knows that this document is 210 mm × 297 mm in size, regardless of amount of pixels (i.e. resolution, i.e. dpi).
Now, your standard non-apple-retina non-HiDPI computer screen has a ppi of roughly 100-120, let's asume 100 for convenience, i.e. your document is thrice the resolution of your screen. That means if you tell your document reader program to display that page at 100% (i.e. the displayed document is as big as the original one, you can hold a blank piece of A4 paper over the screen, and it fits perfectly), the program can fit every third pixel in the image to a pixel on your screen, and discard two, which makes it look crisp. If you now zoom in 300%, the program can do a perfect mapping of image pixels to screen pixels, and it still looks crisp. But as soon as you zoom in higher, the software needs to start interpolating, because it's missing information. If you're zoomed in 600%, every second pixel will need to be interpolated.

Also, every zoom level that doesn't allow an even mapping of document pixels to screen pixels will look blurry, for example 183.6544846546%. Because the program has to interpolate some pixels.

additionally, some programs (those more on the image viewer side) might consider 100% zoom to mean that there is a perfect mapping of screen pixels to image pixels. But all this also depends on the nature of the file in question.

Fuck off.
Sup Forums is not Google.

That's the dumbest shit I heard all month, no wonder with people this dumb here the board sucks dildos.

>If you now zoom in 300%, the program can do a perfect mapping of image pixels to screen pixels, and it still looks crisp.
And why can't this be projected onto physical paper?

Also, I feel what I said was explained very clearly given the information I have to work worth.

Your whole explanation is basically the computer can magically vector a perfect 300% zoom.

Because people who say stuff like that, don't know enough about it to make meaningful contribution.

At this point I fear you may be a bit slow.
>And why can't this be projected onto physical paper?
What are you talking about? It's a 1:1 representation of the information scanned.
>Your whole explanation is basically the computer can magically vector a perfect 300% zoom.
No. He's saying that in his example, an image at 3X the physical size of the paper would be mapping the number of points scanned cleanly to the screen. No need to discard information, no need to guess what's between information.

The irony is that you're the slow one here.

>What are you talking about?
Why a scanned 7 inch wide page looks clean and crisp on a 30 inch wide monitor can't be printed out clear and crisp on a 30 inch wide sheet of paper.

Because it only looks 'crisp and clear' because of the screen's pixel count. In this example, I'm going to have to assume you scanned it in at the native resolution of the screen.
Remember, you're not creating any new information. You're talking about different ways of presenting the existing information. People smarter than me have explained it clear than I could've in this thread already, I advise giving it another look-over if you're still not getting this.
I think the real question you're asking here is 'why does it look crisp on the screen', not 'why can't I print it crisp but bigger'.

yes, it's theoretically possible to get the same resolution image between a 30" display and a 30" print of the same image file
there are differences in the physical construction of the image between a display and printout, though, so they won't be /exactly/ alike

one thing to consider is to try disabling smoothing of the image when printing, the printer/driver/software may be upsampling the image to make it appear smoother, but this can also make the image seem blurrier
if you can't disable this behaviour, you can also work around it it by upsampling the image ahead of time, with a point filter

What's the difference between looking crisp and clear and actually being crisp and clear?

>I think the real question you're asking here is 'why does it look crisp on the screen', not 'why can't I print it crisp but bigger'.
I guess.

Because by all logic and normal reasoning, if it's clear on a 30 inch monitor, it should be clear on 30 inch paper.

What if I just had a sheet of glass "monitor" that was 30in x 40in. It'd basically be the same as a piece of paper.

>there are differences in the physical construction of the image between a display and printout, though, so they won't be /exactly/ alike
Yeah, that makes sense.

This is just such as weird and vague topic that I for some reason just can't understand it easily. I don't know why.

I've read a lot of pages about it, but people say that things print out smaller, but no one ever really explains the theory or reason behind it.

>I've read a lot of pages about it, but people say that things print out smaller, but no one ever really explains the theory or reason behind it.
typically this is because the printer can print at a higher resolution (as in dpi) than the monitor used to preview it

for example, a common monitor may be say, 120dpi, if you view an image without scaling on it, that's the image "at 120dpi", that is, if it's a 500px wide image, it will be ~4.2in wide on the monitor
but if you print that same image at 300dpi, it will be only ~1.7in wide on the paper

if that's still not clear, dpi means dots per inch, that is, how many dots, or pixels, are [to be placed] within an inch of physical space
at 300dpi, 300px is 1in

Pretty much what I'm getting from this is you saying that the image on the monitor is not as clear as I think it is. I just can't tell otherwise because I'm not looking extremely close at the physical page.

...

that and the pixels are sharp with no bleed on a display

Kind of, yes. Rule of thumb is that you need roughly three times the DPI on paper to replicate the same clarity as on a screen.

Okay, that pretty much makes perfect sense and clears up all the confusion I had.

Thanks for baring with me and explaining it.

I think the issue was that you started out by asking the wrong question, which is why a lot of people were confused when trying to reply.

Maybe. I honestly don't know much about the subject, so I was not totally clear on how to ask.

It's alright, that you're willing to learn already puts you ahead of most people.
Screens and displays are a difficult thing to grasp at the best of times, and an intuitive understanding of the underlying maths is crucial.

Dude, as explained previously, it's a matter of scale. Your monitor has a different scale than your printer.

Take for example a map of the US, let's call it A; and then look at a map of the whole world, let's call it B. If you look at the scale it might say something like 1" -- 100 miles in A and 1" -- 1000 miles in B. Now the same inch represent different sizes in each map.

It happens the same on the printer. Like the user said before, your screen has a smaller scale than your printer, so when you want to print it and you keep the size, ON YOUR SCREEN it looks perfect (because you are previewing it on your screen) but you are not converting to the equivalent size of the page or the printers scale, but in fact increasing the size, thus creating artifacts on the page.

Read a few posts above yours.

not sure what you're trying to say here, but scaling it back down defeats the purpose of the demonstration
they look the same scaled back because they do have the same level of detail/number of pixels
the difference is that the right /seems/ blurrier (in my upscale, of course), as adjacent pixels are blurred together

Don't forget your printer also plays a role in this. Printers usually print in CMYK not RGB, also your monitors calibration and your printer profile will make the colors look incorrect unless you spend a fuck ton on a good printer and a calibrator for both.
Not to mention each printer has their own print resolution, some higher than others. Even the type of paper you use can have a difference.