DPI vs PPI and General Discussion

The dpi stored in the meta data do refer to your printer, not to your image. Your image as a fully digital thing has no physical size and can therefore not be measured in inches via a ruler unless you have it on paper. The dpi are only from theoretical interest. If you want to print it with 300 dpi you can calculate how many pixel wide the image should be to perfectly fill an inch with pixels. Normally your printing software and the printer driver will do that work for you so don’t worry about the metadata. The metadata are missleading and do not tell anything about your image because your image has only pixels. :slight_smile:

the support mail confuses ppi (pixels per inch) which refer to your monitor with dpi (dots per inch) which refer to your printer. both ppi and dpi refer to your output device, not to the image itself. by enlarging the amount of pixels the image does not change in size unless you put it on screen or print it to paper!

Sorry, but that’s not correct. PPI and DPI both relate to printing only - PPI determines the size of the print on paper and DPI determines the quality of that print. Neither of them have anything to do with how your image is displayed on a monitor/screen which neither knows nor cares what you’ve set the PPI to in the metadata, and displays it at its own native resolution.

Put simply:

PPI is printer input
DPI is printer output.


metadata that do not refer to the image should not be saved with the image. you could save another meta data, the suggested weather when looking at the image, for example “sunshine”. and then people will complain about rain when they grabbed the photo. -.-

Please stop your crusade, which is turning into trolling, the fact of the matter is that if you choose to upscale using in/cm and dots per unit it will upscale to the calculated number of pixels. Then if you output the image without preserving the input format the new DPI settings will be written to the EXIF.

You have posted this type of irrelevant information in many places, so please stop now and help the op do what they want to do or don’t reply.

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it is not me posting irrelevant information. it’s the application. :man_shrugging:

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I know. Your description is correct. The app can only increase the number of pixels. The dpi/ppi often told in addition relies on the assumption that you will set up the printer accordingly.

Folks the difference between PPI and DPI is actually quite simple, really and they are almost the same thing but not quite as one (officially) refers to pixels and the other to (ink) dots. This link here explains it exactly in detail for anyone who is wondering or doesn’t know.
PPI vs. DPI: what’s the difference? (99designs.com)

A digital image has pixels and is first and foremost defined by the numbers of pixels in each dimension.

When printing any image (digital or not) then the image is primarily described by the size of the print, the format of the print, the print’s dimensions in inches or cm, NOT by the number of overall dots (unlike a purely digital image)!

Now (besides the maximum size of paper it can print on) every (digital) printer only has a certain maximum resolution it can print with. Every printer simply has a maximum number of DPI it can physically print.

Changing the DPI settings within the printing software (in the printing options) relates to changing the print quality settings used by the printer when printing!
So with this in mind, the maximum resolution of a printer has almost NOTHING to do with the pixels (and as such the PPI) of the digital image that it is supposed to print, other than that it naturally affects the quality of the print (the finer, the more DPI the printer can print the better).
So this printers maximum DPI and the DPI setting of the printer is a limiting factor in the print quality and on many printers it of course also very much affects printing speed as well as the consumption of ink. Therefore these printers have various DPI settings they can print with. But these printer settings are managed BY THE PRINTING SOFTWARE not by the PPI metadata stored in the image.

Now to make things a little confusing, a digital image CAN of course have PPI data written into the meta data of the image to help define size and resolution of this digital IMAGE itself.

But if an image file has PPI stored then this is typically used to define the image size (when displayed or printed or otherwise analyzed). It is merely done to relate the overall number of digital pixels to a (preferred or suggested or defined) physical dimension of the digital image.
For example an image that has 1024x768 pixels at 100 PPI would have a defined size of 10.24 inches x 7.68 inches.
This again has not really anything much to do with print quality or display resolution, at least not directly. It is merely a number stored along with or instead of a physical size of the digital image.

The main reason for using this PPI metadata is obvious:
A digital image that is intended to be used for a post card will be smaller than when used for a letter or for a large print. It may also help define the size of the shown object or may help define the dimensions of the digital map or whatever the content.
Therefore the PPI in the metadata and physical size of an image i relation to the numbers of pixels will correlate with each other.
Now this in turn CAN affect printing quality depending in the printer’s software, but (theoretically speaking) it SHOULD not.
Take the example above, a 1024x768 image could very well be printed at either 300 DPI or at 72 DPI with a size of the printed image of 10.24 inches by 7.68 inches (as defined or suggested in the image metadata with the 100PPI).

The printer’s software should define the DPI of the print and as such the print quality separately from the print size and with respect to the numbers of pixels (or the digital resolution) of the image to be printed.
The stored PPI meta data can of course be very helpful for printing an image, especially when printing quickly using standard settings without adjusting size etc. It CAN help a printing software print the image in the correct size (or not).
Some (simple and limited) software may not even allow changing the dimensions or a print and will just use the PPI information to calculate the size and print it in whatever size this results in. But that is really just a very limited and simplified way of doing print jobs and in most cases certainly not a high quality solution to the task.
“Proper” printing software will internally scale the image up (or down) to print it in the desired dimensions and will print all the necessary ink dots (at the printers highest or chosen DPI setting) to achieve a best possible or optimal print quality (according to the settings in the printer software). Some printing software does a better job at this than other printing software, some will consider PPI metadata in an image file smartly while other printing software may not.

So storing and editing the PPI metadata in an image file does NOT equate to changing the DPI quality settings in the printer software (defining how fine the dots of a print are placed on the paper by a printer when printing)!

These are two very different things!
Although one can course affect the other depending on the printing software and the printer used. (And when creating or saving PDF files and other documents tall his is again somewhat different, but that is not to be confused with the image metadata we are talking about here.)

I hope this helps resolve some of the confusion and helps understand the difference between PPI and DPI a little better even though they are not seldomly used quite interchangeably. But at least then you can still be aware of printer quality settings (or physical display resolution) and the actual resolution of the digital image file.

Last but not least about the file size of an image upscaled with Gigapixel AI:
If you’re working with compressed images such as jpg files then Gigapixel compresses the upscaled image before saving it. There seem to be no options for changing the compression quality settings in Gigapixel AI.
So as a result it appears that Gigapixel AI may compress an upscaled image more than the given original image was compressed resulting in a smaller file size than the original despite the higher resolution.
In what way or form this may or may not (negatively) affect image quality of the upscaled image, I am not sure, but most compression formats have different methods of file compression and some of them can very well produce smaller files with higher image quality than others but will typically require significantly more computing when compressing the image.
I have only noticed this paradox of upscaled image files being smaller than the original myself when using Gigapixel AI v 7.0.2.
This is a surprising phenomenon, but not necessarily a bad thing, most likely quite the opposite. But to know that it would require testing and detailed image comparisons of numerous images with very different content.
So to sum it up.
A resulting smaller file size after upscaling an image with Gigapixel AI is in most cases probably just a really good bonus thing and not something bad to worry about.

This file size phenomenon is really something for developers and professionals to think about, maybe Topaz Labs might want to consider offering quality options for exporting compressed images such as jpg and other file formats.

To finally come to and end… you can actually also even downscale images with Gigapixel AI. This can indeed very much make sense in some cases, and maybe even more so if the image compression methods used in Gigapixel might really be very efficient and provide small files at comparably good quality. But that is really something for professionals to test and decide and recommend or criticize on.

It is not irrelevant but just the plain truth.

The main issue here is that it strongly depends on your printing application if it will read the metadata and use the stored info for printing. Even professional printing service companies sometimes do not work with the included metadata. :frowning:

You need to stop this rubbish, the op wanted to know HOW to update NOT your opinion.

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Many users are confused by the dpi they set up in the application and which are stored in the meta data. Even if someone set it up and saved it right the result on paper might be wrong. I can only explain why and how things come together. A basic understanding is mandatory to archive the desired results. :man_shrugging:

Just stop, if someone wants to know how to resize using pixels per unit either help or be quiet.

Yep, including you judging by the half truths you’ve been posting recently.

Not if you don’t understand it yourself.

People seem to be managing quite happily without it.

You’ve been asked to stop it, so stop it. This is your final warning.

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@Imo @PaulM @AiDon

Let’s regroup on what the purpose of this forum is; to support one another in getting the most out of our Topaz Labs apps. While I understand that certain personality conflicts can emerge, we will not tolerate bullying.

If you do not wish to engage with a specific user, please do not reply. If you see something that is crossing the line, flag it and we will moderate as needed.

Lastly, as a team, we greatly appreciate each of your contributions to this community. The testing and support you all have provided is invaluable.

As a Moderator on this forum I have done so with repeated requests but he does not stop, if he repeats next time I will utilize other moderation tools.