My input files are 300 dpi - and I’ve noticed that the output files, whether they’re jpg or png, are 72 dpi. Is this set somewhere? I’d like to be able to keep them at 300 dpi if possible.
Interesting, what software are you using?
The DPI number in the metadata from Images are absolute uninteresting as long as the number ob pixels is the same.
True for the picture, wrong for the workflow. Especially when you have to deal with printing. E.g., this is one of the biggest issues I have with inkscape. There, the fix dpi value set to 90/96 presents me with a lot of calculator exercises when dealing with photos.
I am using Raw Therapee and GIMP. I start with an image that my camera produces that is 300 dpi. When I take the RAW file into RT, then save the output as either a jpg or png file, and then look at the result in GIMP, it’s now 72 dpi. Fine for web display, useless for serious printing.This may be “uninteresting”, but it means I won’t be using this software for anything I want to print.
And, I just checked to see what UFRaw does to a 300 dpi image: the saved result is 72 dpi. I guess either I don’t know how to set the output dpi, or “you get what you pay for” is applicable in the case of editing RAW files. 
In the case of a digital image, the only important parameter that determines the resolution is the width and height in pixels. The DPI parameter simply tells the software which size IN INCHES (or cm or mm) should be assigned to the image.
In fact, your camera does not take a 300 DPI image, because the size of the output medium is not known.
When RT saves an image at 72 DPI it does not reduce the resolution, but only changes the assigned METRIC dimensions. This can be changed later on without changing the actual pixels.
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In fact, a full frame (24 × 36 mm² ≈ 1 × 1.5 in²) camera with 24 Megapixels (4000 × 6000) takes approximately a 4000 dpi (ppi) image. SCNR 
But back on the track: While you are totally right with your explanation, asking for the possibility to set the output dpi within an image processing software is still valid, since it may change how subsequent programs deal with the picture. It’s just for convenience, nothing else, but IMO a valid concern. IIRC, in darktable you can set it in a configuration file. Found it: see meta: allow resolution to be specified via darktablerc · darktable-org/darktable@8c8615b · GitHub. Don’t know about RT, Gimp has the “print size” dialog in the “image” menu.
Someone should tell Nikon to stop lying - it says the image is 300 dots per inch (dpi). Interestingly enough, when I tried saving a 300 dpi RAW file with RT as an uncompressed TIFF file, guess what: the result is a 300 dpi image! These are figures shown both in the GIMP and in RT.
I’ve always thought that dpi was a ratio, of how many “dots per inch” were in the image, not the actual size given to the image. Sort of like mph doesn’t say how far you’ve driven, but the rate at which you’re driving. If the image is 5x7 or 8x10, the dpi doesn’t change. If you drive for an hour or two hours, your mph doesn’t change.
You can change the DPI value in Gimp:
Open GIMP. Load your image by selecting “File” from the top menu then “Open.” Browse to your image and select “Ok.”
Select “Image” from the top menu, then “Image Scale.” This will open the Scale Image dialogue. The size of your image will be listed at the top of the window in inches or pixels. Below this will be your “X Resolution” and “Y Resolution” both of which should be the same number. This is measured in “pixels/in.” which is another way of saying dpi. Enter a new value into the “X Resolution” textbox, This will automatically change the “Y Resolution” as well.
But still, this does only change a number in the metadata. This has nothing to do with the quality of the printed image.
Someone should tell Nikon to stop lying - it says
the image is 300 dots per inch (dpi).
I think lying is the wrong word. Nokia writes 300 dpi into the file because that’s a good value for a print workflow.
4000 dpi would be a technical correct value, but it is totally useless.
72 or 90 dpi would be OK for a web workflow.
I’ve always thought that dpi was a ratio, of how many “dots per inch”
were in the image, not the actual size given to the image. Sort of like
mph doesn’t say how far you’ve driven, but the rate at which you’re
driving. If the image is 5x7 or 8x10,
5x7 or 8x10 what? Pleas a a unit.
the dpi doesn’t change. If you
drive for an hour or two hours, your mph doesn’t change.
I’ll add a examples:
- The image is:
- 900 pixel x 900 pixel
- 300 dpi (ppi (pixle per inch) is more correct)
→ The Image is printed with 3 inch x 3 inch
- The image is:
- 900 pixel x 900 pixel
- 100 dpi (ppi (pixle per inch) is more correct)
→ The Image is printed with 9 inch x 9 inch
- The image is:
- 900 pixel x 900 pixel
- I need a 90 inch x inch picture
→ The image will have 10 dpi
The dpi information is only useful if you are doing things like creating a newspaper and need to place a picture in your DTP program. Then this picture gets a default size.
So, it’s just a number in the metadata - and an image that is said to be 72 dpi, will print out just as nicely as one at 300 dpi? Sure, if it’s printed at a smaller size - but 8x10 (and that’s inches) or larger, the more dpi, the better the image - the resolution is better. And yes, I know how to change the resolution/dpi in the GIMP, but was hoping there was a way of stopping RawTherapee from changing it to 72 dpi.
And for the other response: the dpi describes the resolution, whether it be 10 inches or 100 inches. Yes, there will be more pixels involved, just as if you’re driving 50 mph, there will be more miles driven, if you drive for 10 hours instead of 2 hours. If I want a good print, and I only have 900x900 pixels, yes, the dpi is going to be bad for a large image - that’s why the dpi ratio is important! It doesn’t say how many pixels there are, but the ratio, of how many per inch. AFAIK, RT isn’t setting the total number of pixels when it says 72 dpi, but the ratio. Again,I could be wrong. Regardless a low dpi is not as good as a high dpi, the larger the printed image becomes.
You are still mixing up two concepts. If I have a given print size, say 8 in by 10 in, the higher the dpi the better the printing result (roughly). If my camera has 24 MP, I will have a maximal resolution of 4000 times 6000 pixels. If I print this on 8 in by 10 in, I will get about 500 to 600 dpi (I have to crop because the aspect ratio of paper and file is different): 4000 dots (pixels) divided by 8 in equals 500 dpi.
There are three measures involved: the absolute number of pixels, the pixels per inch and the media size. Two of them given will result in the third one. That’s true for taking a picture with a camera or scanner and for outputting it, only the available two measures out of three change.
- For scanning, the media size and the scanner resolution are given
- With the camera the media size and the absolute number of pixels is given (but the media size is not important)
- For printing, the media size and the minimum required resolution is given
- Your monitor has media size and absolute number of pixels given
Within the computer, only the absolute number of pixels count, since resolution/media size depend on the output. This number of pixels may or may not be large enough to fulfil a certain output requirement. Your monitor has a low resolution of e.g. 96 dpi, therefore a small image is enough to fill the frame. Your 56 in TV may have the same number of pixels as your 22 in monitor, therefore the same small image is still large enough to fill the frame.
It is the other way around, at least in this context: it tells how large the print will be for the native resolution (in pixels) of the processed RAW file.
The DPI is meaningless if you don’t specify either the number of pixels or the output metric size.
A 300 DPI image is not necessarely better than a 72 DPI, it might well be exactly the same image at different output sizes.
In vector graphics editors like inkscape the situation is completely different, because the vectorized.image does not have a fixed size in pixels, but in metrics units. In this case an higher DPI indeed results in an output image of better quality.
I suspect that this is the source of confusion.
[quote=“lvarney, post:5, topic:1046”]
I start with an image that my camera produces that is 300 dpi. When I take the RAW file into RT, then save the output as either a jpg or png file, and then look at the result in GIMP, it’s now 72 dpi. Fine for web display, useless for serious printing.[/quote]
How did you arrive at that conclusion?
And how did you arrive at this conclusion? If it’s free it must be shit? Is that the attitude you want to assume asking for help?
Dots per inch - Wikipedia
Pixel density - Wikipedia
Please see @Carmelo_DrRaw’s reply Output file dpi changeable? - #7 by Carmelo_DrRaw
The DPI value stored in image metadata is of completely no importance or relevance and incorrect or not possible to be correct in 99% of cases.
When it comes to printing, you decide on what physical size medium you want to print on, then you set the PPI (often unfortunately incorrectly called DPI) in the printing program (typically 150 to 300 for photo quality prints), and that decides at what resolution the image gets sent to the printer. You want to aim for the photo’s resolution in pixels to be equal or larger to the resolution required to produce a print of your chosen size at your chosen PPI.
In the printer’s settings, you sometimes can set the DPI value, which decides how many droplets of ink are sprayed onto a square inch. Typical DPI values for home inkjet printers nowadays are 2400x1200 to 6000x2400. The “DPI” metadata value you refer to has nothing to do with this.
And how did I arrive at that conclusion? By looking at the properties of the images as they are saved on my computer. My camera allows me to save both a fine-quality jpg file, as well as a NEF file (I have not idea why Nikon refers to them as such, rather than RAW). I’m assuming, again, that when I look at the properties of the jpg and see that it indicates it’s 300 dpi (and no, I don’t really care if you want to refer to it as points per inch, rather than dots per inch), I’m assuming that the NEF/RAW file would not be of less resolution than the jpg file.
I disagree that the value stored in metadata is not important nor is relevant. It’s telling you the ratio between the actual size of the image, and the number of pixels/ dots it contains.Right? If you don’t consider that important, that’s your business. To refer back to another ratio I mentioned, miles per hour, you might consider that unimportant, too. But if you want to know just how soon you’ll arrive at your destination, it’s very important! And, same with dpi/ppi. If you want a good idea of how your printed output is going to look, that number is going to come in really handy. If it’s a low dpi, then you better not assume that a really large output image is going to look good. Ditto for the mph: if it’s a low number, don’t expect to get to your final destination very quickly!
Finally, that “attitude” question: I am not concluding that it’s a “piece of shit” based on its price - if that were so, I would automatically dismiss Linux as “a piece of shit”, right? Hardly. But I do assume, rightly or wrongly, that a more expensive item should come with more functions, bells and whistles, etc., than a lower-priced item. If not, then why pay more?
I am truly sorry if some of you have taken offense at my questions or comments. It just seemed odd to me that one piece of free software (GIMP) allows you to change the dpi (thus resulting in a different print recommended print size, of course), but that this software does not. I was further assuming that it would, but that I did not know how to do it. In a previous question, I had asked about why it seemed that this software was permanently changing the RAW file, and I wondered if there was a way to stop it from doing that. Luckily, I was told that it only saved the changes not permanently, and you could right-click on the thumbnail image and tell it to revert back to the original.
I was thinking of asking about a prior comment made, about “the native resolution (in pixels) of the processed RAW file” - that sounds as if the poster is saying that it’s 72 dpi, and not 300, which doesn’t seem right, given the large size of the file before it’s “processed”. But, I won’t ask about that. I’ve ruffled enough feathers asking questions about this software, and I know when to quit.
Because they are files containing raw sensor data stored in the “Nikon Electronic Format”, an acronym. Why would you capitalize “raw”?
Not points per inch. Pixels per inch. One sprays out of a cartridge nozzle, the other is a dot character in typography.
Wrong. But as you “really don’t care”, and I still don’t like your attitude, I’ll stop reading here.
And this is actually the case, despite the different DPI. This can be easily checked by opening the rawtherapee output in any image viewer and checking the image dimensions in pixels.
The DPI value does not tell you anything about the final print size and quality as long as you do not know the image size in pixels, like the speed in MPH does not tell you anything about the duration of your trip as long as you do not specify how many miles you want to drive.
It would be really a pity that you give up on such an excellent piece of software like rawtherapee only for this minor drawback with no practical consequences.
No, only the image dimensions in pixels really tell you how good the print might be at a given paper size.
This question is the key motivation of this whole site and forum: we want to demonstrate that free software can be equivalent, if not better than, expensive commercial tools. At least for all of the everyday needs of amateur and professional photographers.
and you don’t like my attitude? Sheesh! And you smirk with that "“sprays out of a cartridge nozzle” crack? And dpi, regardless if you want to call it that or ppi, does tell you how many of those items there are per inch in the image. What I “really don’t care” about, is if you want to use ppi instead of dpi.
And I don’t like your attitude, either, so there 
So, it’s just a number in the metadata - and an
image that is said to be 72 dpi, will print out just as nicely as one at
300 dpi?
An image that hast 300 dpi in the metadata will not only print out just as nicely as one at 72 dpi, it will print out exactly the same. This information is not used.
Sure, if it’s printed at a smaller size - but 8x10 (and
that’s inches) or larger, the more dpi, the better the image - the
resolution is better.
You are confusing things here.
“The more dpi, the better the image”
→ That is right. But the dpi inside the metadata has noting to do with the printed resolution (dpi) The possible dpi of the printed resolution is only defined by the size of the image in pixel and the possible resolution of the printer.
And for the other response: the dpi describes the resolution, whether
it be 10 inches or 100 inches.
No. It is dots per inch for a reason. If you change the output size you change the dpi.
Yes, there will be more pixels involved,
No, there are exactly the same number of pixels involved.
just as if you’re driving 50 mph, there will be more miles driven, if
you drive for 10 hours instead of 2 hours.
Your mph analogy does not work, because there are all units real world values. Pixels don’t have a size in the real world until you display them on screen or print them.
If I want a good print, and I
only have 900x900 pixels, yes, the dpi is going to be bad for a large
image - that’s why the dpi ratio is important!
There is nothing like dpi ratio. dpi is already the ratio of pixel per inch.
It doesn’t say how many
pixels there are, but the ratio, of how many per inch.
No, that is dpi.
AFAIK, RT isn’t
setting the total number of pixels when it says 72 dpi, but the ratio.
Again, no. RT just changes a number that is used by some programs to calculate the size of the image in inch. This information is not used if you print this image with the printer.
Again,I could be wrong.
I’m sorry to say that. But yes you are wrong.