Question about resolution in digital photography

[Dymonz]

Hi

I am brand new to DSLR photography. I've recently bought a Nikon D3200 twin lens kit and haven't owned an SLR since the days of film, probably 10 or so years ago.

I am trying to work out why my resolution may change with some photos. Most of the ones I've taken are at 300dpi which is exactly what I want, but I noticed that a few I have taken are at only 96dpi and I don't know why.

What conditions or settings change this in digital photography? I have looked at two photos taken with aperture priority. One was outside in bright conditions, the other inside under artificial light without a flash. I thought maybe low light was a contributing factor, but another photo taken in the shadowy branches of a tree without flash is also at 300dpi. Any advice will be gratefully received. Although I have used an SLR in the past, this is all new territory to me. Thanks.

[graynomad]

I've noticed similar but always put it down to settings on different bodies (I have 4) but in 8 years of DSLR use I've never looked into it, which I think shows how important it is.

Truth is I don't think it matters at the capture stage, as long as you have the full X000 x Y000 pixels your camera is capable of.

[Dymonz]

Truth is I don't think it matters at the capture stage, as long as you have the full X000 x Y000 pixels your camera is capable of.

Thanks for your answer. One thing we are considering is that the magazine my husband writes for asks for 300dpi for any photos he submits with his articles, so understanding exactly what changes the resolution is something we are trying to do. They currently send a photographer for any feature articles he writes, but there will be times when his own photography will be fine, especially when covering events. I went back to check the pixels and yes they are the maximum.

[graynomad]

Hopefully someone can explain the idiosyncrasies of this to both of us.

Meanwhile you can change the res of the photo without affecting anything else in Photoshop or similar. So when the time comes to submit make the image 300dpi then to keep them happy. Once again I doubt it really matters to them either as long as there are enough pixels for the intended use. But it is common to specify 300dpi @ the final size it will be used as that's the de-facto standard print res.

EDIT: I just looked at every menu option on one of my IDs, can't see any mention of file resolution.

[xpatUSA]

These questions appear regularly enough that there should be a tutorial on the subject somewhere.

This might help:

https://www.cambridgeincolour.com/tu...mera-pixel.htm

And then, it is helpful to use a descriptive word together with "resolution" which, by itself, is meaningless.

e.g. sensor resolution, lens resolution, screen resolution, printer resolution, spectral resolution, New Year's resolution, ya get the idea . . .

New Year's: "I resolve to word my posts as vaguely as possible so nobody can guess the question" . .

No disrepecks, folks, just my warped sense of humor showing :-)

[graynomad]

Thanks Ted, that helps a little to resolve the matter

Yes I shouldn't really use the word "resolution" either, as you say it's meaningless by itself. As I said above none of this really matters as long as you have enough pixels to do the job.

So my resolution is never to use the word resolution again unless maybe I'm talking about resolving power of a lens or something.

[xpatUSA]

Thanks for your answer. One thing we are considering is that the magazine my husband writes for asks for 300dpi for any photos he submits with his articles, so understanding exactly what changes the resolution is something we are trying to do. They currently send a photographer for any feature articles he writes, but there will be times when his own photography will be fine, especially when covering events. I went back to check the pixels and yes they are the maximum.

Hello Andrea, do pardon my earlier post, relevant though it be, was a bit sarcy.

Is the magazine of the paper printed variety? What is the size of one page, A4? A3? Does your husband have to know in advance how big each printed image will be? Do y'all use a posh photo-editor, like Adobe LightRoom? These questions are related to "print resolution" i.e. how big an image looks when printed on paper. The problem with understanding printer resolution is that the relationship is inverse - the bigger the resolution, the smaller the image.

What you need to find out is how your camera sets the printer resolution (NOT the pixel dimensions) of the image file it puts out. I've only got a D50, so can't really help you but someone here will.

For a small-size magazine you shouldn't really need maximum pixel-sized images (sorry, Rob). Some may disagree. My rationale is:

Say the biggest pic in a printed article is 5"x7" then, perhaps, one might make that 6"x9" for the magazine's folks to crop or re-size a bit. That's 6x300 high and 9x300 wide = 1800x2700px at 300 ppi. I've read that most mags accept JPEG sRGB files and perhaps we would send them at high to max quality. Like, from Adobe, a quality of 9-12 should be good enough - not that I've ever done it.

Good luck!

[graynomad]

You're right about not always needing a full size pic and I used to scale them accordingly as per your example.

These days however I always send a full size JPEG and let them scale/crop as required. I don't think I even look at the reso...oops, number of pixels any more

Rob

[Dymonz]

Hello Andrea, do pardon my earlier post, relevant though it be, was a bit sarcy.

Is the magazine of the paper printed variety? What is the size of one page, A4? A3? Does your husband have to know in advance how big each printed image will be? Do y'all use a posh photo-editor, like Adobe LightRoom? These questions are related to "print resolution" i.e. how big an image looks when printed on paper. The problem with understanding printer resolution is that the relationship is inverse - the bigger the resolution, the smaller the image.

What you need to find out is how your camera sets the printer resolution (NOT the pixel dimensions) of the image file it puts out. I've only got a D50, so can't really help you but someone here will.

For a small-size magazine you shouldn't really need maximum pixel-sized images (sorry, Rob). Some may disagree. My rationale is:

Say the biggest pic in a printed article is 5"x7" then, perhaps, one might make that 6"x9" for the magazine's folks to crop or re-size a bit. That's 6x300 high and 9x300 wide = 1800x2700px at 300 ppi. I've read that most mags accept JPEG sRGB files and perhaps we would send them at high to max quality. Like, from Adobe, a quality of 9-12 should be good enough - not that I've ever done it.

Good luck!

Haha! I laughed when I saw your earlier post, thinking "Yep, well that really highlights how new I am to all this, because I have no idea what you just said!" The magazine is printed, yes. It's A4 size and some images are full page. No, he doesn't know in advance what size they will be printed. I believe the editor makes that decision (or someone in design I guess), once they see what they have. He has Photoshop CS3 on his computer which he uses for the websites he writes. I will Google how the camera sets the printer resolution and go from there unless someone just 'knows' lol. For me, I just like to take photos to print... but the camera is there for two of us to use it for two different purposes

[xpatUSA]

I am trying to work out why my resolution may change with some photos. Most of the ones I've taken are at 300dpi which is exactly what I want, but I noticed that a few I have taken are at only 96dpi and I don't know why.

I just took some test shots with the D50 - all jpeg, large, medium, small size - fine, normal, basic quality. Then I looked at the image properties (a.k.a. EXIF properties). All had the XResolution and YResolution out of the camera at 300 ppi. Nothing in the manual says if that can be changed or not.

I opened one image in Photoshop Elements and "saved for the Web". It changed the XResolution and YResolution to 96 ppi.

Therefore, either your Nikon has an option to produce a web-ready JPEG image, or someone did the same as I just did in your CS3 Editor.

From your info above about image size, perhaps he should simply assume the worst and go for A4-sized pics (as Rob advises above) and so shoot at least 3000 x 2000 px images.

[Dymonz]

Thanks, I'll have a look at that. I've done no editing at this stage, so I will look at the settings on the camera and see if I've fiddled with something instead

[revi]

As implied by earlier answers, you don't have to care about the resolution in the metadata or for on-screen display.

For the metadata: there is no actual, physical size associated with an image file, so no resolution can be specified.
For screen display: you don't care about the screen size in inches, only about the size in pixels, so resolution in PPI
isn't relevant.
So, in practice: you can forget about PPI measures when taking or editing photos (as you cannot do much about
it anyway, other than adapting the sensor/camera you use to the final use of the image)

Now, there are a few cases where PPI values do have some importance.

There are technical reasons why printers (as in 'guys that make magazines and such', not the boxes on your desk)
want 300 PPI resolution, so if you prepare an image for them, you might have to know the final printed size in order
to give them the correct image size in pixels.
Chances are that the magazine editors will take care of that, so they'll want the largest size you can give them,
and not an up- or down-sampled version. That means that even there, you don't have to care about the resolution.

Only if you have prints done, you'll want to keep an eye on the resolution, in order to have a reasonable number of
pixels: 500 pixels/inch is never going to be a problem, 50 PPI for an A4 to be seen at 30 cm is 'a bit' on the low side
(but perfectly acceptable for a print of 1 m² to be watched from a few meters distance). Note that here also, there's
a lot of wiggle room.

As to why 'they' want 300 PPI for prints: that resolution is supposedly very close to what the average person can
see at 30 cm/12'' distance. Note that the viewing distance is important! Double the viewing distance, and you 'need' half
the resolution

This measure is based on high-contrast patterns though, for low-contrast images the eye is less discriminating. That's
why you still can get away with less pixels (say 200 PPI for reading distance) for a 'normal' photo without visible loss
of quality. And if you use a mat or textured paper, or canvas for printing, you can go even lower, as the material
hides the finest details anyway.

[Dymonz]

As implied by earlier answers, you don't have to care about the resolution in the metadata or for on-screen display.

There are technical reasons why printers (as in 'guys that make magazines and such', not the boxes on your desk)
want 300 PPI resolution, so if you prepare an image for them, you might have to know the final printed size in order
to give them the correct image size in pixels.
Chances are that the magazine editors will take care of that, so they'll want the largest size you can give them,
and not an up- or down-sampled version. That means that even there, you don't have to care about the resolution.

As to why 'they' want 300 PPI for prints: that resolution is supposedly very close to what the average person can
see at 30 cm/12'' distance. Note that the viewing distance is important! Double the viewing distance, and you 'need' half
the resolution

This measure is based on high-contrast patterns though, for low-contrast images the eye is less discriminating. That's
why you still can get away with less pixels (say 200 PPI for reading distance) for a 'normal' photo without visible loss
of quality. And if you use a mat or textured paper, or canvas for printing, you can go even lower, as the material
hides the finest details anyway.

Thanks for your comments. I can actually make some sense of this! I'll pass it onto my husband and he can talk to his editor and find out exactly what's needed before he ventures down that path. Much appreciated.

[Macmahon]

Hey Andrea
There's good stuff in what you've been given already. This (particularly the 2nd page) may help explain why they're asking for 300 dpi. However if you send the image at the greatest size, and highest quality possible, the printer should have the technology to resample to the dot pitch they need.
Cheers
Tim

[Dymonz]

Hey Andrea
There's good stuff in what you've been given already. This (particularly the 2nd page) may help explain why they're asking for 300 dpi. However if you send the image at the greatest size, and highest quality possible, the printer should have the technology to resample to the dot pitch they need.
Cheers
Tim

Thank you Tim, that's a really good read. It's going to take me a while to make my way around this site and all the information available, so I really appreciate the help you guys have offered. I'm off to have a play with the resampling options in PS too, so I can get a feel for what I can or can't do there.

[Dymonz]

Hi

Just thought I'd pop back and let you know what I played with. I've spent time with resampling in PS CS3 and think I've got the hang of it. However, I have still had the question on my mind about WHY the camera automatically changed from 300 to 96 dpi (as shown in the EXIF data) when photographing in this artificial light... and only that.

The salesperson told me that if I turned the flash off but still hand-held the camera for the shot, chances are that the camera pushed itself out to a higher ISO sensitivity. Sure enough, it was at 800 ISO. With this in mind, I manually set that to 100 ISO, mounted the camera on a borrowed tripod and dropped the shutter speed to 1 second. This gave me 300 dpi! I know from this that I am going to learn a lot about low light photography and my next immediate purchase is going to be a tripod... one of those things I'd planned to get 'next time'.

Thanks all for your ideas and links for extra reading. I'm soaking up photography magazines and helpful hints wherever I can. Your help is invaluable.

[Macmahon]

Hi

Just thought I'd pop back and let you know what I played with. I've spent time with resampling in PS CS3 and think I've got the hang of it. However, I have still had the question on my mind about WHY the camera automatically changed from 300 to 96 dpi (as shown in the EXIF data) when photographing in this artificial light... and only that.

Andrea, I'm not entirely sure why the EXIF data shows some change from one shot to the next but I'm sure that dpi is essentially meaningless for the image straight off the sensor. The sensor size is fixed. The number of pixels is fixed. And every pixel records some information. Even if the physical size of the sensor were relevant, it doesn't change either, so different dpi doesn't make sense.

If and when you have cropped the image to change the number of pixels, and if and when you've chosen to send the pixels to a medium of constrained size, then a measure like dpi becomes meaningful. The EXIF data (whatever it means) may be misleading you to worry about a non issue.

The salesperson told me that if I turned the flash off but still hand-held the camera for the shot, chances are that the camera pushed itself out to a higher ISO sensitivity. Sure enough, it was at 800 ISO.

If you have the camera on fully automatic this is quite right. In fully automatic mode the camera may adjust to a higher ISO in order to keep the shutter speed fast enough for a hand-held shot. But if the salesperson suggested this may affect 'dpi' then he/she hasn't been very helpful in this respect. The 'dpi' measure in the EXIF data of an image straight off the sensor doesn't mean anything.

However, if you inspect the EXIF data for any of your images (before you've cropped or anything like that) you will find that the image height and image width (in pixels) are always the same. That's sensible: the sensor size does not change when you open the shutter for a longer or shorter time or when you alter the aperture of the lens, nor when you change the sensitivity of the pixels (by altering the ISO) to compensate for changing light conditions. The image size is completely independent of any of those things.

... I am going to learn a lot about low light photography and my next immediate purchase is going to be a tripod... one of those things I'd planned to get 'next time'.

Nevertheless, this is a good move. A tripod will allow you to shoot with slower shutter speeds without movement blur, and lower ISOs will avoid electronic 'sensor 'noise', both of which will improve your image quality. But neither will affect 'dpi' of the image.

Cheers

Tim

[revi]

Hi

Just thought I'd pop back and let you know what I played with. I've spent time with resampling in PS CS3 and think I've got the hang of it. However, I have still had the question on my mind about WHY the camera automatically changed from 300 to 96 dpi (as shown in the EXIF data) when photographing in this artificial light... and only that.

The salesperson told me that if I turned the flash off but still hand-held the camera for the shot, chances are that the camera pushed itself out to a higher ISO sensitivity. Sure enough, it was at 800 ISO. With this in mind, I manually set that to 100 ISO, mounted the camera on a borrowed tripod and dropped the shutter speed to 1 second. This gave me 300 dpi! I know from this that I am going to learn a lot about low light photography and my next immediate purchase is going to be a tripod... one of those things I'd planned to get 'next time'.

Thanks all for your ideas and links for extra reading. I'm soaking up photography magazines and helpful hints wherever I can. Your help is invaluable.

You are doing the right thing (IMO), but for the wrong reason:
The DPI setting in the RAW/JPEG is meaningless

What you do get by using a tripod and low ISO setting is:
- a stable camera, so sharper images (unless the subject moves...)
- higher image quality, and more dynamic range due to the lower ISO.

And, if you use a tripod, you should either use a remote control to trip the shutter,
or use the time delay on the camera so it waits a few seconds after you push the button:
if you push the shutter release on the camera w/o a delay setting, you'll make the camera
vibrate, and lose (part of) the advantage of the tripod.

[Macmahon]

Hi Andrea
I just had another thought.

Is it possible that you have changed the 'image quality' setting on your camera between shots? I don't really know the Nikon D3200 but my camera offers a lot of different quality settings (of which I only use the highest quality RAW because i'm always looking to maximise print quality).
Anyway, lower quality settings not only increases compression but, in my camera anyway, also downsize the image in camera.

'dpi' in the raw image still doesn't make sense, but a lower quality image that is downsized and stored with fewer pixels would at least correlate with a smaller number for 'dpi' if it means anything at all in the EXIF data.

You may already follow the same practice that I do: leave the camera set to record at the highest possible quality. If not, I suggest it's a good practice. That way you have a chance of having sufficient pixels for high quality printing without having to upsize.

Cheers

Tim

[jcuknz]

It just goes to show that the magazine don't know what they are talking about Shoot at the highest resolution the camera is capable of ... compression is less important and some will say shoot RAW without any.

incidentally I have three cameras one apparently shoots at 80dpi, another at 180 dpi, while the third at 300dpi. Obviously one could say the last is the best camera, it was when I made those comparisons, it was a Nikon ... the Canon apparently shoots at 80dpi While my Panasonic at 180dpi ... it is all a lot of irrelevant twaddle until you get to making prints.
Obviously somebody in the printing department has told the journo one needs 300dpi for a good print and they spout it further without knowing what they are talking about