Megapixels , dpi and large prints - help!

C

calito

Active member
Can somebody explain to me the relationship between megapixels and dpi.

Also is it possible to shoot a photograph with 10 megapixel digital slr like the Nikon D200 and make an large print, billboard size. If yes, what would be the procedure.
What kind of file (jpeg, raw, file ?)
Thank you for your help guys.
 
There is no relation. DPI value in the file is there only to control printing.

True resolution is what the pixel count says.

DPI value which is embedded to the file is basically there to tell the printer to print the picture at a certain output resolution, which then dictates the size of the print.

Let's say you have a 3000x2100 pixel file and the DPI flag is set to 300 dpi. This combination would print a 10x7 inch print with 300 dots per inch resolution (10*300=3000 and 7*300=2100).

Large posters are printed at really low resolutions, like 50 dpi or even less. At 50 dpi this same pixel size file would be 60x42 inches.

It is true that with large posters you would have to artificially enlarge the file in Photoshop, but the consolation is that a 10 Mpix file still has more resolution* than any 35mm slide or negative, and plenty of good posters have been made from those.

*) if the lenses used are not the limiting factor.
 
Highest quality JPG is fine.

If you do a lot of manipulation with intermediate saves better keep the file as TIFF untill it is ready. Consecutive saves after changes in JPG format piles up the artefacts*. So better manipulate in TIFF, then convert to highest quality JPG for transfer to printer.


*) this was tested in out printing house, actually the quality loss was noticed on a printed page after 7 JPG HQ saves, so this in not a major concern for most of us.
 
I guess this is somewhat related to this thread that hasn't been seen in a while, so I thought I'd post here rather than start a new thread.

I'm having a family portrait taken of 11 people outdoors (8 adult, three kids 2&under). It's a gift for our parents and we are going to blow it up to larger size (maybe 20h x 24w, not sure of dimensions).

I'm wondering what minimum requirements are needed for the camera? I'm not a still photographer and won't be taking the picture, but my photog. is a little uncertain about these things.

Can someone suggest minimum megapixels of camera, dpi to shoot at (if that is a factor) and anything else that would help. I'm not sure what her camera is, but also have access to a Nikon D40 - would that be sufficient?

Thanks, and as always, if this info is available elsewhere I apologize and ask you to point me there.
 
Petrus said:
....but the consolation is that a 10 Mpix file still has more resolution* than any 35mm slide or negative
Click to expand...

Um, since 35mm slides or negatives are not digital then I'm not sure what you are trying to say by this. You can take a 35mm slide, have it scanned, and have much more detail than you can with most consumer digital SLRs. Not to mention stuff like the moiré effect and bayer interpolation......it's hard for me to bite on that statement.
 
35mm negatives can resolve much more than 10 MP with a good drum scanner. The amount it can be scanned at is also dependent on the film stock you are shooting with.

Also not all 10MP images are created equally. The amount you will be able to blow your photo up without it looking too soft will depend what lens you were shooting with, making sure your focus is spot on (including not having motion blur) your ISO/noise rating and most importantly making sure you are shooting at the preffered aperture settings of the lens (not wide open or the next couple of stops and not past f11 most likley)

All that being said, I wouldn't worry about the difference between a few megapixels. In the end the difference between a 10mp and a 20mp camera is the difference between a 9"x6" and a 12.6" x 8.4" print (@170.6 DPI).

Bottom line is that the most important thing is to make sure you have a good lens and use it properly. (just an FYI my sharpest lens is not my $1,000 L series its my $80 50mm 1.8)


In regards to file format, JPEG or TIFF is good but make sure to apply some sharpening to the photo when you are ready to export (even if its just for the web)
 
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Proper Megapixels for large portrait

Proper Megapixels for large portrait

I sort of highjacked this thread (though it was dead for over a year), but it seems to have been re-hijacked. Any thoughts on my OP or should I just start a new thread?

bigteethproductions said:
I guess this is somewhat related to this thread that hasn't been seen in a while, so I thought I'd post here rather than start a new thread.

I'm having a family portrait taken of 11 people outdoors (8 adult, three kids 2&under). It's a gift for our parents and we are going to blow it up to larger size (maybe 20h x 24w, not sure of dimensions).

I'm wondering what minimum requirements are needed for the camera? I'm not a still photographer and won't be taking the picture, but my photog. is a little uncertain about these things.

Can someone suggest minimum megapixels of camera, dpi to shoot at (if that is a factor) and anything else that would help. I'm not sure what her camera is, but also have access to a Nikon D40 - would that be sufficient?

Thanks, and as always, if this info is available elsewhere I apologize and ask you to point me there.
Click to expand...
 
You could use the D40, but I wouldn't blow it up as large as you are suggesting. I would suggest 8MP or larger for that size.
 
bigteethproductions said:
I guess this is somewhat related to this thread that hasn't been seen in a while, so I thought I'd post here rather than start a new thread.

I'm having a family portrait taken of 11 people outdoors (8 adult, three kids 2&under). It's a gift for our parents and we are going to blow it up to larger size (maybe 20h x 24w, not sure of dimensions).

I'm wondering what minimum requirements are needed for the camera? I'm not a still photographer and won't be taking the picture, but my photog. is a little uncertain about these things.

Can someone suggest minimum megapixels of camera, dpi to shoot at (if that is a factor) and anything else that would help. I'm not sure what her camera is, but also have access to a Nikon D40 - would that be sufficient?

Thanks, and as always, if this info is available elsewhere I apologize and ask you to point me there.
Click to expand...


The higher the mexapixel the better the pict is a myth, mostly created by marketing gurus and there is no science behind it. If you take 20 "10 megapixel cameras", take the same picture with each of them and look at the print for each, you will see an obvious scale going from mediocre to great. The Megapixel is less than half the story, sort of the engine horspower in a car. What is most important beside the optic on the camera, is the actual quality of each pixel, and how they relate to each other.... I won't bore you with details as you can find many white paper written on the subject on the web, but to answer your question, the D40 is plenty if you know how to use it well. I have seen very large print (small billboard size) from shots taken with a D70 (6 megapixel), and the print were incredible.
 
Cool, thanks for the help.

As it turns out I had a brief dyslexic moment and apparantly we have access to a CANON 40D, not the Nikon D40 (confusing to a non-photo person like me!).

So, as long as I have faith in the photographer then I should be able to get a nice quality family photo blown up with the Canon?
 
The D40 and 40D are two totally different animals. The 40D will be perfect for the detail you would like in a portrait. I've blown up photos from my D40 pretty large, and they are ok for non-portrait work, but I would prefer the detail the Canon gives in this instance over something like the D40.
 
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