how to find a photos DPI for printing to insure good print quality.

dannylightning

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how do i find out the Dpi of a jpeg image, i have a few people interested in buying prints and i want to find out which ones will be good or bad quality for printing.. i know some of my photos are not going to cut the mustard for high quality descent size prints because the photos are cropped heavily.

16 x 20 or 11 x 14 prints are probably the sizes i will try to sell the most, that is if the photo will be a good quality print in that size.. they can get smaller prints if they want but ill probably try to push the 11 x 14 prints since those are the largest that are still relatively inexpensive to get printed.

here are the specs that seem like they could possibly be of help in figuring this out on the photo i am viewing now, if any of these will tell me what i need to know please let me know how to figure it out from these specs.

file size 8.1mb

dimensions 3778 x 2519 pixels.

x resolution 240
y resolution 240

focal plane x resolution 2258.64
focal plane y resolution 2558.26

CCD Width 14.8
 

Ysarex

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You're looking for ppi (pixels per inch) not dpi (often gets confused). To find size over resolution for your image take the longest of your two pixel dimensions and divide by the resolution you'd like to use: 3778 / 300 = 12.5. That photo then will give you a 12.5 inch long photo printed at 300 ppi. To make a larger print you need to lower the ppi. So 3778 / 200 = 18.9. At 200 ppi that photo will give you a print that is 19 inches long.

You can of course do the same with the short side: 2519 / 300 = 8.4. So printed at 300 ppi your photo would make an 8.4 x 12.5 inch print.

Joe
 

The_Traveler

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Ysarex is correct, as usual, but I want to add that I ried Alien Skin Blow Up 3 to enlarge images and I was very impressed.
I'm a bit pressed for time until next weekend so I can try printing the enlarged image but will report back on that.
 
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dannylightning

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wonderful, math, not my strong point lol..

the print lab shows me DPI of the photo after i upload it and choose the size which is time consuming so figuring it out on my own should be the easiest way..

it says 300 DPI or higher is going to be the best quality.. unless i misread it and it said PPI. i have no clue what DPI is but i though that is what it said.

thanks for that info..
 
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dannylightning

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so i got a 2904 x 1963 pixel image.

2904 / 300 = 9.69
1963 / 300= 6.55

so that would give me a 9.5 x 6.5 print correct..
 

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No. It would give you a 9.7 " by 6.6" print.

Also they don't make print paper that is 9.5 x 6.5.
But you can have the print made on oversize paper, like 10 x 8, so it will have some blank border that the 9.7" x 6.55" image doesn't cover.

I your Nikon's have an APS-C size image sensor the photos made have an aspect ratio of 3:2. The aspect ratio describes the ratio of the sides of a rectangle. 3 / 2= 1.5 so the long side of a 3:2 aspect ratio rectangle is 1.5x longer than the short side.

An 8x10 has an aspect ratio of 5:4, meaning it is closer to square (1:1 - all side are the same length) . 5 / 4 = 1.25 so the long side of a 5:4 aspect ratio rectangle is 1.25x longer than the short side.

But you can also fine tune the print resolution (PPI).
2904 px / 10 inches = 290 ppi
1963 px / 290 ppi = 6.8"

The upshot is that you've cropped your image to a non-standard aspect ratio. It can still be printed as is but won't fit exactly on standard size print papers.
 
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Ysarex

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wonderful, math, not my strong point lol..

the print lab shows me DPI of the photo after i upload it and choose the size which is time consuming so figuring it out on my own should be the easiest way..

it says 300 DPI or higher is going to be the best quality.. unless i misread it and it said PPI. i have no clue what DPI is but i though that is what it said.

thanks for that info..

It's one of the most common cases of sloppy usage in the business so you really need to learn to interpret what someone means to say in context as opposed to what they say. PPI is pixels per inch and identifies the resolution of your image. It would also be the appropriate measure of a scanner's resolution. DPI is dots per inch and those dots are the dots of ink on a piece of paper. Your photo doesn't have dots and prints don't have pixels.

It creates considerable confusion unfortunately because every now and then someone sees a number that doesn't make sense to them. Just happened to me this past Wednesday in class. One of my students looked a little harder at the Epson printer driver as she was making a print and noticed that the printer was set to print at 1440 dpi. She called me over and asked, "Isn't that supposed to be 300 dpi? My photo is supposed to be 300 dpi right?" So I said, "no, if your photo is 300 ppi then that should be 2400 dpi but, don't worry it's OK." I told her I'd explain on Monday but maybe by then it'll go away and I won't have to suffer to agony of trying to explain something with math in it to college art students.

The problem occurs when people draw the logical conclusion from the sloppy usage that there's a one to one direct correspondence between image ppi and printer dpi (like my student). If you think about a printer placing a dot of ink on a piece of paper and then consider that the printer may have in total 6 or 8 ink colors then you should eventually wonder how the printer can manage a range of tone from light to dark. This is achieved by using the paper base as white and increasing ink density to achieve darker tones. Printer dots don't get bigger and smaller. So to get that tone variation it's necessary that the printer be able to lay down dots at a much higher resolution than the resolution of the image. 300 ppi in the photo requires 2400 dpi from the printer if you want a full tone photo covering a range of 256 shades of light/dark.

Joe
 
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dannylightning

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wonderful, math, not my strong point lol..

the print lab shows me DPI of the photo after i upload it and choose the size which is time consuming so figuring it out on my own should be the easiest way..

it says 300 DPI or higher is going to be the best quality.. unless i misread it and it said PPI. i have no clue what DPI is but i though that is what it said.

thanks for that info..

It's one of the most common cases of sloppy usage in the business so you really need to learn to interpret what someone means to say in context as opposed to what they say. PPI is pixels per inch and identifies the resolution of your image. It would also be the appropriate measure of a scanner's resolution. DPI is dots per inch and those dots are the dots of ink on a piece of paper. Your photo doesn't have dots and prints don't have pixels.

It creates considerable confusion unfortunately because every now and then someone sees a number that doesn't make sense to them. Just happened to me this past Wednesday in class. One of my students looked a little harder at the Epson printer driver as she was making a print and noticed that the printer was set to print at 1440 dpi. She called me over and asked, "Isn't that supposed to be 300 dpi? My photo is supposed to be 300 dpi right?" So I said, "no, if your photo is 300 ppi then that should be 2400 dpi but, don't worry it's OK." I told her I'd explain on Monday but maybe by then it'll go away and I won't have to suffer to agony of trying to explain something with math in it to college art students.

The problem occurs when people draw the logical conclusion from the sloppy usage that there's a one to one direct correspondence between image ppi and printer dpi (like my student). If you think about a printer placing a dot of ink on a piece of paper and then consider that the printer may have in total 6 or 8 ink colors then you should eventually wonder how the printer can manage a range of tone from light to dark. This is achieved by using the paper base as white and increasing ink density to achieve darker tones. Printer dots don't get bigger and smaller. So to get that tone variation it's necessary that the printer be able to lay down dots at a much higher resolution than the resolution of the image. 300 ppi in the photo requires 2400 dpi from the printer if you want a full tone photo covering a range of 256 shades of light/dark.

Joe

thanks.

you know i am on the print labs site right now just to double check.. i uploaded a photo and it is telling me what the DPI quality is for that photo in the print size i selected.,

its not telling me what the PPI is, it definitely says DPI.
 

KmH

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They and most print labs are using the term incorrectly because they figure the average consumer can't be bothered to understand the difference between DPI and PPI.

PPI is an input file value. DPI is an output file value.
 

Ysarex

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wonderful, math, not my strong point lol..

the print lab shows me DPI of the photo after i upload it and choose the size which is time consuming so figuring it out on my own should be the easiest way..

it says 300 DPI or higher is going to be the best quality.. unless i misread it and it said PPI. i have no clue what DPI is but i though that is what it said.

thanks for that info..

It's one of the most common cases of sloppy usage in the business so you really need to learn to interpret what someone means to say in context as opposed to what they say. PPI is pixels per inch and identifies the resolution of your image. It would also be the appropriate measure of a scanner's resolution. DPI is dots per inch and those dots are the dots of ink on a piece of paper. Your photo doesn't have dots and prints don't have pixels.

It creates considerable confusion unfortunately because every now and then someone sees a number that doesn't make sense to them. Just happened to me this past Wednesday in class. One of my students looked a little harder at the Epson printer driver as she was making a print and noticed that the printer was set to print at 1440 dpi. She called me over and asked, "Isn't that supposed to be 300 dpi? My photo is supposed to be 300 dpi right?" So I said, "no, if your photo is 300 ppi then that should be 2400 dpi but, don't worry it's OK." I told her I'd explain on Monday but maybe by then it'll go away and I won't have to suffer to agony of trying to explain something with math in it to college art students.

The problem occurs when people draw the logical conclusion from the sloppy usage that there's a one to one direct correspondence between image ppi and printer dpi (like my student). If you think about a printer placing a dot of ink on a piece of paper and then consider that the printer may have in total 6 or 8 ink colors then you should eventually wonder how the printer can manage a range of tone from light to dark. This is achieved by using the paper base as white and increasing ink density to achieve darker tones. Printer dots don't get bigger and smaller. So to get that tone variation it's necessary that the printer be able to lay down dots at a much higher resolution than the resolution of the image. 300 ppi in the photo requires 2400 dpi from the printer if you want a full tone photo covering a range of 256 shades of light/dark.

Joe

thanks.

you know i am on the print labs site right now just to double check.. i uploaded a photo and it is telling me what the DPI quality is for that photo in the print size i selected.,

its not telling me what the PPI is, it definitely says DPI.

I understand and I'm sure lots of other lab websites will do the same. They know the difference but it's likely, as Keith suggests, that they would chose to deliberately misuse the terms because they expect the majority of their clients misuse the terms and it's best not to confuse them.

Do a Google search for dots per inch and this is the first thing that comes up: "DPI stands for Dots Per Inch which technically means printer dots per inch. Today it is a term often misused, usually to mean PPI, which stands for Pixels Per Inch. So when someone says they want a photo that is 300 dpi they really mean that they want 300 ppi."

This is copied from the Canon spec sheet for the Pro 100 printer:
Print Resolution -- Color: Up to 4800 x 2400 dpi Black Up to 4800 x 2400 dpi. Assume the lower number is the real resolution of the printer and so use 2400 dpi to calculate how big your file will print. Surely if the printer prints at 2400 dpi you wouldn't want your photo to be only 300 dpi.

Joe
 
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dannylightning

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thanks guys. i appreciate all the good information.
 

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I don't know where you are having your photo's printed but if you're in Akron I highly recommend driving over to Campus Camera in Kent and talking to Sue in the imaging lab. She can explain anything you need to know in person and to top it off she does amazing print jobs.
Professional Imaging Lab – Campus Camera & Imaging – Kent Ohio
 
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dannylightning

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I don't know where you are having your photo's printed but if you're in Akron I highly recommend driving over to Campus Camera in Kent and talking to Sue in the imaging lab. She can explain anything you need to know in person and to top it off she does amazing print jobs.
Professional Imaging Lab – Campus Camera & Imaging – Kent Ohio

awesome, ill have to check them out. i was trying to find a local print lab but everyone i talked to did not seem to know of any good ones in the area. i might head up there and get a few prints made and see how they turn out.
 
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dannylightning

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will 200 ppi, be good for printing at a good print lab, i usually use adorama. some one was telling me they did some prints in 150 ppi on their own inkjet printer and they turned out great.

at 200 ppi according to the print labs quality bar. it shows red for bad quality, yellow for descent quality and green for good quality. a photo at 200 dpi i showing dead center on the quality bar which is right in the center of the yellow part of the bar.

at 200 ppi most of my photos will print out at 11x14 at 300 ppi most of them will print out at 8x12 i wold like to be able to offer both sizes if possible.
 

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