dpi...?? (1 Viewer)

westley byford · Apr 2, 2010

ive noticed on some peoples pictures that there 300+ dpi.
mine are under 100.. now i dont understand anything to do with this but common sense tells me that the higher the dpi the more detail allowed in the pic. is this right?
if so how would i make mine greater, its a canon 450d??

regards wes

Roy C · Apr 2, 2010

Hi Westley, the DPI is a printing function and does not make any difference to web shots - you can set it to 72 dpi or 1000 dpi and the file size and quality will be just the same.

When it comes to printing the dpi determines the print size and quality - say you have a pic that is 2100 pixels wide and you print at 300 dpi then it will be 7 inches wide (2100/300) if you set the dpi to 200 then it will print at 10.5 (2100/200) inches wide but quality will be reduced.

Hope this helps.

P.s. 300 dpi used to be the standard for good quality prints but today's ink-jets can produce superb results at 200 dpi or even less.

westley byford · Apr 2, 2010

that cleared that up then lol

every day's a school day ha....

cheers
wes..

daveofficer · Apr 2, 2010

the easiest way to resize pics is to adjust the resolution. as royc says it's mainly useful for printing. as a rule i resize all my web images to 72dpi and keep the maximum length to 800/1000 pixels so that if anyone pinches them they'll print out crap but still look good on a monitor. all my print pics are 300dpi. the only time i scale up is for stock agencies who sometimes need bigger file sizes so i keep it at 300 dpi and increase the maximum length which results in a file size big enough to keep stock companies happy.

if you're not printing your pics then you're fine to keep them at 72 dpi. it's a bit of a fallacy to say it doesn't affect file size though as decreasing the resolution from 300 dpi to 72 dpi will result in a dramatically smaller file both pixel and mb wise. set it to 1000 dpi and it will be a much bigger file and may result in a loss in quality depending on the method of upscaling(digitally increasing the size of the image).

westley byford · Apr 2, 2010

right, just had a look at my pics, there 72dpi, there are a few of my kids that in time i will want to print off, can i upscale these or does it have to be set in the camera prior to taking pics? sorry but i havent a clue...

wes

daveofficer · Apr 2, 2010

westley byford said:
right, just had a look at my pics, there 72dpi, there are a few of my kids that in time i will want to print off, can i upscale these or does it have to be set in the camera prior to taking pics? sorry but i havent a clue...

wes

it depends how big you want to print them wes. what's their dimensions at 72dpi? if they're 72dpi but are pretty big then you'll likely get away with printing them, at least for small prints.

westley byford · Apr 2, 2010

4272x2848

i would like canvas prints, probably about 20"x14".. and normal prints about 10x8.

Roy C · Apr 3, 2010

westley byford said:
4272x2848

i would like canvas prints, probably about 20"x14".. and normal prints about 10x8.

If you are sending them away to be printed then you do not have to worry about the dpi as the printer will take care of all, giving you the best quality based on the pixel size and the print size you require. You do, however have to be aware of the quality you will get - say you have a 2000 pixel wide shot and you want it printed 20" wide then you can only print at 100 dpi so quality would not be great.

What you do have to take in to consideration is the size proportions: you say you have a file that is 4272 x 2848 this is 1.5:1. If you had a 12 x 8 print (or 6 x 4) then you would get the full frame but if you wanted a 10 x 8 then there is bound to be some cropping by the printer - a lot of on-line printer give you a crop box for you to select the exact cropping you want when your pixels dimensions do not match your desired print size.

Roy C · Apr 3, 2010

westley byford said:
right, just had a look at my pics, there 72dpi, there are a few of my kids that in time i will want to print off, can i upscale these or does it have to be set in the camera prior to taking pics? sorry but i havent a clue...

wes

This depends on the printer software you are using, some times you can stipulate the finished size you want and it will take care of the DPI for you while sometimes you will need to do it your self in a software dialog box - you are not up scaling by changing the DPI, you are just giving the printer instructions as to the size you want. For this type of printing you just work out the print size you want and set the dpi to suit.
example: if you a 4272 x 2848 pixels image and you want a 12 x 8 print then set the dpi to 356 (4272/356 = 12) and (2848/356 = 8)

Roy C · Apr 3, 2010

daveofficer said:
if you're not printing your pics then you're fine to keep them at 72 dpi. it's a bit of a fallacy to say it doesn't affect file size though as decreasing the resolution from 300 dpi to 72 dpi will result in a dramatically smaller file both pixel and mb wise. set it to 1000 dpi and it will be a much bigger file increasing

I am afraid you are 100% wrong there Dave - changing the DPI of a shot will have absolutely no effect whatsoever on the file size - if you do not believe me just try it, save a pic at say 72 dpi and note the file size, now save the same shot it at 1000 dpi and note the file size. I will guarantee they are exactly the same.

tjsimonsen · Apr 3, 2010

Roy C said:
I am afraid you are 100% wrong there Dave - changing the DPI of a shot will have absolutely no effect whatsoever on the file size - if you do not believe me just try it, save a pic at say 72 dpi and note the file size, now save the same shot it at 1000 dpi and note the file size. I will guarantee they are exactly the same.

True enough Roy.

What I think confuses some here is that many programs (certainly PS CS2) will automatically upscale/downscale the true (pixel) dimensions of the image in order to retain the perceived (printed) dimensions of the images with the new dpi resolution.

Thomas

daveofficer · Apr 3, 2010

tjsimonsen said:
True enough Roy.

What I think confuses some here is that many programs (certainly PS CS2) will automatically upscale/downscale the true (pixel) dimensions of the image in order to retain the perceived (printed) dimensions of the images with the new dpi resolution.

Thomas

yea i that's what i meant with my post. most programs when you change the dpi will adjust the image automatically so it will change the file size in most cases.

Roy C · Apr 3, 2010

tjsimonsen said:
True enough Roy.

What I think confuses some here is that many programs (certainly PS CS2) will automatically upscale/downscale the true (pixel) dimensions of the image in order to retain the perceived (printed) dimensions of the images with the new dpi resolution.

Thomas

Yep, you are right there Thomas. What you have to do in order to just change the DPI and not the pixel dimensions is to uncheck the 'resample image' box. If you do not do this then the pixels are automatically upscaled or down scaled like you say and to rectify this you have to manually type in the original pixels dimensions after changing the DPI.

Roy C · Apr 3, 2010

daveofficer said:
yea i that's what i meant with my post. most programs when you change the dpi will adjust the image automatically so it will change the file size in most cases.

Dave, see my post above. you do not have to upscale/downscale in order to change the DPI. Upscaling and changing the DPI is two very different things.

daveofficer · Apr 3, 2010

Roy C said:
Dave, see my post above. you do not have to upscale/downscale in order to change the DPI. Upscaling and changing the DPI is two very different things.

hi roy, thanks for clarifying. i guess the confusion comes from the automatic resampling by image editing software.

i am aware that it's different but while the image software does it for you they are intrinsically linked. i'll let you carry on with giving much clearer explanations than i can muster and i'll try not to confuse things further

paul goode · Apr 3, 2010

I never save anything at 72dpi or have the resolution in the crop tool set to 72 dpi just in case I inadvertently save an image thats been sized for printing at 72dpi. It shouldn't happen but I ain't perfect and mistakes can be made.
I only set a resolution when I'm saving an image for printing at either 254 or 300dpi depending on which print lab are doing the printing. Personally I ensure that an image is sized correctly at the right dpi and with the correct profile before I send it to a printer.
Files saved for web use will be at any old dpi but as pointed out above it doesn't matter.

Roy C · Apr 3, 2010

To avoid any confusion on this subject HERE is a very good explanation about it all.
Just go into the 'all about DPI ' section, it is very well written IMO and far better than I could ever explain it.

What I find unbelievable is that some print shops still ask that clients send their shots at xxx DPI (usually 300 dpi) instead of asking for what they really want, e.g. a shot of certain pixel sizes that will give a acceptable print of a given size. Asking for a certain DPI can lead to all sorts of confusion and often people will sometimes inadvertently upscale their shot which will results in poor print quality.

A while ago I was asked for a high res shot to include in a magazine at around 6 x 4 inches. I duly sent them the shot which had more than adequate number of pixels to produce the shot they wanted. They came back to me and said they wanted it at 300 DPI :-O - I explained that they could change it themselves to whatever DPI they wanted without effecting the IQ one iota. The guy still did not understand so I just changed the DPI and re-sent the identical image. Unbelievable but true.

Thankfully most of the on-line print shops are now clued-up enough to know that they can change the DPI at will and will not burden the customer with changing it.
I send all my shots away at 72 dpi, obviously ensuring that there are enough pixels to produce the print size and quality I want.

For home printing I have a piece of software that will output to the size I stipulate without me having to mess around with changing the DPI. So for sending to a print shop or printing myself I have no need to ever change form 72 DPI.

Roy C · Apr 3, 2010

Westley, you must be getting quite confused now with all our off topic stuff LOL. Just to set the record straight and answer your original question, DPI has NOTHING to do with digital image quality!

paul goode · Apr 3, 2010

Well , I've read that Roy and it all makes perfect sense.
Trouble is it wouldn't help if your lab was Proam or Peak Imaging who strictly specify the format files must be submitted in. Do we take it from the arrogant tones of your post and the article you linked you that these labs are populated by bone idle lay abouts who merely want an easy life or is there more to it.

Roy C · Apr 3, 2010

paul goode said:
Sorry Roy, I know this off topic to the OP but i don't understand your reluctance to supply a correctly sized image to a lab. I supply a file which will be for, say, a 20"x16" @ 254dpi. If it needed upsizing I'll have done it in genuine fractals and quality won't be an issue.
And that is what i want back. I don't want the lab to guess anything, not sizing, not colour correction, nothing. Its dead easy and gives me total control. I just can't see the point of sending a print file at 72dpi. As you say you've had to check the pixel dimensions which takes time, why bother?

Paul, If I have an image of say 3000 x 2000 pixels and supplied it at 72 dpi for a 12" x 8" print Then the resultant print quality will be identical to the file if I had sent the a 3000 x 2000 pixel image at 250 dpi.
In the case of of a 3000 x 2000 image at 72 dpi the lab would automatically set the dpi at 250 anyway if I wanted a 12" x 8" print so why should I bother ?

Similarly with your example. If you want a 20" x 16" print and supply a 5080 x 4064 pixel image at 72 dpi you will get exactly the same quality print that you would have if you supplied a 5080 x 4064 image at 254 dpi.

If I had a 5080 x 4064 image and wanted it printed at 10 x 8 I would still give them the exact same file that I would have if I wanted a 20 x 16 print - the only difference being that the 10 x 8 would be printed at 508 dpi and the 20 x 16 would be printed at 254 dpi. The actual dpi that I supply is irrelevant.
It is the same if I wanted several different size prints from the same image, say 20 x 16, 10 x 8 and 5 x 4, I would only sent one file and the print dpi would be auto calculated according to the pixel dimensions.

It is the same with my home printing software - I supply the image and stipulate the size I want and the programme calculates the dpi.
As I never upsize my shots then I never need to change the dpi from 72 it is a non entity as far as I am concerned.

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