View Full Version : DPI setting
Hello everybody
you will be able to tell by this question my serious lack of digital nouse.
I recently bought a canon 20D, which i mainly use for recording my work (sculpture)
I like to save my images at 300dpi as this, i am informed is the best size for printing postcards, images in books etc.
I also have an old nikon coolpix which does this, but cannot find how to do this on the canon.
It just appears to save all images at 72DPI
Any ideas ?
Hmmm! I thought all cams recorded at 72 dpi, even when using the best image quality settings ... I dont know about RAW though as I dont use it.
What prog do you use to edit your pics?
I use Photoshop to edit my pics, I click Image>Image Size, and there at the bottom, where it says resolution, just change the 72 to 300.
Voila!
Hth, Im sure someone with more know how will be along to help shortly!
mine are 300dpi on mine too
Hi
thanks for responding,
i use photoshop and am preety sure you can decrease the size of a file...ie 300 to 72 but not the other way around ?
hey double T,
were yours set at 300dpi when you bought the camera ?
you can increase the file size, but it can look a bit pants. What settings are you using on the cam for image capture?
*moved to correct forum
hey double T,
were yours set at 300dpi when you bought the camera ?
im not sure, first thing i done when i turned the camera on is put all settings to large, fine ,high detail then too a picture
matty
it is a canon eos 20d
Lets take a 4MP image at 72 DPI....It'll typically be 2272x1704 pixels with an image size of 80.15cm x 60.11cm - pretty huge for screen viewing but no good for commercial printing as for this it needs to be 300 DPI. So, in Photoshop (or whatever image editing program you use), take the tick out of the "resample image" box and where it says 72 pixels/inch, change this to 300 pixels/inch. You will see that the pixel dimensions stay the same - 2272x1704 (4MP) but the image size has now changed to 19.24cm x 14.43cm. You now have an image of approx 19x14cm at 300DPI. What you have done in effect is crammed 300 pixels into a square inch instead of the original 72 out of the camera.
Hope this helps.
Images from my 300d opened in elements via the adobe raw plugin are 240dpi, size 32.51cm x 21.67cm
If I then resize the image smaller the dpi increases proportionately and vice versa upwards.
Thanks everyone
will experiment with adobe photo shop
Cheers
for that, sounds like a sensible answer to me.
My best advice for DPI is to ignore it. It is only a piece of information stored in the file to tell applications interested in taking notice how to handle it. The DPI setting does not in any way effect the pixel size or quality of the image, it is simply a ratio that lets you translate the pixel size into physical units like inches or centimetres.
If you want to go online and order a 6x4" then pretty much everywhere you go will do so at 300dpi, and only at that resolution, which means a file of 1800x1200 pixels. And if you supply them with a 1800x1200 pixel file at 72dpi, you will still get a 300dpi 6x4" print.
It is only when you are printing something yourself and have a choice of dpi options that it is something you need to worry about, any other time it will be ignored.
Michael.
Jimmy_Lemon
04-01-2007, 20:54
if you supply them with a 1800x1200 pixel file at 72dpi, you will still get a 300dpi 6x4" print.
Erm? how will you?
The DPI setting does not in any way effect the pixel size or quality of the image
Sorry but that's just wrong! The DPI directly relates to the printable size and therefore quality of an image. If you have an image that is 800x600 pixels at 72 DPI and you print it at say A2 size, you will see every individual pixel with the naked eye. Trust me, I do this for a living!
Sorry but that's just wrong! The DPI directly relates to the printable size and therefore quality of an image. If you have an image that is 800x600 pixels at 72 DPI and you print it at say A2 size, you will see every individual pixel with the naked eye. Trust me, I do this for a living!
thanks for mentioning this, as i was of the impression 300dpi was just for when you are scanning photos to your PC, and i recently sent some files to photobox which i'm sure where 72dpi as i think photoshop does this by default, so i guess next time i will have to make sure i change the dpi to 300 manually as you have mentioned, can you set it in camera to produce in 300dpi then ?
Any good printers should change the DPI to 300 anyway before printing the file I would of thought.
I only shoot RAW and they come in natively as 300dpi with adobe cs2.
thanks for mentioning this, as i was of the impression 300dpi was just for when you are scanning photos to your PC, and i recently sent some files to photobox which i'm sure where 72dpi as i think photoshop does this by default, so i guess next time i will have to make sure i change the dpi to 300 manually as you have mentioned, can you set it in camera to produce in 300dpi then ?
I don't believe you can set a camera to produce a 300dpi image, although I'd happily stand corrected if someone knows of one that can :shrug:
The whole dpi and file size issue can be very confusing - I posted this earlier in this thread:
Lets take a 4MP image at 72 DPI....It'll typically be 2272x1704 pixels with an image size of 80.15cm x 60.11cm - pretty huge for screen viewing but no good for commercial printing as for this it needs to be 300 DPI. So, in Photoshop (or whatever image editing program you use), take the tick out of the "resample image" box and where it says 72 pixels/inch, change this to 300 pixels/inch. You will see that the pixel dimensions stay the same - 2272x1704 (4MP) but the image size has now changed to 19.24cm x 14.43cm. You now have an image of approx 19x14cm at 300DPI. What you have done in effect is crammed 300 pixels into a square inch instead of the original 72 out of the camera.
Just to add further - the image doesn't HAVE to be 300dpi to be printable commerically if the image is scaled. eg: in the above example, the printer could take the 80x60cm 72dpi image and print in at approx 25% reduction in size and achieve the same quality as if you scaled the image yourself in photoshop and actually made it 300dpi and the printer printed it at 100% size.
Ultimately it about getting 300 pixels into a square inch so if you do it in photoshop that's ideal because you are supplying an image for printing at the correct size and quality for printing.
I hope that helps :shrug:
DPI is all about printing blobs on a sheet of paper , it doesn't relate in anyway to what the camera has captured.
The camera records a finite number of pixels at whatever resolution/quality it has been designed for / set to.
When the user decides on the size of print is required then the post processing scales the camera image to match the printer resolution to give the desired finshed size.
Its all about fiddling numbers , the only bits that are real is the number of pixels on the sensor & the texture of the potato used for printing :D
My best advice for DPI is to ignore it. It is only a piece of information stored in the file to tell applications interested in taking notice how to handle it. The DPI setting does not in any way effect the pixel size or quality of the image, it is simply a ratio that lets you translate the pixel size into physical units like inches or centimetres.
If you want to go online and order a 6x4" then pretty much everywhere you go will do so at 300dpi, and only at that resolution, which means a file of 1800x1200 pixels. And if you supply them with a 1800x1200 pixel file at 72dpi, you will still get a 300dpi 6x4" print.
It is only when you are printing something yourself and have a choice of dpi options that it is something you need to worry about, any other time it will be ignored.
Michael.
which is pretty much how I understood it to be.
Sorry but that's just wrong! The DPI directly relates to the printable size and therefore quality of an image. If you have an image that is 800x600 pixels at 72 DPI and you print it at say A2 size, you will see every individual pixel with the naked eye. Trust me, I do this for a living!
Grendel - trying to understand more than doubting you.....
DPI = dots per inch. If a picture has 1800 dots (pixels) in width and you don't throw any away or create new ones by changing the number of dots in an editor, How does the quality change if the file info happens to say 'print at 72 dots preference set' or 'print at 300 dots preference set'.... and you then ignore it as mij posted. mij did state the same pixel dimensions for both.
Not sure I see the connection to your example of a small file printed too large.
For printing a 6"x4" at Photobox, as long as you upload an image more than 1800x1200, it will get resized/cropped to fit that dimension (aspect ratio 3:2) to fit in 6"x4". It doesn't matter if you have the DPI set to 70 or 300.
Of course it is better if you cropped/resized yourself so that you know exactly what you're getting.
I think the quality changes, Robert , because they will be printing at the same size of 6X4. If you have a finite number of dots in an image.. then if you squeeze those dots in to each inch at 300 dots in each inch...... then the quality will be good but you will run out of dots after only a few inches so the image will be small. If you use the same number of dots and onlly put 72 in each inch...you will be able to carry on into more inches as you will have more dots left over.
So, if you send in a photo at 72dpi for printing and ask for 6 x 4 they print at 300dpi so that will be ok
Alternatively, if you want the image to be bigger than 6X4 and only send it in as 72dpi they wont be able to change it into 300 dpi for printing as by the time they have put 300 of the dots into each inch...they will have run out of dots at 6X4 so wont be able to print bigger at that good quality. The only way to print bigger than 6X4 would be to stretch out the dots and have less in each inch....which would indeed show al lthe dots and result in poor quality.
HTH either that or it has set everyone into more confusion!
But a 72 or 300 'tag' in the file won't change the number of pixels in the digital image. So how can the quality change if you just ignore that number? The file will have (say) 1800 pixels across whatever the DPI print number is.
But a 72 or 300 'tag' in the file won't change the number of pixels in the digital image. So how can the quality change if you just ignore that number? The file will have (say) 1800 pixels across whatever the DPI print number is.
Because by changing the dpi from 72 to 300 you are compressing more of the pixels (aprox 4 times more) into the same area therefore improving the PRINTING resolution. The amount of pixels in the image doesn't change but the PRINTABLE size of the image reduces
You can increase the number of pixels in a square inch to improve print quality but if you go the other way, ie try to print a 72dpi A5 image at A3 you are actually putting 4 times less pixels into a square inch and therefore reducing the PRINTING quality
But a 72 or 300 'tag' in the file won't change the number of pixels in the digital image. So how can the quality change if you just ignore that number? The file will have (say) 1800 pixels across whatever the DPI print number is.
The quality can change because you are deciding to print at different sizes and therefore stretching out that finite number of pixels over a larger area...therefore the quality is poorer. Why are we tallking about ignoring the numbers? the numbers are important when you are printing. the tag of 72 or 300 isnt important when looking at your file size but it is when you are going to print and put those dots into each inch.
The file will have (say) 1800 pixels across whatever the DPI print number is.
you are right...the file will have 1800 across but the size of the printout and quality of the printout will not be the same whatver the dpi print number is.
any image has a given number of pixels (which I think is what you quite correctly are saying Robert), it's about how many of those pixels you put into a square inch of printable size that determins the final printing quality. If you look at a picture in a newspaper up close you can see the individual dots that are used in the printing process - this is because newspapers print at a very low resolution, typically 150dpi. Now look at a high quality print in a hardback book or similar. You will only see the individual dots if you use a magnifying glass this is because it will have been printed at a much higher resolution, typically 300 dpi. More dots in a square inch.
1000 x 1000 pixel image. I want a print 5 inches square.
If the dpi is pre set to 300 but I still print it at 5 inches square, surely the print program will arrange 200 pixels per inch and them resample them to suit the printers nozzles or whatever. So the dpi in the file is ignored.
Where is the flaw in my logic ?
Ok so the confusion is if a printer really does make 72 or 300 dots spaced apart and that is the best it can do?
I think it will print 200 an inch because of your filesize and the size of the print you are requesting.... and the dots may be noticeable. the printer wont manage to squash 300 dpi in there..if it did then the print would have to be less than 5X5
No flaw at all Robert. The maths is:
1000x1000 pixel image at 300dpi would actually print at 3.33x3.33 inches. If you wanted to print it at 5 inches x 5 inches the dpi would become 200dpi, therfore slightly less quality
I think it will print 200 an inch because of your filesize and the size of the print you are requesting.... and the dots may be noticeable. the printer wont manage to squash 300 dpi in there..if it did then the print would have to be less than 5X5
Or what Janice said! :thumbs:
Ok so the confusion is if a printer really does make 72 or 300 dots spaced apart and that is the best it can do?
Ah now you're getting into printer resolution, that's another subject altogether! :bang:
LOL.
Makes your head hurt don't it. PPI and DPI are two different things - the latter refers only to printer settings.
http://photo.net/learn/resize/
DPI only relates to printers & scanners. They have a true , physical capability. All the rest is smoke & mirrors.
After all if a 1800x1200 camera truly was 72dpi it would need a ******* big sensor :D
LOL.
PPI and DPI are two different things - the latter refers only to printer settings.
Good point CT :thumbs: ppi = pixels per inch, dpi = dots per inch
A lot of confusion comes in because people tend to use dpi as a generic term when refering to image resolution :bang:
The PRESET dpi isnt actually IN the image. It is just called that as a statement of the size and how the dots will be arranged in each inch. The output size and amount of dots are interlinked. SO if you decide to change your dpi then your output size will have to change.
You really just have a 2400 X 1800 pixel image. end of story. then if you are asked about the resoultion and you say it is 300dpi.(for print) that shows it can be printed out at say 8X10 and be good. if you said that your 2400X1800 image was at 72dpi and was to be printed out. people would know that either you were going to get a smaller image than 8X10 (using 300dpi to print with) OR that if you did indeed print at 72dpi and get the 8X10 size ...it was going to be very grainy and dotty.
Hope I'm not going round in circles, Robert, Im trying to help...truly I am! :thumbs:
Sorry but that's just wrong! The DPI directly relates to the printable size and therefore quality of an image. If you have an image that is 800x600 pixels at 72 DPI and you print it at say A2 size, you will see every individual pixel with the naked eye. Trust me, I do this for a living!
Precisely! The DPI relates to the printable size and does not affect the pixel size of image quality of the file.
An 1800x1200 pixel file is an 1800x1200 pixel file regardless of the DPI setting in the file. And when printed out by a printer that only offers 300dpi output it will give you a 6x4" print regardless of the DPI setting in the file.
The DPI setting is an instructional field in a text file that can be used or ignored, in the majority of cases it will be ignored.
I use non-destructive cropping which means setting a size of 3x2" in Photoshop and it calculates the DPI setting relative to the pixel size of the image. And when I send off an image like that, with a DPI value of over 900, to a lab that only prints at 300dpi I always get back 6x4" prints. No one one has ever sent me a really high quality 3x2" prints.
If you change the DPI setting in Photoshop the image will remain the same unless you resample it. The only difference between an 1800x1200 image at 72dpi and an 1800x1200 image at 300dpi are the bytes which record the DPI setting. The image itself remains identical.
My point is not that the concept of DPI has no meaning, but that in the majority of cases the DPI field within the image file is ignored, and when it does matter you will be told it does and what you need to use.
So unless you are printing yourself the DPI setting is something you do not need to worry about as the printer (human or software) will handle this based on their own particular requirements.
If anyone can name a non-specialist lab that offers user-customizable dpi settings then I would be interested, but I have never seen any that offer anything but 300dpi or 254dpi at larger sizes. And they will crop or resample as appropriate to get the appropriate pixel count before printing. Give them a true 72dpi 6x4" file at 432x288 and they will upsample it to an 1800x1200 file before printing, they will not print it at 72dpi.
Try sending them an 1800x1200 file set to 1dpi and see what you get back, it will not be a roll of wallpaper.
Going back to tomtom's original question, which seems to have been lost, it does not matter what DPI setting he uses in his software because when he sends his shots off to be printed they will be 99% likely to be printed at 300dpi and the only factor that will determine the quality of his prints will be the pixel size of the files.
One thing to remember, is that Photoshop was meant to be a printers tool, not a photographers one, which is why DPI and CYMK etc. are all prominent features. And this is why Adobe are producing LightRoom in response to the need of digital photography.
Michael.
Jonnyreb
05-01-2007, 10:38
Are we all happy now cos my head hurts ;)
neonpollen
05-01-2007, 11:04
Could you go through that lot one more time for me please :) :exit:
Are we all happy now cos my head hurts ;)
DPI - definition
Double Pint Intake
Time for a nice :beer:
:D
Are we all happy now cos my head hurts ;)
LOL mine too, very interesting thread though i have enjoyed reading it, but there was just one more thing :lol:
Jonnyreb
05-01-2007, 11:46
DPI - definition
Double Pint Intake
Time for a nice :beer:
:D
Sounds good to me - TFI Friday. Knew i should have taken this week off :baby:
I think TomTom might have quit the forums after starting this thread!! :D
COME BACK...it's ok..... I often start threads like this....usually about tripods!! :D :lol: ;)
I think TomTom might have quit the forums after starting this thread!! :D
I bet he doesn't realise what he started does he :lol:
COME BACK...it's ok..... I often start threads like this....usually about tripods!! :D :lol: ;)
and 486 computers :D
and 486 computers :D
:bonk:
Jonnyreb
05-01-2007, 12:56
Poor TomTom - thought a referee may have had to have been called in at one stage.
Nothing like a good debate:help: :gag: :cuckoo:
All intended in a friendly and helpful way though! I hope no one thought any of my posts were anything other than that. You've got me worried now :shrug:
No I dont think we meant that! Mine sounded a bit full-on as well.
We just meant that it got very deep and involved and tomtom only asked a little question!! :D
Jonnyreb
05-01-2007, 13:15
No I dont think we meant that! Mine sounded a bit full-on as well.
We just meant that it got very deep and involved and tomtom only asked a little question!! :D
Yep - my thoughts too. Nothing wrong with a good discussion and we got there in the end :)
Phew, just me being paranoid :embarrassed: :exit:
Phew, just me being paranoid :embarrassed: :exit:
Well,, actually........WE were having an in-depth discussion.....and YOU were going WELL over the top, Grendel!!!! ;) :nono:
Jonnyreb
05-01-2007, 13:54
Well,, actually........WE were having an in-depth discussion.....and YOU were going WELL over the top, Grendel!!!! ;) :nono:
Janice - mean lady!
Whats this about 486?:naughty: :whistling:
Yeah come on Janice, tell the man! :lol:
Grrrr well jokingly Steep said "I have a 486DX2 knocking about somewhere if thats any use to you" so I thought...funny isnt that a computer? So I sent him a PM to ask if a 486 dx2 wasnt a computer......only I sent the message to grendel instead and he didnt know what the hell I was talking about!!
He wouldnt be the first!! :shrug:
:lol:
But, being a gentleman I still replied as if I DID know what you were talking about :thinking: :D
:lol:
But, being a gentleman I still replied as if I DID know what you were talking about :thinking: :D
It had nothing to do with being a gentleman.....you just wanted to sound clever! :lol:
Jonnyreb
05-01-2007, 14:40
:lol:
But, being a gentleman I still replied as if I DID know what you were talking about :thinking: :D
:clap: the Gentlemanly thing to do.
Janice - the number of work related email cock-ups i've made stopped being funny a long time ago:embarrassed: I'm amazed they still pay me.
Roll on pub time :beer:
Just to add confussion, I scan all my Tx's at work @ 406dpi for our system :thinking: :lol:
It had nothing to do with being a gentleman.....you just wanted to sound clever! :lol:
:bang: bugger, rumbled again!
Roll on pub time :beer:
Here here :thumbs:
Just to add confussion, I scan all my Tx's at work @ 406dpi for our system :thinking: :lol:
SHUT UP!!!!! :D :lol: :D ;)
you love me really :love:
you love me really :love:
I would if you looked like Bruce Willis! :naughty: ;)
I do......kind of.......:cuckoo:
I do......kind of.......:cuckoo:
,,,in a funny sort of way!! ;)
Jonnyreb
05-01-2007, 15:22
Easy tigers - there's clearly something in the TP water today :geek:
Still got my hair though......
I think your aviator looks like the woman off eastenders....
Do you mean Ian Beale's wife..Jayne??? I have been likened to her before! :eek:
Or did you mean Dot Cotton?? :D :lol:
Cos if you did...........you might as well get your coat!!:exit:
thats the one.... Defo not dot, thats my mother-in-law (long standing joke)
Think we should start a look a like thread of *** on the forum, we must have some good uns out there....
I think your aviator looks like the woman off eastenders....
thought you meant jonnyreb :thinking:
thought you meant jonnyreb :thinking:
Well he'd have meant Mo Slater then!!! :D :D :D
Jonnyreb
05-01-2007, 15:45
Well he'd have meant Mo Slater then!!! :D :D :D
Hey - leave my little Moroccon chappy out of this. poor chap needed 10 mins in the shade at 8 in the morning.
Actually, after this week, i know how he feels :puke:
Sorry to chime in very late on this coversation guys but it seems like there's an aweful lot of confusion and bad advice here in relation to resolution. All seem to be talking about dots instead of pixels and there is a difference.
The truth is pixels are what images are made of. So in relation to resolution the term should be ppi (pixels per inch).
The resolution coming out of your camera matters not a jot until you come to printing. The only thing that matters is the number of pixels (as has been noted above). Some people seemed to think this was wrong but it is quite correct.
My 20D produces 3504x2336 pixel images. Whether it comes of my camera at 1ppi or 1000ppi the image is still a 3504 x 2336 image.
Now when it comes to printing there are a couple of very easy ways to work out the unknown variable like print sizes or resolution.
1. You know the size of print you want (say 10x8) and you want to print it at 300ppi. You would need an image of 3000pixels x 2400 pixels in order to do this. If you have more pixels you can print at a higher resolution or as many do is crop the image to the required pixel count. Quality from printing at higher than 300ppi is unlikely to be seen by the human eye so 300ppi seems to be the preferred quality for small images. You can actually print at around 240ppi without any noticable drop in quality in a small image like this and as noted below you can go a lot lower for large prints.
2. You know the number of pixels you have and you want to print a large 18" x 12" print. At what res will this print out at without resampling the image.
Resolution= pixels/print size so:
3504/18 = 194.666 or
2336/12 = 194.66
Contrary to popular belief, this will provide a high quality image that will look fantastic from normal viewing distance. Because viewing distance will be further than that of a 6x4, the ppi can be a lot lower for larger images. (look from a distance at a billboard then look close up and you'll see what I mean). By printing these larger images at 300ppi all you do is increase the image size (greatly) and at the normal viewing distance you will not see a difference in the print! I print my 19x13s at just under 180ppi.
You can also add a third equation to work out how many pixels you need for an image. If you want a 12x8 print at 300ppi you need 12x300=3600 and 8x300=
2400. So you need an image of 3600x2400 (just outside the normal range of an 8Mp camera.
Now with resampling switched on you can increase the pixel content of your image but because you can print even a 6x4 at around 240ppi without any noticeable drop in quality all you need to do is accept a slightly lower ppi setting.
I try not to resample too much because all you are doing is either adding information that is not there in the first place (adding pixels or upsampling) or deleting pixel information (downsampling). The only time I do this is if I require a very large print that takes my resolution below around 150ppi.
There's so much misinformation on this subject around the web it's amazing how anyone gets to grips with this stuff.
Printers print in dots (dpi) and my R2400 can print at about 5670dpi. Now no matter the pixel resolution of my image I can print it at this high setting. So my 72ppi file that is 6x4 will still print at 6x4 but my printer will print it at 5760dpi but it'll still look crap because the 72ppi is not a high enough image resolution to get a good print. dpi is only for printing and scanning and should not be confused with images which are made up of pixels not dots.
Does this make sense? Hope I can help those who are struggling to understand this. Your use of digital images will improve when you understand the basic concept.
Here's a pretty good link
http://www.steves-digicams.com/techcorner/January_2005.html
Cheers
Jim
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