How to tell DPI ?

broadsheet

Can anyone tell me how I can tell the DPI of an image. For example, an image on google images give the size underneath but how can I tell the dpi keeping in mind I dont have any graphics software.

Ruu_Old

Right click on the image, then Properties, click the Summary tab and then Advanced. I think it should show you there.

broadsheet

Ruu normally only a general tab comes up and it doesnt give the dpi details.

Blisterman

dpi is usually only used for printing, in which case, it depends on your printer.
It might be pixels you're looking for.

Citizen_Erased

broadsheet wrote:

Ruu normally only a general tab comes up and it doesnt give the dpi details.

You have to save the image to your hard drive then right click the file it self and do as Ruu said (well thats how it works for me in Firefox , dunno bout IE)

nialler

If you have no graphics program here's the free version of photoshop was developed on unix but ported over for every OS.

http://www.gimp.org/

(stands for graphic image manipulation program) don't laff.

mathias

Heres some info relating the pixel count per image to PPI ( pixels per inch ) and DPI ( dots per inch ).

http://www.cambridgeincolour.com/tutorials/digital-camera-pixel.htm

Top quality is generally considered to be 300DPI but you can get away with a lot less , there is a chart that shows relative print size for megapixel count and quality.

Very roughly , you can equate pixels to dots , so this means that a 900 by 900 picture will only give you a 3 inch by 3 inch print at 300 DPI , and so on , so print size for a given quality can be worked out from there.

broadsheet

Thanks guys, didnt think there was as much to it. Its for a billboard image Im helping someone design. The booking company told us that the image must be 300 dpi. On stock photography they all clearly state the dpi but on images elsewhere I couldnt see the dpi. Also can you tell me if the dpi is 300 as required will the image reproduce to billboard size without losing quality or do I have to look for a specific size like 2000 x 1500 like I see on google images.

Thanks guys

sdssarah

You'd want to be careful, it sounds like you're looking to get an image from google and then use it commercially, which is a breach of copyright. So you should stick to stock photography, or photograhpers, whom you can pay (royalty-free are the best as it's a one off payment rather than payment every single time you use the photo). You can't just use an image somebody has taken that you find on the internet as you have no rights to.

And using a 300DPI image for a billboard is usually fine. Due to billboards being so large they don't need have perfectly crisp images on them, as most people will see them from far away, so they tend to be a little pixelatted, but this doesn't affect the visual of the billboard if you understand me.

broadsheet

I can assure you that I wont be nicking an image from anywhere I just used the google images as an example of where I can see the size but not the dpi.

Thanks for the input.

Citizen_Erased

Sorry but can i just do bit of math here , a three hundred dot per inch image that would need to occupy the size of a billboard which I will guesstimate at 15ft by 10ft or whatever then would that not mean an image of resolution of roughly 54,000 by 36,000 ?Isn't that impossibly huge , should a bill board not be at like 40 or 50 so dpi or less, you know the sorta thing that wouldn't make sense if you put your head 2 foot from it, more like pop art. Or have i completely missed the point alltogether here as I have a very limited comprehension of dpi (I don't even own a printer, lol )

tba

Usually billboard images are blown up from a smaller image , and thus their DPI reduces, you are correct they have a final dpi of 2 to 20, and the dots are clearly visible.

spidermonkey

what you will need:
a piece of paper
a pencil
an eraser
a ruler
a looking glass
a calculator, if you do not have or own a calculating machine, you may also use an abacus

step 1.
using your looking glass hold it at a comfortable distance from the page.
you will notice tiny dots that make up the image, regular people don't know this, but dots make up everything in our world, as designers we are privileged, we hold knowledge beyond our years.
then using your looking glass proceed to count from left to right ever dot on that line and at the end of each line write your result on your piece of paper.

step 2.
now return to your image and move down
to the next line and repeat step one.

step 3.
when you have counted all the dots, using your trusty calculator proceed to add up your results and calculate your results using your trusty calculator. keep note of your answer, preferably write it down.

step 4.
using your ruler, in inches (as it is the standard for this measurement), proceed to measure your image from left to right and top to bottom, when you have your answers keep note of them, ideally, write them down.

step 5.
now using your trusty calculator proceed to divide your answers into each other to get your DPI (DOTS PER INCH) result.


learning outcome:
by doing this exercise many times you may become proficient in naturally knowing the final result of an image
and as such can say phrases such as "ahh, that must be 72dpi as it is much easier to see those dots"
or "ooooh thats 300dpi, that shall do nicely for print"

class has ended,
you may leave

Dundalk Daily

so back to the thread, how can i tell the dpi of an image ???

Dundalk Daily

Logged in wifes account above.

Dundalk Daily

Also does royalty free mean its free to use, free from copyright ?

spidermonkey

royalty free means that once you purchase the image its free for you to use as often as you like without paying to use it each time.
it doesn't mean you can take the image and use it for free.

generally speaking if you take something from the net it will be 72 dpi,
if you buy hi res imagery online or from some other source, it will still show up as being 72dpi anyway, but its size will be massive, so before going to
print you must up the dpi in photoshop to 300,

in photoshop go to 'image->image size' and then you will notice the dpi, change this to 300, but dont check the box to have it resample the image
if you check this box it will add the extra pixels but also enlarge your image so it will still be 72 pixels per inch, when you uncheck it it adds the extra pixels required for print but doesn't enlarge the image, so you have 300pixels per inch

screen grabs below

before:


after:


hope that clears up the topic for you.

sdssarah

Royalty free means you can use the image multiple times for one price, but you don't own the copyright on it.