photography (again!)

passionatepens

Hi all,

This is for the photographers amongst you.

Ive noticed that most magazines want 'digital 300 dpi images'. I know this is 300 dots per inch, but how do I know if thats what my photos are - or how can I change them if need be?

Thanks, and apologies for the vagueness of the question - I dont really know what Im talking about!

Christine

boredrobots

If they are on the computer, right click > Properties > Summary tab

That will tell you :)

dorothyd

if you are using Photoshop or something like that, you will find that information if you click on Image size.

Mabh

Yeah, but...

If something is 3600 pixels wide and 180dpi, does that not mean that if it was printed at half the size, it would be 360dpi?

Carol

Actually I've always wondered how you get it to 300dpi too.

Liz

If something is 300 dpi, it'll still be 300 dpi even if it's only half an each wide... it's the quality of the image. Like if a piece of sheet of Egyptian cotton had 300 threads per inch, it would still have 300 threads per inch even if it was a half inch piece. Likewise if it was 10 inches across, it would still be 300 threads per inch.

Carol

So if your photo has more dpi than 300, can you reduce the dpi?

Mabh

Aargh. I think I may have to buy Photoshop - when I used to design catalogues, I could check all this stuff, and now I'm trying to do this with the seven different types of photo opening software I now have between the new pc and the camera, and not one of them answers this one so simply!

What has really been getting my goat is that when I re-size using one of these non-photoshop programmes, it's still 180dpi - what's it done with the rest of the pixels? I'm sure if I sent them to a designer to print he'd sort it in a jiffy but I want to do it myself! I'm thinking I should be ok as apparently my pictures are coming out at 20 inches wide (at 180dpi)... but how do I squash them pixels into 300 dpi, she said, starting to ramble pointlessly.

Put me out of my misery, someone!

dorothyd

Mabh, my partner made the mistake (as posted above) of thinking if he squashed the image he would squash the size. Someone had to point out to him that they were taking up just as much space whichever size he used, if he didn't reduce the pixels in Photoshop first. Now we reduce everything to 72 or thereabouts so it takes up less room.

(He had a hard drive crash today ... he is not a happy bunny!)

Mabh

Ah, what I'm trying to do is halve the size in inches to double the pixels per inch. This would mean that the digital file would take up same amount of memory space, as you say, but it would also be high res for printing.

Unless I've completely forgotten how this works.

dorothyd

I am not sure the size regulates the amount of pixels. I could be entirely wrong here, though.

Liz

Ok, so if I had a drawing with 48 dots in it, over 4 inches square, it would have 12 dots per inch. If I make it a 2 inch square the dots don't become less numerous, they are the same distance apart, therefore the same quality, ie 12 dots per inch.

So changing the SIZE of the picture does nothing to change the dots per inch.

You need to get rid of some of those dots. Your computer should be able to... on my mac I just ask it to reduce the quality to say 72 dpi. You can do the same on photoshop.

Mabh

Hmm. I actually think that it should be possible to halve a print in inches to get twice the pixels. Maybe you have to do it in photoshop, though, not the software that comes with the camera.

I think the word is interpolation.

Liz

Ooooer! Dpi of course is a printer term and they are really pixels. Can you do a computer search and ask how to do it? Or PCs not do that?

mcbemused

Hi PP - if you have a pc and windows picture viewer, open the picture, click file, then properties, then summary - this will tell you the density of your picture (which in this case is what you need to know).

It is possible to change the density of a picture, but you would need some sort of picture editing software for this - photoshop if you have it, but just about any other will do (a good basic one is iPhoto Plus). You can alter the density of the picture under the resizing tab - but remember, it is density you are looking to change, not the size of the picture (as in 10 x 8 inch etc.)

Mabh

Thanks Mcb, I thought that was the case but four years on from when I was fully tooled up with fancy macs and software, I find I've forgotten stuff. The editing software that came with my camera does not appear to allow me to upgrade the dpi - when you change the size, it keeps the original dpi. No mention of densitys and interpolation.

Funny thing when you go freelance - you don't realise how lucky employed people are to have good quality facilities including brand spanking new copies of photoshop!

Jediya

Also check your camera's manual Mabh - you might be able to pre-set the dpi/ppi to 300 on the actual camera. This will save you having to use a program to increase it.

Edited to add: Of course, that's only relevant or works if you're shooting RAW.

Nena

In Photoshop, if you go to image size and change 'resolution' from eg 72dpi to 300dpi, it will in fact make your picture a whole lot smaller. I just resized one that was 17 x 13cm and when I changed it to 300dpi, it shrank to around 4x3cm.

passionatepens

Thanks all - lots of help there :-)

pp x

Mabh

[quote=Nena]In Photoshop, if you go to image size and change 'resolution' from eg 72dpi to 300dpi, it will in fact make your picture a whole lot smaller[/quote]

Yes, that's what I thought. Which probably explains why my camera is producing 20 x 15in prints at 180dpi! - plenty of room to be shrunk and still be a full page size.

Jediya, you are quite right, I should read my manual. I confess I was so excited to get the thing that I just charged outside and started pressing buttons ;)