Resolution question: 72dpi?

[Jonas]

I've just started using Photoshop 6 to PP my photos and one thing I noticed when looking at the 'image size' pane is that the resolution is set to 72 dpi.

I've tried to change it to 300dpi but it takes ages and I end up shutting the program down. I want to print a lot of my photos and I'm thinking 72dpi is not good enough.

I did notice that when I used the marquee tool to crop to a 6x4 or 5x7 and then changed the res to 300dpi, there was no problems.

My question is: should I just work on the image at 72dpi and if I decide I want to print it out, use the marquee tool to change to the right size and change the res at the end of the process?

I am shooting in Fine JPEG and uploading to Picture Project.

[losfp]

I don't usually worry about the print settings as I tend to just burn images to cd to get printed at a photo printing place (I work in web, not print.. so I think in terms of pixels, not dpi).. but the times I've wanted to print at home, this is what I would do.

Set the dpi value first (say, 300).
Then set the print size - that will adjust the resolution to the appropriate sizes.

I usually prefer to do my PP in the intended resolution, or at worst, a larger size so I can resize smaller.

[MattC]

Jonas,

It sounds like you are using the crop tool which crops and resizes. My preferred choice is to crop without resizing using the marque tool and resize later using >Image>Resize Image. This will probably get you around the sluggish response that you are experiencing. BTW, how is the situation with memory?

Here is a thread on the subject... Hope it helps
http://www.dslrusers.com/viewtopic.php? ... ht=#103851
There are a few more around like it.

If you can print at a value of say 240dpi or more you'll be laughing. Required dpi also varies with viewing distance - up close (less than arms length) more is better but something like a billboard viewed at 100s of metres can get away with dots 6" or so in diameter.

Cheers

[mikephotog]

Try using 200 dpi rather than 300dpi.
The difference would be negligible, if evident at all.

[Nnnnsic]

Indeed.
200dpi is what most print houses will use, 300 is what most camera and printer salesman think you need.

200 is the lowest you really go if you're printing A4 to A3, however, once you get into the A1-A0's and higher, 72 is usually fine.

[paulvdb1]

Jonas - noted that with my dad's P&S that the camera sets the image resolution to 72dpi. My D70S sets the image resolution to 300dpi

You basically just resize, set to 300dpi and change the pixels back to their original number. What you are doing in changing from 72dpi to 300dpi is blowing up the image size by about 16 - hence the reason your computer is committing suicide.

Does anyone know for certain what DPI a normal image lab machine prints at? If it's 200 DPI then I can shrink my 6*4 images further and cram them on one of my small CF cards.

[MattC]

Oh yeah, to answer the actual question...

My question is: should I just work on the image at 72dpi and if I decide I want to print it out, use the marquee tool to change to the right size and change the res at the end of the process?

Yes to the first bit. It does not matter what dpi you edit the image at. In PS you are dealing with a fixed number of pixels. DPI only really matters when you send the image to the printer where print size (and therefore resolution) needs to be defined.

For the last bit. I would use Image>Image Size to adjust for printing. Personal choice... but for a reason - sometimes I simply do not know what the final print size is going to be.

So adjust image, crop (without resizing) etc, then if you decide to print, resize, sharpen and print.

Cheers

[Jonas]

Thanks Matt, I did read that link before and so have started using the marque tool to avoid the resizing issues.

Another problem is my laptop. Its an IBM bought in 2001 with 550Mz and whatever memory was available in those days - probably not a lot!

Not quite sure how to get around the fact it can't cope with working in 300dpi. As mentioned before, I might just have to work in 72 dpi and crop (using the marque tool) to 6x4 or whatever and bump up the resolution to 200 or 300 when I want to print them.

I assume there will be some loss of quality but hopefully not as much as I have had when printing (mistakenly) in 72dpi.

[Jonas]

Oops, a few more posts were made while I was writing my reply (above). That makes a lot more sense now, many thanks for your near instant replies.

[sirhc55]

In the real print world the meaning of dpi is always translated to lpi. If you are printing litho at 150lpi the photo should be 300dpi and no less than 240dpi.

If printing at 175lpi the dpi should be 350.

For newsprint that has anything from 75lpi and up one should use 150dpi or more.

[oli]

On a related note I'm a bit confused about why 72 dpi is still seen as a "relevant" figure. Anyone with a 17" LCD or a high resolution screen will have a resolution closer to 110dpi (the way I calculate it) than 72dpi.

ACR with images from my 350D seems to have a default dpi of 240.

[Nnnnsic]

72 has two forms of relevancy I can think of off the top of my head:

1. Web size is 72 dpi.

2. When printing at around A1 or larger (metre prints and such), you tend to send out at 72 as no one will ever get close enough to an image of that size to care.

[oli]

72 has two forms of relevancy I can think of off the top of my head:

1. Web size is 72 dpi.

2. When printing at around A1 or larger (metre prints and such), you tend to send out at 72 as no one will ever get close enough to an image of that size to care.

The "web size" has come about because on older lower resolution screens 72dpi was about realistic, these days I doubt many people are running their screens at a resolution where 72dpi is accurate.

Fair enough about the second, but how that became a standard when the average person (in my experience) is printing <A4 is a bit strange.

[Nnnnsic]

It's not so much a standard but rather comes down to two f the factors regarding quite large prints.

Those two factors are:

1. The previously mentioned "no one will ever get that close to it" rule because once you are that close, you're no longer taking the image in but are rather looking for pixels, and the only time one really needs to do that is in a darkroom when you look for grain to see if the image is in focus. Images printed from an image are generally always in focus in regards to pixel / grain amount and don't suffer from possible OOF prints that a darkroom print will give you.

2. At around 300dpi, a 20x24 image will be around 100mb - 300mb... and that's not even A2.
So we lower the size of the image down to 72dpi because that means there's less data to feed to the printer and less time the printer has to take to look at the image so it can start printing it already.
It will still take a good while to print, but it means the filesize is a hell of a lot smaller and when you're talking about devices that travel along 10/100 or USB (with it's oh so nice theoretical speeds it rarely reaches), the speed of printing an image of that size will become a major issue, especially if you're a print house.

Furthermore, for setups like Lambda (I think Vutek and Pegasus are quite similar too, among others) when it's essentially a colour darkroom hooked up to a computer, you find that it's a combination of both points one and two.
The compact (in a sense) darkroom is already pre-focused and you'l lbe taking the image in at a distance and you want the device to get the image as quickly as possible for it to print in that sense so you can get the next job done.