Changing resolution of images for printing

k.simmonds

I have just started producing photo books, and I am very pleased with the results. But then I realised that I should have changed the resolution of the images I sent to the printing company from 72 dpi to 300 dpi. I have just sent another book with all the images changed to 300dpi which should be good. But ..... I didn't do anything with the "resampling" tick box - I just left it ticked (mainly cos I didn't understand it). Should I have unchecked the "resampling" tick box ?????

Matt · VIP

Hey k.simmonds,

Photoshop handles resizing (changing the print size) and resampling (changing the amount of pixels in the image) as two different things. As you wanted to change the resolution of the image, which directly effects print size, then you really want to turn resampling off.

The best way of understanding is to see it happen. Open the image size dialogue box and turn off resampling. Now everytime you amend the resolution you're changing the print size (because you're packing more pixels into each square inch of the printed page). Now if you turn resampling on, each time you amend the resolution you're going to see the pixel dimensions of the image change. That's because Photoshop is resampling the pixels.

I hope this makes sense, let me know if you need any more info.

k.simmonds · Posted: Sun Mar 16, 2008 8:14 am Post subject:

Thanks for the reply. I "sort of" understand. But if you don't mind sparing a few moments ..... Lets say the original photo that I want to send to the printing company is as follows:

2592 pixels
1944 pixels
91.44 cm
68.58 cm
72 pixels/inch

When I turn off the resampling, and change the resolution to 300, the document size goes down to

21.95 cm
16.46 cm

This is smaller than the 10" x 8" pages of the book I'm printing. Now what do I do ?????

Nice tutorials by the way.

Matt · VIP

Thanks, I appreciate it!

The problem here is that you haven't got enough pixels to work with. My advice would be to change the resolution to a value that gives you a document size that you're after, this may leave you with a slightly low-resolution print but in my opinion it's better than resampling to create new pixels out of nothing.

When you upsample a image, all Photoshop does is estimate what the 'missing' pixels should look like based on an average of the pixels that are there. This results in a loss of clarity and sharpness and is something I never do, especially when outputting to a commercial printer. If you feel like it's something you want to try then I'd recommend the 'bicubic sharper' interpolation method, that's about as good as it gets.

An exception to problematic upsampling is when you're working with vector objects such as text and shape layers - because these are mathematically determined you can upsample and downsample as much as you like without ever losing quality!

I'm just thinking also, is there any way you can reproduce the file you're working with? Maybe an option if the source material is larger that the version you're working with?

Let me know if you need any more help

k.simmonds · Posted: Sun Mar 16, 2008 10:24 am Post subject:

I get you. So if I turn off resampling, and change the resolution to 250, that gives me as near as damn it 10" x 8". Is that what you mean?

The book I have just produced with the resampling on, should be back from the printers this week. I was hoping for great things ...... but now I'm expecting disappointment. Still, you learn as you go on I suppose.

Matt · VIP

Exactly. To be honest, a resolution of 250ppi isn't that bad for printing. I know of some print houses that output at 267ppi.
I'd say that's good news because it also means that you only upsampled by 50ppi, so not too much of an issue. Hopefully your files will still look good.

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