Expert: Scott Valentine - 10/25/2007

Question
Hello, I am an artist and the galleries I submit my work to are now asking for CDs instead of slides. I need to send out my images the following way, 300 dpi measure no smaller than 8" (2400 pixels) no larger than (4900 pixels)
I shoot my work in jpg form and high resolution I use CS3 but can not figure out what they want. How do I do this
Please Help
Thank You Frank Hoeffler

Answer
Thanks for your question, Frank. Many galleries and stock agencies insist on high quality digital files, so this is not unreasonable. There are a couple of ways to get there, so you'll have to find the method that works for you.

First, you can check to see if your camera can shoot TIFF or RAW images at the required resolution. If so, then you're set. In any case, I do recommend shooting in TIFF or RAW as a matter of course, if your camera supports these formats. If you shoot in RAW format, then Photoshop's RAW processor will allow you to interpolate up to the desired size with no problem whatsoever. Check the help files in CS3 to learn the specifics.

A more practical option may be software like Alien Skin's Blow Up software:

http://www.alienskin.com/blowup/index.html

This software helps you increase the size of your images with little to no loss in apparent quality or resolution. It gets great reviews, but I've not had an opportunity to try it. The advantage is you have many settings to adjust so your images come out right, and you can make up to 1600% increases (4 times the area).

If you have to make the changes manually in Photoshop, you need to spend some time figuring out what looks best for your photos. In Photoshop, go to Image > Image Size and take a look at the dialog settings. Notice there is a section for Pixel Dimensions and Document Size.

The first one determines the size of the file in pixel dimensions. If you type in 2400 for the smaller dimension, you'll notice that the Document Size changes, but Resolution stays the same (probably 72 unless you changed it previously). If you now change the DPI to 300, the Document Size begins to look right, but now the Pixel Dimensions goes way up.

Down at the bottom of the box you should see three check boxes: Scale Styles, Constrain Proportions, and Resample. Turning off Resample restricts changes to the Document size portion. Changing the size influences the DPI, and vice verse. Leave Resample checked, and select Bicubic as the method.

Starting from your original dimensions (hold ALT/OPT and the Cancel button becomes a Reset button - do this if you need to start over), change the DPI to 300. If your smallest pixel dimension is not 2400, you can either change it directly, or begin increasing in small increments. I suggest the later, using 10% increases and repeating the process until you get the size you need.

This can be very effective, but causes your image to be interpolated. That means Photoshop takes two pixels that are next to eachother, moves them some distance apart, and makes up the information in between. In the end, this hurts image quality, but it may not be noticeable if you don't have far to go, or if the image has a lot of detail to begin with. Your image may end up with artifacts and unsharp areas.

Alien Skin avoids this problem with some advanced interpolation algorithms that make decisions based on fractal methods. If that sounds complex, it is. Just take away that it does its job very well.

I hope this helps. Please let me know if you need further assistance!

-Scott