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Keepin’ it Proportional

Posted By On May 7, 2005 @ 12:52 PM In Digital Photography | No Comments

Have you ever noticed when you resize a photo, there’s usually an option to “constrain proportions”? When you uncheck that option, you can plop in any height and width dimensions you please. With constrain proportions checked, changing one dimension changes the other. So what’s with all the proportion constraining? Read on.

Although the term Constrain Proportions sounds like something used in a medieval torture chamber, it’s actually pretty simple.

When you shoot an image with your digital camera, it’s taken within the aspect ratio of that camera (usually 4:3 or 3:2). For instance, my camera shoots an image that’s 3504 x 2336 – a rectangle that’s fairly proportional to a 35mm negative (a 3:2 aspect ratio).

Now, when I go to resize this, I need to keep the image “proportional” or it’ll look distorted. When I take pixels away from one dimension (say the width), I need to take a proportional amount away from the other dimension (the height). If I don’t it will look elongated or squished, depending on how I change the width and height numbers. Constrain Proportions does this automatically.

This is easier to demonstrate with an example:

Here’s the original photo. I’ve reduced it for the newsletter and kept the “Constrain Proportions” checkbox checked:

This time, I unchecked the box and just put in a pixel size of 400 x 400. Photoshop interpolated and squished the image into this (yuck-ola):

Now, if you find that you need, say a 5×7, but when you resize the image with “Constrain Proportions” selected, you get something like 5 x 7.5, you’ll know it’s because the aspect ratio of a 5×7 doesn’t match your image ratio. Not to worry though, Steve to the rescue :-)

All you need to do is a little cropping to make the photo proportional. In this case, crop off the top and bottom of the 5×7 (assuming a vertical photo, otherwise it’d be a 7×5 and you’d hack a little off the sides).

If you’re trying an 8×10, you’ll find you may need to crop even more in order for it to work. Again, off the top and bottom if the photo is vertical, from the sides if it’s a horizontal shot (10×8).

As you go, crop just a little at a time. Try the resize and see if you’re close (within like 5% or so). If you’re not, cancel each resize until you are. Don’t actually do the resize until you see that you have the proper proportions. It doesn’t have to be 100% perfect, but get it as close as you can. Also, always keep a copy of your original uncropped photo, just in case you want to make a different sized photo with different proportions down the road.

As an example of all this, let’s say I wanted the sample image to really be a square that’s 400 x 400. Here is the image after a correct crop (I cropped in a little too):

No distortion :-)

What do you do if you have a photo you just can’t crop? Don’t print it :-)

Or…

The first option is to allow it to print at the “strange” size. If it wants to be a 5 x 7.5, who are we to argue? If you’re having it custom framed, it doesn’t really matter what size it is.

If you can’t crop it and you have to have a standard size, there’s still hope (at least for users who are a little more advanced). You can create an image with just a black background that’s proportional to the size you want (like 5×7). Make sure it is at the same resolution as your original.

Next, resize the original so that the height is 7 inches. This will make the width 4.6 (ish).

Now, drop the photo onto the black background you created. Center it up and you’ll have a 5×7 with a black strip down either side, but at least it is proportional and will fit into a standard frame.

Here is our sample photo proportional to 7×5. No cropping of the image, but you have to live with the borders:

Of course, if you prefer a white background, you can do that too. Just set the height to 7 inches, let the width go to 4.6 inches, and print. Now, cut the image down to 5×7, leaving a white border on either side.

There you have it—more than you ever wanted to know about constraining proportions and working with aspect ratios :-)

Happy shooting!

~ Steve


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