The Lowly Transparent Shim

transparentshim
You probably read this post title and thought, “Shim? What’s that? And why is it transparent?” Well, in the days before CSS padding and margins, transparent shims were a godsend to webdesigners…but they can still help out our modern pages! Read on to find out how!

A Little Shim History

Transparent shims borrow their name from their wooden companions in the carpentry and construction businesses. These thin wooden pieces, often made from scrap wood or plywood, can be used to fill awkward gaps or spaces, help separate a couple of pieces of material, or make something fit more snugly and more level.

In webdesign circa the mid-2000s, a “transparent shim” image was about the only way to precisely position elements on your page. For instance, need an extra 30 pixels of horizontal space between your HTML form’s label and its text entry box? Then you’d just put in a little image tag linking to your shim image between the form label and text entry box, like so:

<img src=”shim.gif” width=”30″ height=”1″>

Or, if you needed more vertical space between your header image and your content, you’d put a little image tag like this between header and content:

<img src=”shim.gif” width=”1″ height=”50″>

Because this image was transparent, it could be stretched to any dimensions using the width and height measurements without the layout looking strangely colored. And, because it started out as a 1px-by-1px GIF file, it loaded quickly and didn’t clutter up slower connections.

These Days: Less Shim, More Padding

With the advent of easier-to-code CSS padding and margins, however, transparent shims have been less and less needed. No more need to call for that shim 50 or 60 times in a page when a couple of well-coded properties in a stylesheet can handle it all, right?

…Well, MOSTLY. There are a couple of instances where transparent shims can still help out:

Shim Situation #1: CSS Padding Rendering Differently Between Browsers

Sometimes Internet Explorer, Firefox, and Chrome will disagree on how to interpret CSS style rules such as “margin: 3px;” or “padding: 1px 10px 1px 10px;”. (CSS box model problems with IE, specifically, have been widely documented for several years.)

Shim Situation #2: Disobedient Layout Elements

Sometimes, an element on the page just will NOT position itself where you want it, and no amount of finagling, debugging, pleading, or shaking your fist at the screen will fix it. Whether text isn’t wrapping like it should, or whether some floated element is somehow “un-floating” itself, display bugs can ruin your webdesign day.

Enter the transparent shim; they act as little peacemakers, going across platforms, being equally accessible and understandable. All you have to do is put in that little image tag wherever you need it, and work with the pixel measurements to your heart’s content.

How to Make a Transparent Shim

  1. First, open an image program that can make images as well as edit them, and that can make images transparent. Adobe Photoshop Elements is the program I use; Microsoft Paint won’t do it, and neither will most really basic photo editors. Free applications that can make transparent images include GIMP and Pixlr.
  2. Choose to create a new image rather than edit an existing one, and make sure its width and height are both 1 pixel. Also, choose the “Transparent Background” option (could be in a dropdown list or a checkbox).
  3. Once you’ve created the image, save it as a transparent GIF or PNG-24 file. (JPEG format doesn’t recognize transparency.) Make sure you click the option to save it as a transparent file, otherwise it will just render as white. (For instance, Photoshop Elements has the “Save for Web…” option, in which you click a little checkbox reading “Transparency” underneath the file format option box. Your image program may be different–check every option before you click “Save!”)
  4. You should be done! To test transparency, load your new image, sized at 50 pixels by 50 pixels, on a basic black-background web page. If no 50×50 white block shows up at the top left corner, your image is indeed transparent!

Summary

Transparent shims are relatively easy to make and work with. If you have an awkward form width, an odd spacing, or even a fairly okay layout that needs just a little adjustment, try placing a shim, and see how heroic 1px by 1px images can be!

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