You can create a curved, “lifted” shadow effect for web page elements by using PhotoShop to generate image that will be applied to the element with CSS. As a pixel-based image, a primary goal of process is to keep the shadow as small, light, and responsive as possible.

If you are executing the same simple sequence of operations in PhotoShop on two or three images, it’s usually fastest to do so manually. But the moment that you repeat the steps more than a few times, it is easiest to record the operation as an automated process.

Applying an automated sequence of operations to a set of images is known as “batch processing”.  Batch processing is typically used to create a series of thumbnails for a gallery, or interchangeable banner images, or headshots for the profile page of a board of directors. In this tutorial we’re using the first example, but in all cases, the final images need to be the same size and aspect ratio. I’ll be using images from 500px.com, my newest favourite photography site: the photographs are by Mike Orbinski, Dale Martin, and Tom Lowe.

For a real-world example, you would want your source images to be as high a resolution as possible, and in a lossless format, in order to preserve the highest quality possible during our workflow.

In PhotoShop we wish to execute two steps:

If you look at the clouds PNG image we made in the last exercise, you may be surprised: you’ll likely find that its file size is somewhere north of 45K. When we are trying to make pages that are under 60k – including images, content and code – that is too high.

You’ll also recall that PhotoShop insisted that we save the image in PNG-24 format in order to preserve the alpha mask. That is the first lie that PhotoShop told you; the image is actually a PNG-32: 24 bits for color and 8 levels of grey for the alpha mask.

But that’s ridiculous, you might respond. I’m actually only using one color – white – in the entire image. Everything else is the alpha mask. Surely I’m wasting a lot of space trying to make room for 16 million colours that I’m not actually using?

Yes, you are.

So if I’m only using one actual color, I should be able to cut the color depth down to 8 bits or less and save some space, right?

Not in PhotoShop: it only recognizes two formats: PNG-8 with an optional single transparent color, or PNG-24, with an optional alpha mask.

Aaaargh!

Indeed.

Thankfully, there is a solution: Fireworks.