ACTN003: Strange Filters: Clamping and Cropping.

In Acorn’s Filter menu you’ll find a couple of interesting filters that at first glance, look like they are pretty useless. I’m referring to the Clamp and Crop to Original Bounds filters.

You might from time to time use a filter that expands the the pixels of your layer beyond the original bounds (like a distortion filter). Or maybe the filter you’re using is pulling in pixels from outside the bounds (such as a blur filter). This is where the Clamp and Crop to Original Bounds filters will come in handy.

Here are some examples.

The above image shows a crop of a woman hanging off a rock. It has transparent pixels along the sides of it for the purposes of our example. There are no filters, and this is what our image would originally look like.

Next we have our same image with a Motion Blur filter applied to it with a Radius of 100px. You’ll notice that the image now bleeds into the transparent areas, as the motion blur smears the image beyond the original bounds. You’ll also see that the transparent areas bleed into the previously opaque areas of the image. The blurring goes both ways.

Now we’ve added a Clamp filter before the motion blur. The Clamp filter puts a “box” around the edge of our image so any filters that try and grab pixels outside of the frame of our image, they won’t grab transparent pixels but instead grab the last pixel on the edge. See below for what a Clamp filter looks like without any other filters.

This is what your image would look like with only the Clamp filter applied.

Next we have a filter with Clamp, Motion Blur, and finally a Crop to Original Bounds filter. You’ll notice that the edges of the layer are no longer smeared or pull in transparent areas. This is because we’ve cropped our image back to the original dimensions that our layer started with.

This is an example of the Glass Distortion filter with the Crop to Original Bounds filter added after it. You’ll notice that the edges are a little rough. This is because the Glass Distortion filter is pulling in transparent areas from outside the original layer.

Finally we have an example of the same Glass Distortion filter, but this time with a Clamp filter applied first. We no longer have the transparent areas showing up in the filtered image.

Clamping isn’t working?

Your layer might contain transparent pixels as part of its base image. Try using the “Trim Layer to Opaque Bounds” Command Bar action to trim up any transparent pixels.