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GPU Acceleration: A Killer Reason to Upgrade to CS4

Upgrading versions of Photoshop isn't cheap and some people may be wondering whether skipping a release might be a good way to save money. If you've been trying to decide whether to spring for the CS4 upgrade I'd advise you to carefully review the new features on Adobe's website. But one new feature that is hard to fully appreciate without seeing it in action is the use GPU and OpenGL acceleration to speed up screen redraws.

I hear some of you asking just what a GPU is. That's understandable. It used to be that Photoshop wasn't very taxing on your video card. While the rest of the world moved into 3-D gaming that benefitted from the latest in graphics technology, Photoshop remained in the 2-D world. There was little need to get a high end video card for Photoshop work. But the world of graphics cards has continued to advance in spite of Photoshop. A GPU is a Graphics Processing Unit and is somewhat similar to your computer's CPU, or Central Processing Unit. As its name implies though, a GPU is dedicated to calculations involving graphics. This is the brains of your graphics card.

OpenGL is a cross-platform software library that serves as a means of telling your graphics card's GPU what it is working with and how to manipulate it. In other words, it describes objects and how to move them around in the space represented by your display. Rather than forcing your regular CPU to recalculate everything from scratch as your display changes, OpenGL allows your computer to offload much of the work to your GPU.

Every graphics card has a GPU, but some are smarter than others and support various "accelerations" to speed up common operations such as scaling or rotating objects. Even if your graphics card had a high-end GPU, Photoshop didn't really leverage it much up through the CS3 version. All that changed with the release of Photoshop CS4. Perhaps spurred by the addition of 3-D features in the CS4 Extended Edition , or merely from the realization that offloading more of the work normally done by your CPU to the graphics card would benefit everyone, Adobe added support for GPU and OpenGL acceleration to the new version of Photoshop.

To make use of the new GPU accelerations, your graphics card must have at least 128 MB of memory and support OpenGL 2.0 along with something called Shader Model 3.0. If you're not sure if you've got all these, you can let Photoshop CS4 tell you. Go to Edit >> Preferences >> Performance and look for the check box for "GPU Settings." If your GPU qualifies, the model will be listed and the box will be checked. If this area is blank, Photoshop doesn't think your system has what it takes. If you think you do have a GPU that is up to the task, make sure your video driver is updated. If that still doesn't do the trick, consult the troubleshooting section in this article on Adobe's website.

With GPU acceleration enabled, the experience of using Photoshop changes dramatically. Now when you zoom in and out, the size of everything changes smoothly and evenly. Better yet, the view remains sharp at all magnification ratios. No more jaggies when viewing at an odd percentage. When you zoom above 500% you can now turn on a pixel grid view that outlines each individual pixel so you can clearly see what you are editing.

If the entire image won't fit on the screen, you can activate the "Bird's Eye View" feature to show you where you are at. Just hold down the "h" key to activate the hand tool, then left mouse click on your image. The view will zoom out to show you the entire image and a bounding box will appear over top of your image centered where you clicked. If you want to scroll elsewhere in the image, just move your mouse around and the box will follow. Let go and the image will zoom back into the same scale you were at but centered at the new location. And all this happens quickly and smoothly. No waiting on screen redraws and no jaggies.

Hold down the space bar and you can "flick" scroll the image with your mouse. Just click and drag in the direction you want to scroll and the image will move smoothly, slowing to a stop after you let go of it. If you're familiar with the interface of the current iPods, you'll know what I mean.

You can also rotate the view to any angle you want smoothly. The image itself isn't rotated, just your display. This lets you work on things however is most comfortable for you. You'll love this feature if you use a graphics tablet but it can help with detail work even if you edit only with a mouse.

After using Photoshop CS4 for a while now, I recently had the occasion to use it on an older computer again that didn't support GPU acceleration. The difference is staggering. Once you get used to the accelerations, there's no going back. If you're already using Photoshop CS4 and your graphics card doesn't support this feature, get a new graphics card. If you haven't yet upgraded to CS4 and work on large files, run, don't walk, to get the upgrade. Not only do the acceleration features save you time and frustration, they are downright fun to use.

Date posted: February 22, 2009


Copyright © 2009 Bob Johnson, Earthbound Light - all rights reserved.
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