Russell Croman Astrophotography  

 

 

GradientXTerminator

Plug-in for Adobe Photoshop for Windows® and Macintosh®

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GradientXTerminator is a gradient removal plug-in for the Windows version of Adobe Photoshop that is fast, easy to use, and really works. It can process 16-bit or 8-bit images, grayscale or RGB color. It easily tackles large-scale gradients from light pollution, but can also handle vignetting and even tricky edge, corner, and circular gradients that are very hard to deal with otherwise. And assuming you already use Photoshop in your work flow, you may now have one less program to transfer your image into.

Gradients, whether caused by light pollution or image calibration errors, have always been a problem with amateur astronomical imaging. In the past, image processing programs have tried to correct gradients by automatically determining how they affected an image. This was usually detrimental, since the software could not easily differentiate between background areas and actual objects. A bright galaxy in the center of an image, for example, would "fool" the software, resulting in a dark halo around the galaxy.

More recently, tools have become available that allow the user to tell the software what parts of the image are background by placing small markers on the image. This was a great leap forward and produced much improved results. But for complex gradients that arise from multiple stray light sources and flat-field calibration errors, these tools are less than convenient. They can sometimes be made to work, but tens or even hundreds of background points must be marked for the tool to build an adequate mathematical model of the gradients.

Enter GradientXTerminator. Three key features make this a superior tool:

  1. Simple, intuitive user interface.
    Image processing tools sometimes seem like they were written by computer programmers for computer programmers. Obscure numerical parameters, excessive numbers of settings, and clunky user interfaces are a barrier between you and the results you want. With GradientXTerminator, you don't have to be a mathematician to make it work.
  2. Familiar background selection methods.
    You probably already use Adobe Photoshop to do the final processing steps on your images. You are probably already familiar with its rich set of selection tools, such as the Lasso, Magic Wand, and Color Range tools. Rather than forcing you to click many times to place background markers, GradientXTerminator allows you to use the tools you already know to tell it where the background is.
  3. Sophisticated mathematics.
    Behind the friendly and comprehensible user interface is an advanced mathematical modeling engine. The hardest part of correcting a gradient, even when a tool is told where the background is, is what to do in the rest of the image. GradientXTerminator finds the optimal model of the gradient based on the input you give it.