Image Processing Tips
Removing Diagonal Bands
I find that my Logitech QC 4000 and SAC7A cameras both tend to produce diagonal bands. In this tutorial I will show the reader how to safely remove the bands without sacrificing image detail. The first step in the process is to do the normal alignment and stacking with Registax. Instead of applying wavelets you will want to save the image as a 16 bit TIFF image after the stacking process. Do not apply any wavelets at this point. Next, open the image with Astra Image 2.5MAX and split the image into its RGB components.
After splitting the image into its RGB components the next step is to edit each color plane with the Fast Fourier Transform (FFT) editor. The FFT of each color plane will contain the bulk of the image detail in the central portion of the two dimensional graph. The image noise )banding) will be found in smaller regions outside the central portion of the image. The FFT editor allows us to edit out those outlying features (noise). You will want to experiment with the editor to see what happens when you edit different parts of the FFT.
Once the noise has been edited out of the FFT click the OK button. Astra Image will now do an inverse transformation giving you a relatively noise free image. Repeat this process for the green and red color planes.
After each of the color planes has been edited with the FFT editor and the inverse transformations have been applied it is time to recombine the edited versions of the color planes back into a color image. Select the RGB Combine option under the Process menu. In the RGB Combine dialog select each of the edited color planes and recombine them.
Now you are ready to save the image as another TIFF image that you will open with Registax for wavelet processing.
After wavelet processing you can adjust the color balance and do any other post processing that you would normally do. What started out as a hopeless looking image has turned out to be a fairly nice image.