Removing stripes from images

Problem description

Film scanners are not perfect. Sometimes, tiny stripes can appear in the final image. The stripes are so tiny that they are not visible under normal circumstances. However, they are noticeable at some particular magnifications (like 66%) in Photoshop. The stripes are just one pixel wide and create a pattern of even/odd lines. The average difference between even/odd pixels is just 1 / 256. This look like unimportant difference but due to aliasing with printer resolution, the stripes may create significant banding of the final print. Especially at areas without any rapid change of color (like blurred background). See example:

original image

scanned print

The two images above demonstrate the banding effect when such problematic image is printed. Notice the vertical stripes in the right image. Left image was created by HP PhotoSmart S20 film scanner. The right image is scan of the left image printed on HP photo printer.

crop at 100% zoom

crop at 66% zoom

Above is a crop of the original image at 100% zoom (actual pixels) and at 66% zoom. As you can see, it is impossible to find any stripes in the left image by naked eye. Once the image is zoomed to 66%, the vertical stripes are clearly visible. Below, you can se the same image after it was processed by my program.

result at 100%

result at 66%

The program

Stripes.exe is a free console-based Win32 program for removing tiny stripes from images. The program reads the input file, compute the average difference between even/odd lines for different color regions. These values are used in second phase to minimize the "striping" effect.

Only 8 bits per channel uncompressed TGA files are supported. Use Photoshop/ACDSee or any other tool to convert your images to/from TGA format.

Download

Stripes version 1.06, 6-May-2003