Tämä suodin leventää ja parantaa aktiivisen tason tai valinnan tummia alueita.

For every image pixel, it brings the pixel Value (luminosity) into line with the lowest Value (the darkest) of the 8 neighboring pixels (3×3 matrix). So, a dark pixel is added around dark areas. An isolated pixel on a brighter background will be changed to a big ”pixel”, composed of 9 pixels, and that will create some noise in the image.

In this image, the studied pixel has a red border and the studied 3×3 matrix has a green border. Thus when the pixel marked with ”I” is inside the green border, the studied pixel turns to black.

A larger dark area will expand by one pixel in all directions:

Suodin lisättiin 3 kertaa.

On more complex images, dark areas are widened and enhanced the same, and somewhat pixelated. Here, the filter was applied 3 times:

Tietenkin, jos tausta on tummempi kuin etuala, niin se peittää koko kuvan.

This filter is found in the main menu under Filters → Generic → Erode.