Sharpen Filter

Accurate Image Manipulation for Desktops

# Sharpen 7-band (1st, September, 1999)

# Description

> Powerful sharpening filter, effect is controllable over 7 tonal bands. It utilizes the popular unsharp mask over 3x3 kernel (the same as radius 0.5 in Photoshop). The possibility to adjust the sharpening amount over the 7-bands provides far better quality than a simple threshold cut.

# Selection Dropdown

> First tell the filter what kind of image you are editing: Low Key Image, Middle Key Image or High Key Image. These affect slightly to the division of the bands. If the "1/7 tone" slider responds too strongly set selection to Low Key Image if the "1/7 tone" slider responds too slightly set selection to High Key Image.

# Check Boxes

> 0/255 Inv

> > This is a preview function only. When enabled it will give visual feedback for pixels that have channel value 0 or 255. This greatly helps in applying the amount properly. To see the effect slowly enable/disable the 0/255 Inv check-box.

# Sliders

> Amount, 0...500. the initial amount of the sharpening. 500 is approximately equal to Photoshop USM at amount=500, radius=0 and threshold=0.

> n/7 tone, these 7 slider affect to seven perceptually equal ranges, 1/7 tone is the most dark range and 7/7 tone is the brightest range. The value of these sliders is percentage from Amount, ranging from 0 too 400%, with default value 100. Note that setting a slider to 0 completely disables sharpening for that range and setting it to 400 will multiply the sharpening amount by 4 for that range. (The spline that the x/7 tone sliders control is smoothed slightly).

# Notes

> This filter is not very usable in gamma spaces since the two or three lowest sliders (in the black-end of the range) do not notably affect to gamma images. This is not the problem of the filter but is due to the image-gamma. It is possible to write the filter in such way that it 1) removes the gamma compensation, then 2) applies the sharpening and finally 3) re-applies the image-gamma. Since the filter works in 31-bit/color this does not degrade the quality but it makes the filter extremely slow. It is already a little slow because of all the calculation needed.

> Please note that the sliders are strong.

> First thing to do when the filter opens is to Shift-Click the preview + button in order to have the 1:1 zoom in the preview box. Then drag the image so that a representative area is shown, the dragging is not limited to the preview box boundaries.

# Author

> Timo Autiokari. Homepage: Accurate Image Manipulation for Desktops

# Usage and Distribution Rights

> Free to download and use, all re-distribution prohibited.

# Filter Engine

> FilterFormula v 1.1, by ATS/Graphics