25th September 2003, 03:30 PM
What is the Unsharp Mask?
Dear Togu and other Gurus of PS:
I am always puzzled by the Unsharp Mask function, known affectionately as USM, not related the other USM of Canon fame.
What exactly is the "Unsharp" mask and why do people use it to "Sharpen" their photos? Strange for people like me. Why would I choose the "Unsharp" function to perform a sharpening fuction? What does it actually do, algorithmically or optically?
I notice that their are 3 sliders when I pull up the USM function. The first one, Amount, is quite obvious. When I slide back and forth I can see the preview effect immediately.
It is the other two sliders that really made me scratch my head until I botak. What is the meaning of Radius and Threshold? I move the sliders for these two back and forth, I can see some changes to the picture, subtle changes, which seem a bit like contrast settings sometimes and brightness settings at other times. What exactly is happening when I adjust the radius and threshold?
What do I look for to determine the correct settings of all these sliders?
Thanks to all for any comments, instructions, and teaching.
Your humble PS Goondu.
25th September 2003, 03:34 PM
26th September 2003, 05:20 PM