From: Alan Friedman <alan@greatarrow.com>

Date: November 28, 2005 12:11:44 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: What a difference a little work makes

On Nov 27, 2005, at 12:44 AM, Steve Bryson wrote:

That sharpening was for a radius of 1 or so, I'm heeding your advice.  Think it needs to be

smaller still?  I tried several sizes before settling on the image you see, but perhaps it 

could be better.

Steve

Hi Steve -

1.0 pixel diameter is good but I probably should add a bit more to qualify my comment. Lunar subjects are fun to process because they generally have lots of tonal range due to the brightness of the image and hence a high S/N ratio. But images captured near the terminator will often have values at the top and bottom of the histogram (full black and white) - and many areas that display dramatic contrast differences. These are easily blown out by a heavy hand with the unsharp mask command.

I like to use a small pixel radius on these images (.8 -1.4 for example) but it can also be helpful to use the selection tools in Photoshop to omit the brightest whites and deepest blacks from the sharpening routines in the first place and constrain the contrast enhancements more to the middle ranges. Using the color range command in the select menu and choosing the highlights of the image is a good way to do this (once you have a good selection for the values you want not to sharpen, select the inverse for sharpening.) 

I think you will find this technique gives powerful control. Selecting the areas for processing will help avoid the artifacts such as the region you noted in your posted image that are inevitable when using global selections.

best,

Alan