Re: [APML] Shaping Stars

[Matt BenDaniel <matt@starmatt.com>]

At 05:30 PM 10/27/2001 -0600, Jon Kolb wrote:
>Perhaps this was discussed in a thread I missed, but what exactly do you do
>to shape the stars?  I'm curious because some of my recent PPF scans are so
>grainy that the stars have ragged edges.  

Jon,

I should write an article about shaping stars. I learned it originally from Sean Walker, but I have refined it. From looking at various other astrophotographers' work, I suspect certain individuals are doing something similar, but they don't talk about it.

The reason to shape stars is that when contrast is increased (by skillful curves), the stars look burned out. They appear larger, less colorful, and have harsh edges. This typically also is seen as clipping on the high end of the histogram. This article addresses clipping: http://people.ne.mediaone.net/mbendaniel1/articles/curves.htm

We spend a lot of time focusing critically, getting accurate guiding, because one hallmark of a quality image is tight round stars. But what if the stars look blobby and massed together? In very star-rich areas, the stars may be so crowded that delicate nebulosity is highly obscured.

To shape stars, I select the stars with magic wand and create a curves layer. It is tricky, especially if some of the stars are embedded in nebulosity. You want to be careful to avoid putting dark rings around the stars or changing their color.

If the stars are shaped well, in each star you see a very bright level in the center, then it rolls off gently. The halo color is emphasized. The star appears softer, rounder, more 3D. And star shaping can actually "split" close stars by making them smaller.
--
Matt BenDaniel
http://starmatt.com


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