Saturday, 23 February 2008

Lightzone: getting the most out of regions

Silbury Hill and Avebury, Wiltshire, January 2007

This is another in my series of tips on using Lightzone. Regions are applied somewhat differently in Lightzone than other applications. Personally I find them easier to work with than masking in Photoshop (for example) and the ability to change at will at any time is a big advantage.

Here are a few things I've picked up along the way about using regions effectively. For all of the illustrations here I've split the area in the region to be a before/after shot - the editing tools don't provide the clean slice through the middle.

ND graduated effects

Placing zones outside the image area

As I shoot quite a lot of landscapes with horizons, a ND filter is an invaluable tool. Unfortunately, I've not always got one handy. There are also times where a straight edge filter isn't going to help. A polygon region can be used for this, together with a large feather area to soften the transition. To get a similar effect to a ND filter, we want the feather to apply edge to edge. This is where placement of the region outside of the image area is needed. To do this, zoom to smaller than the edit window size (typically 1:4 or smaller). As the feather is rather loose, we don't need to be too worried about precise zone placement.

Running regions outside of the image area is an important feature as it is the way to apply selective feathering.

Feathering and edge placement

Polygon region with small feather

When working on isolating a specific feature or object, we want an adjustment that provides a natural look without harsh transitions. I find that applying the feather to overlap the edge of the isolated feature helps with this. In the case above, I've only needed a small feather region as the effect on the surrounding part is rather limited.

Below I've done something similar but with a much large feather area for a smoother blend.

Region types

Bezier region with large feather

Although there are 3 region types (polygon, spline & Bezier) I almost never use the spline. I find the other 2 give me all the control I need. Polygon for straight edged features, Bezier for the rest. If picking out an edge with a Bezier region, it is best to place a point at every high & low spot along the curve to get a smooth match. Sharp corners can be produced with 2 points close to one another.

Editing large areas

If you are editing a very large area then a handy trick is to pick out a small portion for testing the changes. this minimises the amount of re-drawing the Lightzone does. Once happy, disable the tool (deselect the "tick" mark), place the area more accurately then re-enable the tool.

This is particularly useful when working with large files such as stitched panoramas or MF & LF scans.

Inverse versus normal

Sometimes we want to apply changes to a large area excluding a small portion. In this case it is best to place a region around the small area and use the inverse button on the tool it applies to.

If you wish to apply one set of corrections to one area and others to the rest, select the initial region and then copy it. There are 2 ways to copy: linked (--C on Windows) and unlinked (-C). Linked means that region changes in any of the linked tools apply to all the other tools in the link. Unfortunately, Lightzone doesn't let you know which are linked. I suggest using some sort of naming convention for the tool names to indicate the linked tools.

Black and white conversions

One of the great things about being able to apply regions to pretty much all the tools is that you can apply selective black and white filters. When a region is used for black and white conversion, that area is fixed and further B&W tools don't affect the region. Thus, if you wish to apply a yellow filter to the sky and red elsewhere: mark the region around the sky & apply the yellow filter, then apply a red filter with no region. The second filter ensures all parts of the image convert to monochrome without affecting the previous filter.

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