Focus Blur Plug-in

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# Throw a shadow with Focus blur

Amending about mis-translation will be welcomed. I'm waiting at e-mail and board.

- Prepare an object
- Prepare a shadow
- Make depth map
- Blur
- Finish
- Explanation

## Prepare an object

Prepare an object in transparent layer. Let set a cylinder at this time. Select the figure of object with rectangle and ellipse. Fill width with a gradient black to white with blend tool. And adjust light and darkness of object with curve tool.

## Prepare a shadow

Make a shadow just match for object. I chose simple way. How to make black image with same figure. Duplicate layer. Lock alpha channel. And Fill with FG color (if you don't understand, Drag and Drop Black). Shear the layer, and shorten with re-size layer. You can change a layer boundary size at this point, but you should keep a space for blurring radius. The last of this part, Move the layer, adjust bottom of shadow and object. If shadow has been out from bottom of object, Erase it.

## Make depth map

Amount of this map will be distance of object to shadow. Create a new layer at the same size as shadow layer, because offset doesn't able to specified. Duplicate layer is better than to create, because it has same layer offset. Fill with a vertical gradient with blend tool at bottom of cylinder to far (over the end of shadow by horizontal line). You can crop width of the layer, because it has only vertical gradient. (I've met a bug in blend tool, so I've done at this time)

## Blur

Check alpha channel is unlocked in blurred layer. Apply Focus blur with depth map. You can set focal point of depth with preview. Click middle button in preview area. And make it like a shadow. The shadow will be more blurred by far distance. After that, adjust a opacity of the layer, make image natural as shadow (environment light). This work would be done with other layers are visible.

## Finish

It is finished.

This is an example of colored picture. Smooth shadow looks like an air brush art.

## Explanation

This plug-in has been written primarily for creating real shadow it is impossible for Gaussian blur. Many Wilbers would propose to use a layer mask. See below samples.

a | b | c | d | e

- Fig.(a) is two values at left and right.
- Fig.(b) is Fig.(a) blurred smoothly with Gaussian blur.
- Fig.(c) is Fig.(b) added a layer mask takes a vertical gradient, and merged with Fig.(a) as background.
- Fig.(d) is Fig.(a) applied Focus blur with a depth map takes a vertical gradient.
- Fig.(e) is Fig.(a) added selection to vertical gradient, and repeated blur (not Gaussian) at times of pixels for radius.

Fig.(c) is an example of the layer mask, but I feel layer, it looks like glass with dew. Fig.(d) is required blur to make feeling a distance.

Layer mask is function for editing opacity. It is same as selection for filters when marge with original image except that it has edit-ability and interactivity. Two pixels in two layers in same coordinates will be blended with variability. The case of using layer mask with Gaussian blur shows an effect that an value of layer mask makes amount of edge. It can't wrok as amount of blur, because radius and alpha have different measures to preserve color.

While Focus blur decides blurred radius variably. That is blurred coordinates will be changed. It is impossible for layer mask and selection to express this effect.

A technique of repeating blur with selection used in Fig.(e) has resemblance to an effect changes coordinates, because it propagates an effect to neighborhood at every applying. And it can process selection as amount of effect, because it effects in one pixel. But it cause split effect at middle point of selection, some remainder might be made in GIMP.

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