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 Selections and Tolerance Back to the Beta's main page

One of the places in the program where Tolerance comes up is in tools like Magic Wand, Flood Fill and Color Replacer, as well as the Background Eraser. The first three of these all use a single pixel, and therefore a single unique color, as the reference relative to which the Tolerance is computed. This is significant in relation to what happens elsewhere. The Background Eraser has a complex definition of Tolerance that I can't go into, except to say it is entirely different from a Magic Wand tolerance.

Superficially, you might think that a filter like Select Similar would work exactly like the Magic Wand. However, it can't. As a selection modifier, Select Similar has to work on any selection created in any fashion with any combination of selection tools used both in "add to" or "subtract from" selection mode (or, for that matter, with a selection loaded from disk, etc.). That selection can contain many different colors. Select Similar therefore has to do two things. First it has to define some description of "the color of the selection". Second, it has to apply a Tolerance relative to this description. In PSP 7 this Tolerance was fixed inside the code to a value that worked well. In PSP 8 you can adjust this Tolerance to better meet your needs. Note, however, that this is not the same as applying a Tolerance to a unique color as in the case of the Magic Wand. We can probably fiddle with the displayed value of the Tolerance in Select Similar to make it seems more like the Tolerance in the Magic Wand but there is no way to make the two identical in all respects.

Select Color Range is another selection modifier with a Tolerance setting. Like the Magic Wand it uses a unique color relative to which the Tolerance is computed. Unfortunately, however, the metric for color difference is not the same as in the Magic Wand. In other words, the concept of a color difference in this filter is not the same as in the Magic Wand. There are several reasons for this, the main ones being to get a perceptually useful result along with a working Sharpness control. The end result is that the Tolerance in this filter is not directly comparable to the Tolerance in either Select Similar or in the Magic Wand. Again, it is possible to tweak the displayed values of the Tolerance to make them seem more similar to the Tolerance values elsewhere in the program but they will never be exactly identical in all respects. (In fact, the Tolerance range in this filter also needs to be increased a little so that, with white as the reference, black can be selected (or the converse) but that is another matter.)

A couple of tips about working with the Magic Wand.

1. Has anyone noticed that Magic Wand selections can now be antialiased? In PSP7 they could only be feathered.

2. Ever been annoyed that when you select a face with the Magic Wand you get holes in the selection for the eyes, eyebrows, nostrils and mouth? No problem:

Selections > Modify > Remove Specks and Holes. Set Holes and the size of hole to remove. All holes up to that size are filled in. Specks are those isolated blobs of selected stuff outside your main selection. You can get rid of those too.









Balls and Bubbles diffraction map

Can someone help me understand how colors are used in the balls and bubbles diffraction map. What I mean is how are the colors derived? Are they multiplied by the light color, but the base color, are they random? Help me help me I just can't think anymore. I would like to be able to make a calculation rather than wait for the hourglass with each small slide?

The diffraction map colors are completely independent of any other colors you are using in the filter. Depending on how transparent you make the environment map you will see either the fringe colors (fully opaque) or a combination of the fringe colors with the underlying color and/or pattern of the bubble (partly transparent map).

This works just like placing a partly transparent layer over an opaque layer in PSP. However, the combination of ball color and diffraction map color can additionally be modified by the color of the light(s) you are using. Using white or grey light for the illumination will not affect these color combinations but colored lights will.

The diffraction map fringe colors are chosen to to be similar to those you see in thin films (like the skin of a soap bubble). Such colors are cause by interference between light bouncing off the outside and inside surfaces of the skin. Because the skin is very thin (comparable to the wavelength of light) the result is characteristic colors dependent on the thickness of the bubble skin. In this version of the filter we do not vary the thickness of the skin and therefore of the fringe colors. However, the fringe pattern can be changed with a random number generator controlled by the Type control. For a given arrangement of fringes the spacing between fringes (i.e. the scale of the fringe pattern) can be varied with the Fringe Spacing control. As you increase the Fringe Spacing it is as if you are zooming in on the pattern, so that some of it now lies outside the bubble and is not seen. This effect creates fewer and larger fringes, which may make the fringe color appear to change. If you alter the Fringe Control step by step (e.g. in steps of 5 or 10) you can easily see how the large fringe spacing is related to the small.

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