The higher the threshold, the more areas are concerned by sparkling (0.0-0.1).

When this value increases, the central spot and rays widen (0.0-1.0).

This is ray length (1-100). When you reduce it, small spikes decrease first.

Number of starting points for spikes (0-16). It's the number of big spikes. There is the same number of small spikes. When number is odd, small spikes are opposite the big ones. When number is even, big spikes are opposite another big spike.

This is angle of first big spike with horizontal (-1 +360). -1 determines this value at random. If a spot has several pixels within required threshold, each of them will generate a sparkle. If angle is positive, they will all be superimposed. With -1, each sparkle will have a random rotation resulting in numerous thin spikes.

This option determines the number of sparkles on your image. It indicates the percentage (0.0-1.0) of all possible sparkles that will be preserved.

When you decrease Opacity (0.0-1.0), sparkles become more transparent and the layer beneath becomes visible. If there is no other layer, sparkle saturation decreases.

This option should change sparkle hue at random... (0.0-1.0)

This option should change sparkle saturation at random... (0.0-1.0)

Gives to all central pixels the luminosity of the brightest pixel, resulting in increasing the whole sparkle luminosity.

Instead of selecting brightest pixels in image, Sparkle will select the darkest ones, resulting in dark sparkles.

Instead of creating sparkles on brightest pixels, this option creates an image border made up of numerous sparkles.

You can change there the color of central pixels. This color will be added in Screen mode (Multiply if Inverse is checked). You can select between Natural color (the color of the pixel in the image), Foreground color and Background color.