5D.Flare

INPUT CLIPS
LightMap: a clip containing bright light sources to create flares.
Background: the background on which the flares are drawn.

Tips:

• The light map clip controls where the flares will be drawn. Potentially EVERY PIXEL can have a flare applied to it. If this is the case it can take some time to process... By default only the brightest pixels are selected with intensity values between 250 - 255. You can alter these values to suit using the parameters Low Light and High Light.
• You can also display the Lightmap (as created with the bounding box and threshold values) rather than processing the full final effect; this helps you check out exactly which points will be flared. Switch Light Map Only on (this is default anyway).
• Not all of the input clip has to be used. Use the Bounding Rectangle overlay to describe a rectangle within the image. Only pixels within the Bounding region will be considered for a flare.
• Always check out the effect at full resolution as more pixels may be picked and the ffect intensified.

Halo Fringes (Min: 0 Max: 1000 Default: 100)
This controls the number of radial lines eating in to the central halo. It is combined with random weightings to give the final effect. In the eye, the central brightest part of a light source image often looks as if it has been 'eaten into' by radial lines, so it's no longer symmetrical and smooth (even when the original light source is). This is due mainly to inconsistencies in the material of the eye. It doesn't happen with artificial lenses.

Halo Strength (Min: 10.0 Max: 1000.0 Default: 100.0)
Adjusts the relative importance of the halo effect.

Halo Fr(i)n(ge) Str(ength) (Min: 0.0 Max: 100.0 Default: 50.0)
Controls how much (on average) each radial line halo fringe, eats in to the central halo.

STREAKS
Number (Min: 0.0 Max: 1000.0 Default: 10.0)
Specifies the number of streaks to use. These are centred on the light source and are somewhat random in orientation and length (but consistent from frame to frame throughout a sequence!).

Length (Min: 0 Max: 200 Default: 10)
Sets the maximum streak length. Streaks are generated from half this length to this length.

Rotate (Min: 0.0 Max: 360.0 Default: 0.0)
Animating this will give some of the effects seen in streaks when the observer moves.

Strength (Min: 10.0 Max: 1000.0 Default: 100.0)
Adjusts the relative importance of the streak effect.

Mono chromatic (Min: 0.0 Max: 100.00 Default: 5.0)
Increases or reduces the color content of the streaks.

GLOW
Radius (Min: 0.0 Max: 50.0 Default 1.0)
Controls the radius of the glow effect around each pixel in the light map. These separate glow effects add up to form the overall glow around an extended light source.

Glow (Min: 10.0 Max: 1000.0 Default: 100.0)
Adjusts the relative importance of the glow effect.

REFLECTIONS
Number (Min: 0 Max: 10 Default: 0)
Controls how many times a light source is reflected. In reality, this depends on the number of surfaces (e.g. lens elements) there are in the path of the light.

Strength (Min: 0.0 Max: 100.0 Default: 5.0)
How much of the light source intensity is reflected at each reflecting surface.

Scale (Min: 1.0 Max: 100.0 Default: 10.0)
How reflected positions of lights are scaled about the center of the image. The reflecting surfaces are treated as a set of evenly spaces parallel plates. Animating this control can add a bit more interest.

RENDER
Contrast (Min: 0.5 Max: 3.0 Default: 1.35)
Controls the overall contrast of the combined flare effects before they are composited over the background image. Can usually be left at the default, or perhaps lowered to make the effect more subtle.

Light Map (Default: On)
On=1: When starting to use this effect Light Map Only is always On. This displays pixels within the bounding box and within the Low and High range you can see very quickly which pixels will be used for the flare generation.
Off=0: Turn Off when you have found the pixels you want for the full flare effect. Be prepared for a long wait if your chosen area is densely packed!

ROI INTENSITY RANGE
Low Threshold (Min: 0.0 Max: 100.0 Default: 90.0)
High Threshold (Min: 0.0 Max: 100.0 Default: 100.0)
Use to bound the intensity levels to consider when creating the flares.

ROI BOX
Min XY (Default: bottom left)
Max XY (Default: top right)
Delimits the bounding box. Only pixels within the box will be considered for flares.

ROI POINT LIGHT SOURCE
This is a new feature for v3.0. Instead of the bounding box determining the area, a point on the image can be chosen instead.

Point XY (Default: image center)
The location on the image where a flare is drawn, if the DoPoint option is on.

Point Boost (Default: 1)
The default value will give a flare based on 1 pixel, a small and dainty flare. Increase to boost the effect; 2 gives a flare based on a 2x2 region, 3, a 3x3 region......

DoPoint (Default: Off)
Off=0: the bounding box region will be used for creating flares.
On=1: the point XY location will be where the flare is drawn.

PRINCIPLE OF OPERATION
Choice of the light map is important. If most of the image falls within the intensity threshold range then it will take a LONG time to calculate all the flares. Flare contains a simple threshold and bounding box which can be used to selectively 'thin down' the input image to create a suitable light map.

Both diffraction halos and diffraction streaks are calculated using the physics of diffraction. This must be done carefully, with spectral sampling at lots of wavelengths before conversion back to red, green and blue. In spite of this, it is quite fast. The 'cheat' is that angles are greatly exaggerated - each image pixel is treated as if it covers only one thousandth of a degree! The main cost in execution time is a large glow radius. The glow kernel is not symmetrical and attempts to use separable symmetrical kernels and fiddle with random numbers when the kernel is used, haven't given satisfactory results, so far.

Some of the effects that Flare can create are quite subtle, and to be convincing, it should be applied carefully. Lights treated by Flare do look much more like real lights do in real scenes than the anaemic 'maximum brightness pixels' that traditionally was the best 3D renderers could do to represent very bright objects. There are four main effects, which Flare can add to a light map. These are modelled (loosely) on (exaggerated) physical phenomena that do actually give rise to the appearance of real lights.

• Scattering of light in a volume surrounding a light source by moisture, dust, and sundry junk. We assume this is the same for all light colors and is somewhat random (e.g. mist isn't perfectly uniform). We treat this with a filter kernel that distributes light from light map pixels somewhat unevenly into the output image. We call this a glow. The glow radius should depend on distance of the light from the observer, but this is impractical, and it's pretty convincing without this. If the light map comes from a 3D renderer and the bright pixels of a light source surface get fewer and/or dimmer depending on distance (as they will), the size of the glow will vary with distance more or less correctly.
• Diffraction by the lens aperture (or eye pupil). This effect in reality spreads out light from a 'point' to cover a disk on film or at the back of the eye. In fact, every point gets turned into an endless set of circular light and dark bands, which die off rapidly in intensity moving out from the middle. Also, the spacing between the light and dark bands is different for different colors, so white 'points' get spread out in to rainbow rings.
  In the real world, this effect (while very real indeed) is pretty marginal in size - the central bright band for red light from a point subtends an angle of about 0.04 degrees! However, exaggerating the size of this effect, seems to model well things like the yellowing of car headlamps around the edge of the beam and stuff like that. It's really useful, and we call this the halo. It's also good for simulating an effect due to fibres near the edge of the lens in the eye, which can cause faint rainbow color rings some distance from bright lights in dark surroundings.
• Streaks also modelled by diffraction. Streaks of light from bright light sources are a cliché. They are also always visible in reality and are very important indicators of the brightness of a light source. They also often contain rainbow colors. These can come from filters deliberately put in front of the lens (the grossest!), eyelashes acting as a very poor diffraction grating and fibres in the edges of the crystalline lens of the eye (see above). Streaks are somewhat random in number (except where a diffraction filter is being used), and rotate as the observer moves. Some can become 'stronger' while others become 'weaker' too, as the viewer moves, while all remain visible to some extent. Rainbow streak like things can also be seen as a result of refraction (e.g. in dirty windscreens - although that might be partly diffraction from parallel smears in grease from windscreen wipers, as well). Again, these effects can be really useful.
• Reflection of light sources in lens elements. We have a very simple model of this at present.

 

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