Glare

Bright lighting in CG images is often difficult to accomplish. Many times bright areas appear as solid white splotches with unrealisticly hard edges. Glare comes to the rescue in these situations by giving a halo around extra bright areas.

In particular, Glare is extremely helpful when an image has areas of "over-exposure." Over-exposure occurs when color values move beyond the solid white value of 1. While the color white (R:1.0, G:1.0, B:1.0) may look the same as the color extra-bright-white (R:2.0, G:2.0, B:2.0), Glare treats them differently, giving larger halos to brighter objects.

It should be noted that Glare gives realistic glares and flares from any bright source - not just lights. For example, it will create glares off of shiny metals, flares from reflections on a water surface or glass object, etc.


Procedure

Create a scene containing bright objects.

In the render dialogue box, select mental ray as the rendering type.

Click on Options, and in the options dialogue box select Glare as the output shader.

Edit Glare's parameters.


Parameters

Glare can begin to slow down rendering times when the scene has large bright areas. Quality lets the artist set the tradeoff between detail and speed. Lower Quality settings will cause Glare to run more quickly, but may cause the glare halo to be "boxy," whereas Higher Quality will give a better overall effect, but will of course take longer. Generally, a mid-level setting is appropriate for most scenes.

Spread controls how sensitive Glare is to bright objects. Lower values for Spread will cause smaller glare halos while higher values will cause larger glare halos. Very high values will cause dark objects to have halos. (Try not to abuse the Spread parameter. The best way to increase an object's halo is to increase its brightness, not to increase the Spread.)

Overlay Only mode will cause Glare to produce a glare "overlay". The overlay is an image of the glare effect only; the original underlying image is removed. This mode is useful when render speed is critical, so that Glare can be run on a lower resolution image to produce an overlay, which can then be composited with a higher resolution underlying image.

Verbose Mode turns on verbose output, so that the progress of Glare can be monitored.

Streaks

When active, the Streaks feature allows you to specify a .pic file that will be used to create a `streaking' effect, as seen when looking at bright images through glass or, in photographs, through a camera lens.

Image is the streak template that Glare uses to draw streaks. Two example images are provided: "Glare-Eye" models the streaks caused by the human eye, and "Glare-Star" models the streaks cause by a star-filter camera lens.

Scale controls how big the streaks image should be. A value of 1 means that one pixel in the streaks image should cover one pixel in the output image. Smaller values will make the streaks image smaller, larger values make the streaks image larger.

Contrast controls the variation in brightness between the streaks and the darker region between the streaks. A value of 0 causes the streaks and dark regions to have the same brightness; a value of 1 causes the streaks to have the maximum brightness and the dark regions to be black.

Region

Region sets where the glare takes effect. The two choices are Entire Image, causing all of the image to be glared, or Specific Objects, whereby you can select which objects will receive the glare effect.