Imager Lens Effects (Bloom) - Arnold User Guide

Bloom or glow is a post-processing effect that will blur pixels above a given threshold across the frame to simulate light bleeding on an imperfect lens.

Input

Input points to the previous imager operation in the chain (so that you can stack them and apply multiple operations serially).

Enable

Enables this imager.

Layer Selection

Selects layers processed by this imager with a glob or operator expression. An imager can use a selection to determine which AOVs will be selected to be processed by the imager at render time. The selection is an expression that can consist of multiple selections concatenated by:

or (union)
and (intersection)
not (negation)
and not (exclusion)
() for nested scoping

Each selection uses glob patterns and regular expressions, and a node will be processed by the imager if the expression matches the node name. By default, glob matching is used unless the selection is in a regex quote, i.e., r'<my_regex>'. For example:

specular or diffuse not r'sss_(direct|indirect)' r'color_(mask1|mask2)' or r'mask[34]'

Bloom Strength

Multiplier or weight of the glow accumulated on the original image. A value of 0 will return the original image.



0 (default)	1	10

Bloom Radius

Spread of the glow across the image: a value of 1 will cause the glow to spread over only a few pixels, while a value of 10 will cover a substantial portion of the image.

Note:

This parameter is only available with the simple mode.



1	4 (default)	10

Note:

bloom_radius is clamped to 1. To disable the effect, you should set bloom_strength to 0.

Bloom Threshold

Controls the minimum value at which pixels glow.



0.9 (default)	2	3

_{Default (0.9) applies bloom to hand and bulb. Higher threshold values show bloom on just the brightest specular highlight of the bulb.}

Note:

The bulb filament cannot bloom because it is behind the glass. Bloom does not take glass (or any kind of light path) into account, only the intensity in the image.

Bloom Tint

Color of the glow for pixels above the threshold.



white (default)	orange

Shape

Shape Mode

The method used to generate the bloom effect. There are three bloom modes:

Simple (deprecated): creates a basic, circular bloom.

Shape File: uses an image file.

Aperture: produces complex effects determined by the camera aperture design.



Simple (default)	Shape File (32-bit lens flare image)	Aperture

Filename

Kernel used to determine the shape of the bloom effect. For realistic results, make sure to center the kernel and make the center pixels much brighter than the rest of the kernel. This will result in bloom only occurring on the bright parts of the image. To capture the large range of intensity between the center of the kernel and the far-away parts, a floating-point image format, such as EXR, should be used.

An example kernel can be downloaded here.