AgMax Compositor Tonemapper for Blender
The nodegroup in use in the realtime viewport compositor.
AgMax is a compositor nodegroup for Blender that is an alternative to the built-in Filmic, AgX, and Khronos PBR Neutral tonemapping view transforms. With AgMax, you can control the highlight rolloff curves that the tonemapper uses, which you can’t do with Blender’s built-in view transforms.
AgMax is on its default settings.
AgMax is like the best of both worlds of AgX and Khronos PBR Neutral. AgMax smoothly desaturates highlights to white (avoids the 6-color problem) like AgX and Khronos both do. AgMax allows for highly saturated colors unreachable in AgX (like Khronos) while avoiding Khronos’s shortcomings:
- “Khronos PBR Neutral” does not rotate hue to compensate for the Abney Effect (shown below). (AgX does, but the amount of it isn’t adjustable)
- “Khronos PBR Neutral” has brightness inconsistencies that create artifacts in certain situations (shown below).
AgX, in addition to its desaturation, has other shortcomings that AgMax tackles:
- AgX compensates for the Abney Effect but not very effectively and not without side effects. AgX shifts the hue of pure blue towards cyan even when the blue isn’t bright enough to desaturate towards white. In other words, AgX’s Abney Effect compensation method inadvertently rotates hues when there’s no Abney Effect.
Abney Effect Compensation
The Abney effect describes a perceived hue shift when white is added to saturated colors. It is the most noticeable with pure RGB blue. It also affects red and green. If a tonemapper that desaturates bright colors to white does not account for the Abney Effect, bright reds appear pinkish and bright blues appear purplish.
AgX has fixed Abney Effect compensation. Khronos PBR Neutral doesn’t compensate the Abney Effect. Khronos’s lack of Abney Effect compensation (as well as brightness inconsistencies) can be seen in the pinkish-looking flame and the purpleish-looking ball in Khronos render:
AgX rotates hues to compensate for the Abney Effect, but AgMax does a better job.
Though AgX adjusts for the Abney Effect far better than Khronos does, AgX shifts the blue hue towards cyan even for darker shades where the Abney Effect is not present and thus need no hue rotation.
AgMax’s user-adjustable Abney Effect hue compensation makes fire and sunset scenes look great.
AgMax allows the artist to adjust the amount of Abney Effect hue compensation to their heart’s content:
Artifact-Free
Khronos PBR Neutral suffers from artifacts with some colors because of its brightness inconsistencies:
AgMax, like AgX, is artifact-free.
Adjustable Dynamic Range Compression
Unlike Blender’s built-in view transforms, the AgMax tonemapper’s highlight rolloff curves can be tweaked.
How is adjustable dyanmic range compression useful? A tonemapping algorithm that has a fixed highlight rolloff curve (e.g. Filmic, AgX) squashes highlight brightness regardless of whether your scene actually needs it. A backlit landscape may look great with strong dynamic range compression, and the same amount of dynamic range compression may be too much for an evenly lit portrait shot. Have you ever used the “Standard” setting rather than Filmic or AgX because Filmic and AgX made a scene’s highlights look super dull? Not all scenes look good with a very soft, filmlike highlight rolloff curve. Khronos PBR Neutral partially solves this problem by having more saturated bright colors, but—as explained previously—it (at the time of writing) produces unpleasant artifacts. Its highlight compression isn’t adjustable either. Different scenes need different amounts of highlight rolloff.
Adjustable dynamic range compression makes AgMax versatile. Easily adapt your tonemapping to…
- compress the huge dynamic range of a sunny outdoor scene
- not unnecessarily squash the highlights of an evenly lit indoor scene that has low dynamic range
…by moving 1 slider.
Highlight Desaturation Knee Softness
AgMax’s “Highlight Desaturation Knee Softness” slider controls the softness of the transition between bright saturated colors and desaturated highlights.
Setting the knee softness control closer to 1 makes AgMax start desaturating bright colors before they hit maximum RGB brightness, making a filmic look akin to AgX’s smooth and desaturated highlights. Setting the knee softness control closer to 0 makes AgMax preserve bright colors’ vibrance like Khronos PBR Neutral does.
More Examples
AgMax’s colors are more vibrant than AgX’s. AgMax’s Abney Effect compensation prevents the purplish glow and the pinkish flame looks that Khronos produces. Khronos darkens colors that are dark and desaturated but not colors that are bright or saturated; this inconsistency makes the relative brightnesses of colors in the water’s reflection look off.
Colorimetric Test Imagery
a .blend file containing the AgMax compositor node