Pascal Gilcher split RTGI into separate Diffuse and Specular shaders in September 2025, making the effect faster, more stable, and easier to maintain. The change turned one familiar effect into two lighting tools with different controls and different visual failure modes.
The split matters most when you tune a preset. RTGI Diffuse handles indirect lighting and ambient occlusion, while RTGI Specular adds glossy reflections according to surface roughness. Treating both as interchangeable versions of the same shader usually leads to muddy lighting, plastic-looking surfaces, or settings that seem to fight each other.
The June 2025 RTGI sampling overhaul arrived before this separation, when reflections and indirect lighting were still discussed under the broader RTGI umbrella. The later architecture makes more sense once you stop thinking of RTGI as one switch that simply makes a scene look more ray-traced.
Its main controls reflect those jobs. Bounce Lighting Intensity sets the strength of indirect light, while Ambient Occlusion Intensity changes the shadowing between nearby surfaces. Object Thickness matters because ReShade only sees camera-facing depth, forcing RTGI to estimate how far objects continue behind the visible surface.
Color handling also changed with the split. Gilcher added physically based spectral emulation to Diffuse to reduce oversaturation and strange hue shifts that can appear when colored light keeps bouncing through an RGB workflow. The broader problem is well established in spectral primary decomposition for sRGB reflectance, where spectral representations preserve light behavior that three-channel RGB cannot fully reproduce.
You still have to tune the effect by eye. Propagated light should not become brighter than the source feeding it, and excessive AO can crush corners into dirty gray patches. Current RTGI documentation also warns that bad depth alignment from DLSS, FSR, or TAAU can create artifacts that no amount of intensity tweaking will fix.
A low roughness value can make polished floors, wet roads, lacquered furniture, and similar surfaces read more convincingly. Push it too low across an entire game and everything starts looking coated in clear plastic. Higher roughness spreads the reflection until it feels more like broad gloss than a recognizable mirror image.
Gilcher also changed the filtering behind Specular. The separated shader uses anisotropic path-space filtering, intended to produce cleaner reflections with better stability. Quality settings then adjust rays per pixel, with higher modes reducing noise and flicker at a larger performance cost.
Texture normals become especially important here because reflection direction reacts strongly to surface orientation. Launchpad can derive textured and smoothed normals from information available to ReShade, giving Specular more useful surface detail than a raw generic depth buffer provides. Without sensible normals, broad areas can look unnaturally smooth even when the game texture suggests rough material.
The separation also exposes outdated presets. Older configurations can still reference the former combined RTGI shader filename, so ReShade may report missing effects after a user installs a newer release. Updating the preset to the current Diffuse and Specular files is more sensible than hunting for an obsolete shader just to satisfy an old configuration.
Launchpad remains mandatory at the top of the load order for both shaders. Its depth-derived normals, optical flow, and supporting data feed temporal and spatial work inside RTGI. Current versions can also limit Launchpad processing to the data active shaders request, reducing wasted overhead when parts of the lighting stack are disabled.
You can disable one half without making the other conceptually wrong. Keeping Diffuse alone preserves bounced lighting and AO without the glossy reflection layer, while Specular alone can add reflective response without RTGI’s diffuse bounce contribution. The cleaner choice depends on what the game already renders well and which missing lighting cue you are actually trying to replace.
The split matters most when you tune a preset. RTGI Diffuse handles indirect lighting and ambient occlusion, while RTGI Specular adds glossy reflections according to surface roughness. Treating both as interchangeable versions of the same shader usually leads to muddy lighting, plastic-looking surfaces, or settings that seem to fight each other.
The June 2025 RTGI sampling overhaul arrived before this separation, when reflections and indirect lighting were still discussed under the broader RTGI umbrella. The later architecture makes more sense once you stop thinking of RTGI as one switch that simply makes a scene look more ray-traced.
Diffuse owns bounced light and ambient occlusion
RTGI Diffuse is the part that changes how light seems to spread through a scene. It estimates bounced illumination from visible surfaces and adds ambient occlusion where nearby geometry blocks surrounding light. A red wall beside a pale floor can therefore push colored light into the floor, while a tight corner can gain darker contact shading.Its main controls reflect those jobs. Bounce Lighting Intensity sets the strength of indirect light, while Ambient Occlusion Intensity changes the shadowing between nearby surfaces. Object Thickness matters because ReShade only sees camera-facing depth, forcing RTGI to estimate how far objects continue behind the visible surface.
Color handling also changed with the split. Gilcher added physically based spectral emulation to Diffuse to reduce oversaturation and strange hue shifts that can appear when colored light keeps bouncing through an RGB workflow. The broader problem is well established in spectral primary decomposition for sRGB reflectance, where spectral representations preserve light behavior that three-channel RGB cannot fully reproduce.
You still have to tune the effect by eye. Propagated light should not become brighter than the source feeding it, and excessive AO can crush corners into dirty gray patches. Current RTGI documentation also warns that bad depth alignment from DLSS, FSR, or TAAU can create artifacts that no amount of intensity tweaking will fix.
Specular owns roughness and glossy reflections
RTGI Specular focuses on the reflective part of indirect lighting. Surface Roughness decides whether reflections appear sharp and mirror-like or spread into a softer sheen, while Fresnel F0 controls how strongly surfaces reflect light when viewed head-on. The current default F0 value is 0.04, which is appropriate for many common non-metal materials.A low roughness value can make polished floors, wet roads, lacquered furniture, and similar surfaces read more convincingly. Push it too low across an entire game and everything starts looking coated in clear plastic. Higher roughness spreads the reflection until it feels more like broad gloss than a recognizable mirror image.
Gilcher also changed the filtering behind Specular. The separated shader uses anisotropic path-space filtering, intended to produce cleaner reflections with better stability. Quality settings then adjust rays per pixel, with higher modes reducing noise and flicker at a larger performance cost.
Texture normals become especially important here because reflection direction reacts strongly to surface orientation. Launchpad can derive textured and smoothed normals from information available to ReShade, giving Specular more useful surface detail than a raw generic depth buffer provides. Without sensible normals, broad areas can look unnaturally smooth even when the game texture suggests rough material.
Running both makes the split useful
Diffuse and Specular are designed to run together, but separating them gives you control over which lighting problem deserves the GPU budget. A scene with flat lighting may benefit heavily from Diffuse, while a game already doing decent ambient shading might gain more from restrained Specular reflections.The separation also exposes outdated presets. Older configurations can still reference the former combined RTGI shader filename, so ReShade may report missing effects after a user installs a newer release. Updating the preset to the current Diffuse and Specular files is more sensible than hunting for an obsolete shader just to satisfy an old configuration.
Launchpad remains mandatory at the top of the load order for both shaders. Its depth-derived normals, optical flow, and supporting data feed temporal and spatial work inside RTGI. Current versions can also limit Launchpad processing to the data active shaders request, reducing wasted overhead when parts of the lighting stack are disabled.
You can disable one half without making the other conceptually wrong. Keeping Diffuse alone preserves bounced lighting and AO without the glossy reflection layer, while Specular alone can add reflective response without RTGI’s diffuse bounce contribution. The cleaner choice depends on what the game already renders well and which missing lighting cue you are actually trying to replace.
