Work in layers (read this first)
Atmos Forge works like a photo editor with layers — with one important difference: every action is flattened the moment you apply it. Each Compose or decoration step takes your current skybox, draws the new element on top, and saves the result as the new base image. There is no floating layer stack you can reshuffle later, so the order you apply things in is the order they stack: whatever you add last sits in front of everything before it.
The order to work in
Every skybox follows the same four-stage path. Do them in this order so each step builds on clean work underneath it:
- Create your base — generate from a text prompt, or import your own panorama. This image is the foundation everything else stacks onto.
- Repair the geometry — run Fix Seam (blend the wrap) and Fix Zenith (flatten the overhead pinch) before you decorate, so every later layer sits on clean, seamless geometry.
- Decorate from far to near — add elements outward from the most distant to the closest, so nearer objects correctly cover whatever sits behind them.
- Export — download the engine-ready file (PNG/cubemap for LDR, .hdr for HDR).
What to apply at each distance (far → near)
Because each layer draws on top of the one before it, add things roughly in distance order — farthest first, nearest last. This is the 'layer level' for each kind of element:
- Farthest — the sky itself — Compose Sky: the atmospheric gradient, base color, and overall sky mood that everything else sits against.
- Far — celestial bodies — Compose Sun and Compose Planet / moons — distant discs placed high in the sky.
- Mid — light in the air — God rays, atmospheric optics (sun dogs, halos, light pillars), auroras, rainbows, arches, and star fields.
- Near — weather & volume — Volumetric clouds and mist (HDR), plus clouds, smoke, dust, and rain/virga weather walls.
- Nearest — foreground objects — Sprite billboards (birds, ships, debris) and any decoration you're using to hide a stubborn seam.
Undo is one step — save your base
Undo only steps back a single action. Atmos Forge keeps one undo slot: it stores the image exactly as it was right before your most recent Compose, and the next Compose overwrites it. It does not keep your original base generation once you've stacked a second edit on top — so if you add something, add another thing, then decide you dislike the first one, you cannot undo all the way back to it. Before you start layering, download/save your base generation (and any later version you're happy with) and treat each saved copy as a checkpoint you can always return to.
Standard (LDR) workflow
Standard skyboxes are regular images with normal brightness. This is where AI generation lives, plus the widest set of decoration tools. The tools below are listed in the order you'll use them: create, repair, then decorate far → near, then export. Export is image-based (PNG), with cubemap export on paid plans.
Best for
- Backgrounds and concept environments
- Prompt-to-skybox generation
- Sprite billboards and the full seam-decoration set
Generate a Skybox
Create · Standard (LDR)
Turn a text prompt into a full 360° environment.
AI generation is the main way to create a skybox from scratch. You describe the scene in words and set a few controls — style, mood, time of day, terrain, and vantage point — and Atmos Forge produces a seamless 2:1 equirectangular image saved to your Gallery. Generation always produces a standard (LDR) skybox.
How to use it
- Open the Generator (home) and write a prompt describing the scene, e.g. 'sunset over a calm ocean with dramatic clouds and a low sun'.
- Set the controls: style/art direction, mood, time of day, terrain, and vantage (where the viewer is standing — ground, hilltop, valley, etc.).
- Pick a quality level: Preview (fast, light on your allowance), Standard, or Ultra (highest quality).
- Click Generate. The result is saved to your Gallery, where you can open it to repair, decorate, or export.
Tips
- Iterate with Preview first. Previews are fast and cost the least — dial in the wording and controls on Preview, then spend a Standard/Ultra render on the version you like.
- Be specific about light. Naming the time of day and where the light comes from ('low sun on the left', 'overcast noon') gives far more predictable results than adjectives alone.
- Match the vantage to your scene. A valley or canyon vantage intentionally fills the upper view with terrain walls; pick a ground or hilltop vantage if you want open sky overhead.
- Avoid contradicting yourself. Asking for 'midnight' and 'golden sunset' in one prompt makes the model split the sky into mismatched halves — choose one lighting story.
- Save the result before you start layering. This is your base — once you stack two edits on top, undo can't get back to it (see Work in layers).
Import a Panorama
Create · Standard (LDR)
Bring your own 2:1 equirectangular image in to enhance.
Upload an existing 2:1 equirectangular panorama to repair the seam, decorate, and export — without generating anything. This becomes your base layer, exactly like a generated skybox. Importing is free: it doesn't spend your render allowance.
How to use it
- Open the Generator (home) and choose Import Panorama.
- Select a 2:1 equirectangular image — PNG, JPEG, or WebP, up to 40 MB. The aspect ratio must be close to 2:1.
- It uploads and saves to your Gallery (the filename becomes the title), then opens in the detail view ready to repair, decorate, and export.
Tips
- Confirm it's a true 2:1 equirectangular panorama. Cropped or non-2:1 images are rejected (the importer accepts roughly 1.7:1 to 2.3:1) and won't wrap correctly.
- Fix the seam first. Imported panoramas often have a visible wrap line — run Fix Seam right after importing, before you decorate.
- Imports are free. Bringing in your own panorama doesn't spend your render allowance; only AI generation does.
- Odd pixel widths are snapped to an even width automatically so the wrap math round-trips cleanly — no action needed on your part.
Fix Seam
Repair · Standard & HDR
Blend away the visible line where the panorama wraps.
A 360° panorama wraps around, so its left and right edges meet at a single vertical line called the seam. If those edges don't match, you'll see a visible seam in the engine. Fix Seam blends the two edges together so the wrap becomes invisible. It works on both standard and HDR skyboxes (the HDR version preserves true HDR values). Run it early — right after creating your base — so every decoration you add later sits on a clean wrap.
How to use it
- Open the Fix Seam page from the nav, or use the seam-fix tool directly on a skybox in the detail view.
- Run the fix. Atmos Forge blends a band across the left/right edges so the colors and detail line up (it also flattens the overhead zenith pinch in the same pass — see Fix Zenith).
- Preview the wrap. If a faint line remains, run it again — a second pass widens the blend.
Tips
- Use the lowest blend width you can get away with. Leave blend strength at 100% and dial the width down — the narrower the blend, the more original detail you keep. Staying under ~4% width typically gives the best results.
- Large mismatches force a wider blend. If the left and right edges have very different terrain or objects, you'll need more blend width, and a noticeable seam will likely remain no matter what.
- When a clean fix isn't possible, hide it with decoration. This is exactly where Seam/Skybox Decoration earns its keep: cover what the blend can't reconcile with smoke, clouds, dust, a rainbow, blended sprites, planets, and similar effects.
- Fix the seam before adding seam-spanning decorations. Effects like rainbows or arches that sit on the seam meridian look best on an already-clean wrap.
- It blends, it doesn't repaint. Fix Seam matches the edges rather than inventing new content, so it preserves sunsets, silhouettes, and detail instead of erasing them.
- Confirm the source is a true 2:1 equirectangular image. A cropped or non-2:1 image can't wrap correctly, and the seam fix can't fully compensate.
- Mind even widths on imports. If an uploaded panorama has an odd pixel width, snap it to an even width first so the wrap math round-trips cleanly.
Fix Zenith
Repair · Standard (LDR)
Flatten the swirl/pinch at the very top of the sky.
In an equirectangular image the entire top row collapses to a single point at the zenith — the spot straight overhead. Any color variation along that row shows up in-engine as a swirling 'pinch' (sometimes called the zenith nipple) directly above the viewer. Fix Zenith samples a thin strip near the top and averages it to a single color, so the overhead sky reads as smooth, open sky. Only the top is touched — the bottom (nadir) is left alone because it's usually ground or terrain you want to keep.
How to use it
- Fix Zenith runs automatically as part of Fix Seam, so a normal seam fix already cleans the pole.
- To apply it on its own, use the standalone flatten-pole/zenith pass on the Fix Seam page.
- Look straight up in the preview to confirm the swirl overhead is gone.
Tips
- Usually you get it for free. A standard Fix Seam already flattens the zenith, so you rarely need to run it separately.
- Skip it when you have intentional overhead detail. If you've placed a sun, planet, or hand-painted feature directly at the zenith, flattening would erase it — leave the pole untouched in that case.
- Only the very top changes. Fix Zenith averages a thin polar strip, so it won't affect your horizon or mid-sky detail.
- Best on open-sky vantages. On a canyon or valley vantage the overhead view is terrain walls, not open sky, so the zenith fix often isn't needed.
Compose Sky
Decorate · Standard (LDR) only
Layer procedural atmosphere, sun, and stars into a sky look.
Compose Sky builds a sky from procedural layers — an atmospheric gradient, an optional sun disc and bloom, and stars — to establish or replace the overall sky mood without an AI render. You pick an atmosphere preset (earth day, sunset, or night, Mars, alien violet or green, airless, or overcast) and choose how it combines with your current image. As the farthest layer, apply it first so celestial bodies and effects sit in front of it. LDR only and free to use.
How to use it
- Open a standard skybox in the detail view and choose Compose Sky.
- Pick an atmosphere preset: earth-day, earth-sunset, earth-night, Mars, alien-violet, alien-green, airless, or overcast.
- Choose how it applies — Above horizon (keep your ground, replace only the sky above the horizon), Replace (overwrite the whole image), Blend (mix with your current image by Blend Strength), or Additive only (keep your colors and just add the sun disc, bloom, and stars).
- Set the sun position (azimuth and elevation) and, on dark presets, the star density. Use Horizon Haze to bias the mid-sky toward the horizon color.
- Apply. It's free — no render allowance is spent.
Tips
- Use Above horizon to keep terrain. To refresh only the sky over an existing landscape, this mode replaces sky above the horizon and leaves your ground intact.
- Apply it first. Compose Sky is the farthest layer — run it before suns, planets, and effects so everything else stacks in front.
- Stars only show on dark presets. Star density applies to night, alien, and airless atmospheres; it has no effect on bright daytime presets.
- Additive only is ideal for adding just a sun, bloom, and stars to an AI-generated sky without repainting its gradient.
Compose Sun
Decorate · Standard & HDR
Add a sun or moon disc with a realistic glow.
Compose Sun places a realistic sun (or bright moon) into your sky — a limb-darkened disc with a soft aureole glow that screens over your background so it never darkens what's behind it. As the sun nears the horizon it automatically dims and reddens (air-mass reddening), matching real sunset behavior. It's a far layer: add it after the sky backdrop but before nearer effects. The same tool works on HDR skyboxes, where the sun can keep true brightness for lighting. Free to use.
How to use it
- Open a skybox in the detail view and choose Compose Sun.
- Position the sun by azimuth and elevation.
- Set its angular size (0.1°–30°), brightness, and color.
- Tune the glow — glow radius and glow intensity control the surrounding aureole. Turn on Glow Only to suppress the hard disc and keep just the atmospheric glow.
- Apply (free). On an HDR skybox you also get an HDR Intensity control — see Compose Sun (HDR).
Tips
- Keep it consistent with your scene's light. Place the sun where the rest of the sky's lighting implies, so shadows and planet phases agree.
- Low suns go red on their own. Drop the elevation near or below the horizon for a sunset look — the air-mass model reddens and dims it automatically.
- Glow Only for an over-the-horizon glow. Set the elevation just below 0° with Glow Only to keep a warm sky glow without a visible disc.
- It screens over your sky, so it brightens rather than replaces — it won't punch a dark hole where the disc sits.
Compose Planet
Decorate · Standard & HDR
Place a procedural planet with surface detail, rings, and glow.
Compose Planet adds a procedural celestial body to your sky — a planet, moon, or gas giant — rendered with surface detail, an optional atmosphere, rings, moons, and a glow halo. Everything is generated procedurally, so you control size, position, lighting, and style directly rather than re-rolling an AI image. It's a far layer: place it against the sky, before nearer atmospheric effects and foreground sprites.
How to use it
- Open a skybox from your Gallery to enter the detail view.
- Choose Compose Planet from the decoration tools.
- Position the planet (azimuth/height), then set its size, surface style, atmosphere, rings, and glow.
- Set the lighting — the planet's lit side faces the light direction; use the phase control to make it a crescent, half, or full disc.
- Apply. If you don't like the result, use Undo and adjust — but remember undo only reverses this one action.
Tips
- Keep it believable with size and placement. One large planet low near the horizon reads as a dramatic 'alien world' shot; a small disc higher up reads as a moon. Multiple huge planets overhead tend to look artificial.
- Glow is additive from the planet's own surface, so a dark (unlit) side can still carry a faint rim glow — useful for an eclipse look without lighting the whole disc.
- Rings and moons extend beyond the planet's edge; leave room around the body so they aren't clipped by other elements.
- Use the phase control for mood. A thin crescent with the lit edge facing your scene's sun direction keeps the lighting consistent with the rest of the sky.
Seam Decorations
Decorate · Standard (LDR)
Arches, halos, auroras, rainbows, godrays, weather, and more.
Seam Decorations are a family of procedural effects you place onto the panorama to add atmosphere — and to hide a seam the blend couldn't fully fix. Kinds include rainbows, solid arches, glowing halos, auroras, nebulae, god rays, atmospheric optics (sun dogs, light pillars, 22° halos), clouds (including contrails), mist, smoke, meteors, and weather walls (rain, virga, dust, ash). Each kind has its own placement and intensity controls. These are mid-to-near layers: add them after celestial bodies. Every kind is procedural and free — no render allowance is spent.
How to use it
- Open a skybox in the detail view and choose Seam/Skybox Decoration.
- Pick the effect kind (rainbow, arch, halo, aurora, god rays, optics, clouds, mist, smoke, meteors, or weather).
- Choose the intent: Distract (recommended) lets you aim the effect anywhere via azimuth; Hide locks it to the seam and adds a sky-matched curtain to cover a stubborn wrap line.
- Set placement and shape — latitude/offset, band width, and (for vertical-ribbon kinds) how high it rises — plus opacity, glow, and color.
- Apply (free). Use Undo to adjust, remembering undo only reverses this one action.
Tips
- Use Hide to cover a seam, Distract to decorate. Hide seam-locks the effect and paints a matching curtain over the wrap; Distract draws the eye elsewhere and can be aimed freely.
- Keep the rise below ~0.85. Pushing a vertical ribbon all the way to the top can introduce a swirl at the zenith — stop short of the pole unless you've already flattened it.
- Layer order matters. Add these after suns and planets so the celestial bodies sit behind the atmospheric effects.
- Pick the right tool for a seam. Rainbows and arches sit on the seam meridian and read best on an already-clean wrap; clouds, smoke, and dust are best for covering a mismatch the blend can't reconcile.
- For volumetric realism on HDR skies, prefer Volumetric Clouds & Mist over the flat cloud/mist decorations.
Compose Sprite
Decorate · Standard (LDR) only
Place transparent billboards — birds, clouds, objects.
Compose Sprite drops transparent billboards into your sky — birds, clouds, ships, distant skylines, debris, and more. Sources are the built-in library, your own PNG/WebP upload, or an AI-generated sprite from a text prompt. You place and size each billboard and can color-match it to the surrounding sky so it sits naturally. As the nearest layer, add sprites last so they sit in front of everything else. LDR only.
How to use it
- Open a standard skybox in the detail view and choose Compose Sprite.
- Choose a source: pick from the library, upload your own PNG/WebP (up to 32 MB), or generate one from a prompt.
- If the image has a background, clean it up — Trim BG (free flood-fill for solid backgrounds) or Remove BG (AI cut-out).
- Position it (longitude, latitude, roll) and set its width and height in degrees.
- Use Color Match to harmonize the sprite with the local sky, then Apply.
Tips
- Add sprites last. They're the nearest layer, so place them after the sky, celestial bodies, and atmospheric effects.
- Most of this is free. Placing library sprites or already-transparent uploads and using Trim BG cost nothing — only Generate Sprite and Remove BG (both AI) spend your render allowance.
- Color Match keeps identity. It pulls the sprite toward the local sky colors without fully recoloring it, so the billboard still looks like itself — set it to 0 to leave the sprite untouched.
- Match the sprite to its distance. A billboard reads best when its size and placement fit how far away the object should feel.
Export (Standard)
Export · Standard (LDR)
Download an engine-ready image; cubemap export on paid plans.
When a standard skybox is ready, export it as an image you can import into your engine as a background or panoramic material. Cubemap export (six square faces) is available on paid plans for engines that prefer that format.
How to use it
- Open the finished skybox in the detail view.
- Choose Download/Export and pick the format — a standard equirectangular image, or a cubemap (paid plans).
- Import it into your engine. For step-by-step engine setup (Unity, Unreal, Godot, Blender) and seam-troubleshooting in-engine, see the Export Guide.
Tips
- Disable mipmaps in your engine to avoid a faint in-engine seam — the GPU otherwise samples a lower-resolution level across the wrap. The Export Guide covers the exact settings per engine.
- Use a 2D/panoramic (latitude-longitude) material for equirectangular images; only use the cubemap export when your material expects six faces.
High-dynamic-range (HDR) workflow
HDR skyboxes store true light intensity, so suns and glows stay bright instead of clipping to white — ideal for lighting your scene (image-based lighting). HDR editing tools are float-preserving and free to use. The tools below follow the same order as the standard workflow: import, repair, then decorate far → near, then export. You keep one HDR at a time, and export as .hdr (native to Unity and Unreal).
Best for
- Image-based lighting (IBL) for realistic scene light
- Keeping suns/glows genuinely bright
- Enhancing an existing .hdr panorama
Import an HDR Panorama
Create · HDR
Upload a .hdr file to unlock the HDR-preserving tools.
HDR skyboxes start by importing a .hdr (RGBE) panorama — there's no AI generation for HDR. Once imported, the HDR-preserving tools become available: they decode the true light values, edit in floating point, and re-encode without crushing the highlights. You keep one HDR skybox at a time.
How to use it
- Open the Generator (home) and choose Import HDR.
- Select a 2:1 equirectangular .hdr file. Uploads are capped at 4K (4096×2048).
- It uploads and saves to your Gallery with an HDR badge. Open it to repair and decorate, then export as .hdr.
Tips
- One HDR at a time. HDR files are large, so Atmos Forge keeps a single HDR slot. To start a new one, download or remove your current HDR first.
- Keep it 4K or smaller. Uploads above 4096×2048 are rejected; downscale beforehand if needed.
- Confirm it's genuinely HDR. A .hdr exported from a normal (clipped) image won't have real highlight detail to preserve — start from a true HDR capture or render.
- HDR editing is free. The HDR compose/repair tools don't spend your render allowance, so decorate freely.
Fix Sky Seam (HDR)
Repair · HDR
Blend the wrap seam without crushing HDR values.
Fix Sky Seam is the float-preserving version of seam repair for HDR panoramas. It blends the left and right edges in linear light, so a bright feature sitting on the seam (like a sun or glow) keeps its true HDR intensity instead of being crushed. Run it right after import, before decorating, just like the standard workflow. Free to use.
How to use it
- Open your HDR skybox in the detail view and choose Fix Sky Seam.
- Set the blend width (how far the blend reaches in from each edge) and the blend strength.
- Apply. It edits the .hdr in place and is free — no render allowance is spent.
Tips
- Keep the blend width as low as you can. A narrower blend preserves more original detail; widen it only if the two edges differ a lot.
- Run it before decorating. The fix repaints the edge bands, so do it before placing planets or decorations on the seam, or it may overwrite them.
- It preserves highlights. Because it works in linear float, a sun or glow on the seam stays bright instead of clipping.
- Leave strength at 100% and tune the width — that's usually the cleanest result.
Adjust Exposure
Repair · HDR
Brighten/darken and deepen shadows in true linear light.
Adjust Exposure shifts the overall brightness of an HDR sky and deepens its shadows while keeping the floating-point highlight detail your engine uses for lighting. Because it works in linear float, bright features (suns, nebula cores) stay above the white point and keep driving image-based lighting even when you darken the background. A global adjustment — set the base brightness before stacking decorations on top. Free to use.
How to use it
- Open your HDR skybox in the detail view and choose Adjust Exposure.
- Set Brightness (a radiance multiplier, roughly 0.05×–4×) to make the whole sky brighter or darker.
- Use Shadow Crush (black point) to subtract a floor from the darker areas — it's applied before the brightness gain, so it deepens hazy shadows and makes bright features pop.
- Apply. It rewrites the .hdr radiance and is free.
Tips
- Crush shadows before adding stars. A little Shadow Crush cleans low-level haze so an additive star field reads much cleaner on top.
- Highlights never clip. Brightening won't blow out your sun to flat white the way an LDR exposure would — the high end stays in float.
- It changes what the engine sees. This edits the real .hdr radiance, so it affects both the look and the lighting it casts.
- Set it early. Exposure is global, so dial in the base brightness before you layer decorations.
Star Field
Decorate · HDR
Scatter realistic stars across the upper sky.
Star Field scatters a procedural field of stars across the upper sky with controllable density and brightness. The stars are distributed by solid angle (weighted by latitude) so they stay evenly spaced instead of bunching at the poles, and they're added in float — push the brightness above 1 and the brightest stars become genuinely emissive. As the farthest decoration, add stars before suns, planets, and nearer effects. Free to use.
How to use it
- Open your HDR skybox in the detail view and choose Star Field.
- Set Density (0–1) for how many stars appear and Brightness (0–10×) for how bright they are.
- Change the Seed to get a different random arrangement at the same density.
- Apply (free).
Tips
- Push brightness above 1 for emissive stars. Values over 1× make the brightest stars carry true HDR radiance instead of capping at white.
- Stars are evenly spread. The distribution is solid-angle weighted, so you won't get a dense clump overhead.
- Crush the shadows first. Running Adjust Exposure's Shadow Crush before the stars removes background haze so the additive pass looks cleaner.
- They survive mipmaps. Stars are splatted as soft blobs so they don't disappear when the engine downsamples the texture.
Compose Sun (HDR)
Decorate · HDR
A sun bright enough to actually light your scene.
Compose Sun (HDR) places a sun whose intensity is preserved well above the normal white point, so it actually drives image-based lighting instead of clipping to flat white. It's the same realistic sun model as the standard tool — limb-darkened disc, forward-scatter aureole, and air-mass reddening near the horizon — but composited with unclamped additive blending so the sun keeps its physical energy in the exported .hdr. A far layer: add it before nearer volumetrics so clouds and mist can scatter its light. Free to use.
How to use it
- Open your HDR skybox in the detail view and choose Compose Sun.
- Position the sun (azimuth and elevation) and set its angular size.
- Set HDR Intensity (roughly 1×–50×) — this is what makes the sun bright enough to light your scene in-engine.
- Tune color, brightness, and the glow (radius and intensity); use Glow Only to keep the aureole without the hard disc.
- Apply (free).
Tips
- Crank HDR Intensity for real lighting. A sun at 1× looks white but barely lights an IBL scene — push it well above that so it casts meaningful light in Unity/Unreal.
- Place the sun before volumetrics. Clouds and mist scatter from the sun direction, so set the sun first for convincing bright edges and a god-ray feel.
- Below-horizon glow. Drop the elevation under 0° with Glow Only for a just-set lighting glow with no visible disc.
- It's additive, not screened. Unlike the LDR sun, the HDR sun adds unclamped energy so its true intensity survives into the .hdr export.
Compose Planet (HDR)
Decorate · HDR
A procedural planet that keeps true HDR brightness.
Compose Planet (HDR) is the float-preserving version of the procedural planet compositor — surface, atmosphere, rings, moons, and glow composited in true linear light. It's ray-marched with realistic shading (diffuse light, a Fresnel rim, specular highlights, and atmospheric scattering), and an HDR Intensity control multiplies the planet's emitted glow without changing its coverage. A far layer, placed against the sky before nearer effects. Free to use.
How to use it
- Open your HDR skybox in the detail view and choose Compose Planet.
- Choose the surface type (gas giant, rocky moon, earth-like, etc.), pattern, and color tints. You can also upload a custom surface texture (up to 32 MB).
- Position it (longitude, latitude) and set angular size, rotation, and tilt.
- Set the atmosphere (intensity, thickness, color) and the phase — automatic (lit by your sun) or an override from full to new.
- Use HDR Intensity (roughly 1×–50×) to make any glow/emissive part genuinely bright, then Apply (free).
Tips
- Phase should match your sun. Leave phase on automatic, or if you override it, keep the lit edge facing your scene's sun direction.
- HDR Intensity affects glow, not size. It multiplies emitted radiance without changing the disc's coverage, so a bright rim glow won't grow the planet.
- Leave room for rings and moons. They extend past the planet's edge — keep space around the body so they aren't clipped.
- Place it before nearer effects. As a far layer, compose the planet before volumetrics and weather.
HDR Seam Decorations
Decorate · HDR
Arches, halos, auroras, god rays, and more — HDR-aware.
HDR Seam Decorations are the same family of procedural effects as the standard set, composited in float. The emissive/geometric kinds — arch, halo, aurora, god rays, and atmospheric optics — are HDR-aware: their glow can exceed the white point and contribute to image-based lighting. A few kinds (rainbow, nebula, clouds, mist, meteors, smoke, and weather) are always composited at standard brightness regardless of the HDR intensity. These are mid-distance layers. Free to use.
How to use it
- Open your HDR skybox in the detail view and choose Decorate.
- Pick the effect kind. For true HDR glow that lights your scene, use the emissive kinds: arch, halo, aurora, god rays, or optics.
- Choose orientation — vertical (hugging the seam) or horizontal (a dome/ring) — and set the band width and the kind-specific controls (god rays add ground reach, fan spread, and grain).
- For the HDR-aware kinds, set the HDR intensity to push the glow past white, then Apply (free).
Tips
- Only some kinds carry true HDR brightness. Arch, halo, aurora, god rays, and optics can exceed 1.0 and contribute to lighting; rainbow, nebula, clouds, mist, meteors, smoke, and weather stay at standard brightness even with the intensity raised.
- Fix the seam first. Run Fix Sky Seam before placing seam decorations, or the fix will repaint the edge over your work.
- Additive effects can read very bright over an already-bright sky — that's expected, not a bug.
- For realistic clouds/mist on HDR skies, use Volumetric Clouds & Mist instead of the flat cloud/mist decorations here.
Volumetric Clouds & Mist
Decorate · HDR only
Realistic light-scattering clouds, mist, nebula, and aurora.
Volumetric HDR adds true 3D, light-scattering atmosphere — clouds, mist, nebula, or aurora — rendered by a single-scattering ray-marcher. Because forward-scattered sunlight pushes well past the normal white point, this is HDR-only: it has no standard (LDR) equivalent. The result reads as real depth and glow rather than a flat overlay. As a near layer, add it after your sun and distant elements.
How to use it
- Open an HDR skybox in the detail view.
- Choose Volumetric HDR and pick the type: clouds, mist, nebula, or aurora.
- Set the position/origin and adjust density, height, and scattering.
- Apply. Like the other HDR tools, this is free and doesn't spend your render allowance.
Tips
- Place your sun first. Clouds and mist scatter light from the sun direction, so adding the sun (or setting the light) before the volumetrics gives convincing bright edges and god-ray feel.
- Don't over-fill. High density across the whole sky flattens the effect; leave gaps so the depth and backlighting read.
- Clouds/mist here are HDR-only. The flat 'clouds'/'mist' seam-decoration billboards are a separate LDR feature — for HDR skies, prefer this volumetric tool for realism.
- Nebula and aurora are emissive. They glow on their own rather than scattering the sun, so they work even in a dark, sunless sky.
Export .hdr
Export · HDR
Download a .hdr that Unity and Unreal import natively.
HDR skyboxes export as a .hdr (RGBE) file that preserves true light intensity. Both Unity and Unreal import .hdr natively as an environment/skybox texture, so you can use it as a background and as an image-based lighting source.
How to use it
- Open the finished HDR skybox in the detail view.
- Choose Download/Export — HDR exports as a .hdr file.
- Import it into your engine as an environment/HDRI texture. For engine-specific setup and lighting tips, see the Export Guide.
Tips
- Use it for lighting, not just background. Assign the .hdr to your engine's sky/environment light so the scene picks up real color and intensity from the sky.
- Round-trip is float-accurate. A tiny per-channel difference is normal RGBE encoding behavior, not a quality loss — the highlight detail your lighting needs is preserved.
- Export .hdr only. Atmos Forge ships the .hdr format specifically because Unity and Unreal both import it directly; there's no separate HDR cubemap step.