Tutorials · Light and Shadow · Chapter 13

Glow

30 minutes Uses: PostVolume

By the end

A Global Post Volume, look, with a bloom at Threshold 0.4, Intensity 1.6 and Spread 4
What Exposure, Tint, Saturation and Vignette do
A Box Post Volume, draught, at the door: Bounds, Blend and Priority, and the film controls
Why Blur Pairs above 2 change nothing here, and why the light does not band

On this page

A look for the whole hall
Exposure, tint, saturation, vignette
Bloom
A second look, at the door
Smooth light
The glow
Check it works

Reference

PostVolume

A look for the whole hall

A Post Volume grades the whole picture once it is lit: its brightness and colour, its corners, and a glow on whatever is brightest. Without one the hall is drawn as the lights leave it. Effects and shaders has the whole component; this chapter gives the hall one.

Select Hall, press + Add node, and choose Post Volume. Rename it look.
Set its Position to 320 and 180, the middle of the view.
Set Area to Global. Leave Bounds at 1920 by 1080, Blend at 64 and Priority at 0.
Open Profile. Set Exposure to 1.0, Tint to 1.0, 0.97, 0.92, Saturation to 1.0 and Vignette to 0.45.
Under them, the Enabled below Vignette is the bloom’s switch. Keep it ticked, and set Threshold to 0.4, Intensity to 1.6, Blur Pairs to 2 and Spread to 4.0.
Keep Aberration at 0, Grain at 0 and Grain Rolloff at 0.85.
Press Ctrl+S.

The whole hall as chapter 12 left it: the first lantern’s bricks warm at the left, the window white with a sharp edge, a green wash round the third lantern, the stained glass on the floor, a timber leaning on the right pillar, and a pale shaft in the doorway at the right, with no glow — Before: the hall as chapter 12 left it.

The same hall with the look: the window glowing past its edges in a soft white halo, the corners a little darker and the colours a little warmer, the timber and the doorway’s shaft as before — After: the window glows, the corners darken a little, the colours warm.

Enabled: Whether this volume grades the picture at all. Unticked, it grades nothing wherever the camera stands: the hall as chapter 12 left it, above, is the hall with it unticked. A new volume starts ticked, and look stays ticked. The bloom has an Enabled of its own, further down.
Area: Global, everywhere, or Box, only inside Bounds. A Box blends in at its edge, so a room can have its own look. look is Global.
Bounds, Blend: A Box’s size in world units, and how far inside its edge it reaches full strength: 0 cuts, 64 is about a doorway. A Global volume reads neither, so they stay at 1920 by 1080 and 64.
Priority: Which volume wins where two overlap: the higher one is folded in on top. 0 here, with only one.
Profile: The look itself: twelve fields that open under it, Exposure to Grain Rolloff, set one by one in the sections below. A volume brings its whole Profile, not only the fields you changed, so a field left at its default pulls the picture to that default wherever the volume applies.

Exposure, tint, saturation, vignette

Exposure: How bright the whole picture is, as a multiplier. 1 leaves it as lit; 1.0 here.
Tint: A colour the whole picture is multiplied by, three numbers from 0 to 1 and no alpha. 1.0, 0.97, 0.92 takes a little blue and a little green out of everything, so the hall reads warmer.
Saturation: How strong the colours are. 1 leaves them as lit and 0 is grey; 1.0 here.
Vignette: How much darker the corners get, from 0, none, to 2. 0.45 here. It costs nothing either way.
Aberration, Grain, Grain Rolloff: Film effects, all off here. Aberration pulls the colour channels apart at the edge of the picture, in pixels; Grain adds noise, from 0; Grain Rolloff, from 0 to 1, is how far the noise backs off as a pixel nears white. 0, 0 and 0.85: the grain is off, so its rolloff is unread. The draught, below, turns them on.

The same hall with Vignette 0: the corners as bright as the middle, the window’s glow as before, the timber and the doorway’s shaft as before — For comparison, Vignette `0`.

Bloom

Bloom is the glow round something bright: the picture is blurred, and what was brightest is added back over it. The window is the brightest thing in the hall, so it is what glows.

Enabled, the bloom’s: Its own switch, below Vignette. The Enabled at the top of the component switches the whole volume.
Threshold: How bright a pixel must be to glow, from 0 up. A pixel gives up the part of its brightness above this. At 0.4 a white window gives up three fifths of itself, and glows well; at 0.8 it gives up a fifth, and its halo nearly goes. 0.4 here.
Intensity: How strongly the glow is added back, from 0 up. 1.6 here; the default is 0.8.
Blur Pairs: How many rounds of blur the glow gets, from 0 to 7. Each pair is two passes of the picture. 2 here.
Spread: How far each blur reaches, from 1, the plain blur, to 8. It widens the glow without drawing any more. 4.0 here. It wants two Blur Pairs or more to stay smooth.

The window glass and the arch round it at Spread 1: a thin glow hugging the glass, the white of the panes, and the third lantern on the wall at the right — For comparison, Spread `1`: the glow hugs the glass.

The same view at Spread 4: a wide soft halo round the whole window, reaching well past the glass into the arch — Spread `4`, the value you set.

The same view at Threshold 0.8: the window’s panes cream rather than white, and the halo round it thin and faint — For comparison, Threshold `0.8`: far less of the window’s brightness feeds the glow, so the halo nearly goes.

A second look, at the door

A Global volume grades everywhere. A Box grades by where the camera stands: the whole picture takes the look of the box the camera is in, faded in across the box’s edge. The real case is a room with a look of its own, such as a cold draught by the doorway, which a camera following a player to the door fades into.

Select Hall, press + Add node, and choose Post Volume. Rename it draught.
Set its Position to 560 and 180, Area to Box, Bounds to 192 and 400, Blend to 48 and Priority to 1.
Open Profile. Set Exposure to 1.03, Tint to 0.76, 0.83, 1.0, Saturation to 0.6 and Vignette to 0.6.
Keep the bloom’s Enabled ticked, and set Threshold to 0.4, Intensity to 1.6, Blur Pairs to 2 and Spread to 4.0, as in look.
Set Aberration to 3, Grain to 0.04 and Grain Rolloff to 0.6.
Press Ctrl+S, then F5: the hall looks as it did, because the camera stands outside the draught. Press F5 again to stop.

Press Frame in the toolbar to fit the whole box in the Viewport. A selected Box shows its Bounds as a rectangle with a handle at each corner, which you drag to resize it, and a second rectangle inside, where the volume reaches full strength. The handle on that inner rectangle’s right edge drags the Blend. The Viewport is graded by the draught here, because the view stands inside it.

Area Box: The volume applies only where the camera is inside its Bounds, centred on the node, and fades in across its edge.
Bounds: The rectangle, in world units, centred on the node: 192 by 400 here, the doorway’s end of the hall from top to bottom.
Blend: How far inside its edge the volume reaches full strength, in world units, from 0. At the edge it applies not at all, 48 units in it applies fully, and between them it fades in, so halfway in is half its look. 0 cuts at the edge. Outside the edge a volume changes nothing, whatever its Profile holds.
Priority: Where two volumes apply, the higher is folded in on top of the lower. 1, over the look’s 0, so the draught is on top where both apply.

The whole hall with the camera outside the draught, the same as the hall with the look: the window glowing in a soft white halo, the first lantern’s bricks warm, a green wash round the third lantern, a timber leaning on the right pillar and a pale shaft in the doorway — As you left it: the camera outside the draught, the hall as the look grades it.

The hall with the draught slid so the camera is in its blend band: darker and cooler than the look alone, the colours drained part of the way toward grey, fine grain over the dark, the lanterns’ bricks dimmer and the window still glowing — For comparison, the draught slid so the camera stands `24` units inside its edge, half its Blend: half its look.

The hall with the draught slid round the camera: the whole picture dark, cold and nearly grey, the greens and browns drained, thick grain over the dark, a faint red and blue fringe at the edges, the first lantern’s bricks a dim grey-brown and the window still glowing white — For comparison, the draught slid round the camera: all of its look.

The hall with the draught round the camera but its Priority at -1: the same warm look as the picture with no draught, the window glowing in a soft halo and the lanterns’ bricks warm, with no grain and no grey — For comparison, round the camera with its Priority at `-1`: the look, folded in after it at full weight, replaces it.

The toolbar tells you which volume is winning where the camera stands, and how much of it applies.

With the camera in the band, the toolbar names the volume winning there and how much of it applies: draught 0.50.

Film: aberration and grain

Saturation: The draught’s 0.6 keeps three fifths of the colour and drains the rest toward grey: a cold night’s look.
Aberration: How far, in pixels, the red and blue parts of the picture pull apart at its edge, from 0. It is nothing at the middle and widest in the corners, as in a lens. 3 here is a plain fringe; ten would be a blow.
Grain: Noise over the whole picture, new every frame, as on film: a fraction of the full range, from 0. 0.04 is faint, plainest in the dark; by 0.3 the dark is all noise.
Grain Rolloff: How far the grain backs off as a pixel gets brighter, from 0 to 1. At 0 every pixel gets all of it, and at 1 a white pixel gets none. 0.6 here. A pixel already past white, like the window’s panes with the bloom on them, shows no grain at any Rolloff.

The first lantern and its bricks near the picture’s left edge at Aberration 0: the lantern’s glass pale cream and sharp-edged with no coloured fringe, and grain over the bricks and the dark round them — For comparison, Aberration `0`.

The same view at Aberration 3: the lantern’s glass edged with a red fringe on its left and a blue-green one on its right, a faint fringe along the brick joints too, the bricks and the grain as before — Aberration `3`: the first lantern’s glass fringed red and blue near the picture’s edge.

The window’s panes and the dark round them with Grain 0: the dark smooth, the panes white with a soft glow — For comparison, Grain `0`.

The same view at Grain 0.04: a fine speckle over the dark round the window and the arches, the panes as white as before — Grain `0.04`, the value you set: faint grain, in the dark; the panes stay clean.

The doorway’s glow and the floor before it with Grain 0.3 and Grain Rolloff 0: the dark thick with noise and the pale glow of the doorway just as noisy, its bright middle speckled — For comparison, Grain raised to `0.3` so the difference shows, with Grain Rolloff `0`: the doorway’s glow as grainy as the dark.

The same view with Grain Rolloff 1: the dark as noisy as before, but the doorway’s bright middle smooth, the grain fading out toward the brightest part of the glow — For comparison, Grain `0.3` with Grain Rolloff `1`: the glow’s bright middle clean.

Smooth light

The hall’s light is worked out in a light buffer before it reaches the picture. On a computer that buffer holds numbers past 1 in fine steps, a format called Float16, so lights add past the paint and a dim fade stays smooth. A phone’s tier uses the screen’s own eight bits: a dim fade breaks into visible steps, called banding, and light past 1 is cut off. The Render menu names the buffer in its Light buffer row.

The Render menu open: Post set to Game with the line look 1.00 under it, Preview as Desktop, Android and Android Low with a count of 7 passes, Anti-aliasing Off, View Shaded, a dimmed Light buffer row with Float16 chosen and a White point of 1.00, the line Game runs the light buffer of the project’s quality tier, and Lights as authored — Render → **Light buffer**: in Game it shows the tier’s buffer, Float16 on a computer, and is not yours to change there.

There is nothing to set here: Game shows the buffer of the project’s own tier and dims the row. Chapter 14 previews the phone tier, where the eight-bit buffer is.

The glow

The look

Field	Value
Area	Global
Bounds, Blend, Priority	`1920` by `1080`, `64`, `0`
Exposure	`1.0`
Tint	`1.0`, `0.97`, `0.92`
Saturation	`1.0`
Vignette	`0.45`
Bloom Enabled	ticked
Threshold	`0.4`
Intensity	`1.6`
Blur Pairs	`2`
Spread	`4.0`
Aberration, Grain, Grain Rolloff	`0`, `0`, `0.85`

The draught

Field	Value
Position	`560`, `180`
Area	Box
Bounds	`192` by `400`
Blend	`48`
Priority	`1`
Exposure	`1.03`
Tint	`0.76`, `0.83`, `1.0`
Saturation	`0.6`
Vignette	`0.6`
Bloom	as the look’s: Enabled ticked, Threshold `0.4`, Intensity `1.6`, Blur Pairs `2`, Spread `4.0`
Aberration	`3`
Grain	`0.04`
Grain Rolloff	`0.6`