Shadows and glows

Six effects darken or lighten an object's edges. Their numbers are InDesign's: Size is the width of the soft band, Spread and Choke are percentages of it, and Angle says where the light comes from.

In short A drop shadow is offset by XOffset and YOffset; an inner shadow, a satin and a bevel by an Angle and a Distance, where the angle names the direction of the light, so the shadow falls the opposite way. Size is how wide the soft edge is, not a blur radius: an outer shadow or glow has faded to about a sixth of its strength Size / 2 beyond the object's edge and is nearly gone at Size. Spread (outer effects) and ChokeAmount (inner effects) are percentages of Size that harden the edge. The drop shadow is on with Mode="Drop", the others with Applied="true".

How InDesign reads the numbers

These rules were measured by having InDesign draw each effect and comparing its output with the values in its own IDML.

• Size is the width of the band. For effects that spill outside the object (drop shadow, outer glow) the edge is a Gaussian falloff with a standard deviation of Size / 2: at Size / 2 outside the outline about 16 % of the strength is left, at Size about 2 %. Effects that stay inside the object (inner shadow, inner glow) fall off with a standard deviation of about 0.4 × Size. Reading Size as the blur radius doubles the softness.
• Spread and ChokeAmount are percentages of Size. Spread grows the shape outward before the falloff; choke moves the edge inward. Neither is a distance in points.
• Angle names the light. It is measured in degrees counter-clockwise from the right, and the shadow falls away from the light: with y pointing down the page, the offset is x = −Distance × cos(Angle) and y = +Distance × sin(Angle). InDesign's default, 120°, puts the light at the upper left and the shadow down and to the right.
• A drop shadow's offset is written as XOffset and YOffset. Positive is right and down. Inner shadows and satins are written with Angle and Distance.
• UseGlobalLight="true" takes the angle from the document's light, GlobalLightAngle (and for a bevel GlobalLightAltitude) on <TransparencyPreference>. It is false in every surveyed file.

Opacity is a percentage of the effect's strength, Noise a percentage of grain, and EffectColor names a palette colour; n leaves the effect's default colour.

Drop shadow

On with Mode="Drop", off with Mode="None". InDesign's default is a black, 75 %-opaque Multiply shadow, 7 pt right and 7 pt down, Size 5. KnockedOut="true" hides the shadow behind a semi-transparent object; HonorOtherEffects lets other effects shape the shadow. In the surveyed documents, drop shadows are switched on in 10.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<idPkg:Spread xmlns:idPkg="http://ns.adobe.com/AdobeInDesign/idml/1.0/packaging" DOMVersion="20.0">
  <Spread Self="uspread" PageCount="1" BindingLocation="0" ShowMasterItems="true" AllowPageShuffle="true" ItemTransform="1 0 0 1 0 0">
    <Page Self="upage" Name="1" AppliedMaster="umaster" ItemTransform="1 0 0 1 0 0" GeometricBounds="0 0 841.89 595.276" MasterPageTransform="1 0 0 1 0 0"/>
    <Rectangle Self="urect" ItemTransform="1 0 0 1 140 260" FillColor="Color/Teal" StrokeColor="Swatch/None" StrokeWeight="0">
      <Properties>
        <PathGeometry>
          <GeometryPathType PathOpen="false">
            <PathPointArray>
              <PathPointType Anchor="0 0" LeftDirection="0 0" RightDirection="0 0"/>
              <PathPointType Anchor="0 180" LeftDirection="0 180" RightDirection="0 180"/>
              <PathPointType Anchor="300 180" LeftDirection="300 180" RightDirection="300 180"/>
              <PathPointType Anchor="300 0" LeftDirection="300 0" RightDirection="300 0"/>
            </PathPointArray>
          </GeometryPathType>
        </PathGeometry>
      </Properties>
      <TransparencySetting>
        <DropShadowSetting Mode="Drop" BlendMode="Multiply" Opacity="75" XOffset="12" YOffset="12" Size="10" EffectColor="Color/Black" Spread="0" Noise="0" KnockedOut="true" UseGlobalLight="false" HonorOtherEffects="false"/>
      </TransparencySetting>
    </Rectangle>
    <TextFrame Self="uframe" ParentStory="ustory" PreviousTextFrame="n" NextTextFrame="n" ContentType="TextType" AppliedObjectStyle="ObjectStyle/$ID/[None]" Visible="true" Name="$ID/" ItemTransform="1 0 0 1 57.638 145.8237" FillColor="Swatch/None" StrokeColor="Swatch/None" StrokeWeight="0">
      <Properties>
        <PathGeometry>
          <GeometryPathType PathOpen="false">
            <PathPointArray>
              <PathPointType Anchor="0 0" LeftDirection="0 0" RightDirection="0 0"/>
              <PathPointType Anchor="0 400" LeftDirection="0 400" RightDirection="0 400"/>
              <PathPointType Anchor="480 400" LeftDirection="480 400" RightDirection="480 400"/>
              <PathPointType Anchor="480 0" LeftDirection="480 0" RightDirection="480 0"/>
            </PathPointArray>
          </GeometryPathType>
        </PathGeometry>
      </Properties>
    </TextFrame>
  </Spread>
</idPkg:Spread>

What casts the shadow

A drop shadow is cast by what the object paints. InDesign follows these rules for every kind of shape:

• A filled shape casts the shadow of its outline, grown by the part of a visible stroke that lies outside the outline. A rounded rectangle casts a rounded shadow, an ellipse an elliptical one.
• A shape with no fill and a visible stroke casts the shadow of its stroke band only.
• A line casts the shadow of its stroke, at the stroke's width, with its caps.
• A text frame with no fill casts the shadow of its text, glyph by glyph.

A shadow inside StrokeTransparencySetting is cast by the stroke alone; one inside ContentTransparencySetting by the content alone.

In Paged: drop shadows are drawn for rectangles, ovals, polygons, lines and text frames by these rules, matched to InDesign on test pages for lines, ovals, polygons and rectangles. A group's shadow is drawn for the group as a whole. A shadow at the stroke level is kept as the stroke's shadow; one at the content level is not drawn.

Supported · verified

Inner shadow

A shadow inside the object's edge, as if the object were cut out of the page. Positioned by Angle and Distance (default 120° and 7 pt), softened by Size, hardened by ChokeAmount. Default Multiply, 75 %.

In Paged: inner shadows are drawn by the rules above, the light angle included.

Supported · verified

Outer glow and inner glow

A glow is an unoffset band of colour around the outside of the edge (outer) or inside it (inner). Size sets its width, Spread hardens it. Inner glows spell their choke Spread too. Source on an inner glow is EdgeSourced (from the edge inward) or CenterSourced (from the centre outward). Technique is Softer in every surveyed file. The default blend mode is Screen, which lightens; a black glow under Screen draws nothing.

In Paged: both glows are drawn; a glow whose EffectColor does not resolve is drawn white, a shadow black. Supported · verified

Bevel and emboss

Shading that makes the object look raised or sunk. Style chooses the kind (InnerBevel by default), Technique the profile (SmoothContour, ChiselHard, ChiselSoft), and Direction (Up by default) whether it is raised or sunk. The light comes from Angle at the height Altitude. The facet is Size wide; Depth, a percentage that can go far above 100, makes it steeper rather than scaling the result; Soften blurs it. The highlight and shadow each have a colour, an opacity and a blend mode (Screen and Multiply by default).

In Paged: bevels are drawn with a facet Size wide, shaded against the light. Where the facet is wider than half the object, InDesign fades it and Paged does not yet.

Supported · verified

Satin

A soft, inner shading made of two offset copies of the shape: Angle and Distance set the offset, Size the softness, InvertEffect swaps the light and dark areas. Default Multiply, 50 %.

In Paged: satin is drawn from two offset, softened copies of the shape; it is not yet matched to InDesign as closely as the other effects. Parsed, partly rendered

Stacking

An outer glow and a drop shadow are drawn beneath the object; the inner effects (inner shadow, inner glow, bevel, satin) are drawn on top of its fill.

Frequently asked questions

Is Size a blur radius? No. It is the width of the soft band. Outer effects fall off with a standard deviation of Size / 2, inner effects about 0.4 × Size.

Which way does a shadow fall for Angle="120"? Down and to the right. The angle names where the light is, counter-clockwise from the right, and the shadow falls the opposite way.

Are Spread and ChokeAmount in points? No. They are percentages of Size.

How is a drop shadow's offset written? As XOffset and YOffset in points, positive right and down.

Does a frame with no fill cast a shadow? Yes, from what it does paint: its stroke band, or, for a text frame, its text.

How do I tell whether an effect is on? A drop shadow is on with Mode="Drop"; the other effects here with Applied="true". InDesign writes the settings even when the effect is off.