indd-utils/docs/format/transparency.md

Transparency

Implemented in src/idml/transparency.rs.

Page items keep their transparency settings in their attribute list (chunk 0x6E03, see attributes.md), with attribute IDs in two ranges: 0x108xx and 0x1EBxx. Object styles keep a full list of the same attributes in chunk 0x1B92C (u16 count, then records).

IDML writes them as child elements of the page item or object style: TransparencySetting (the whole object), StrokeTransparencySetting and FillTransparencySetting, each holding one element per effect (BlendingSetting, DropShadowSetting, InnerShadowSetting, GradientFeatherSetting, ...).

How the mapping was checked

IDML writes a setting on a page item only when it differs from the item's object style. So each INDD value was compared with the value in effect:

1. the value written on the IDML item, if there is one;
2. otherwise the value of its object style, following BasedOn;
3. otherwise the default in Resources/Preferences.xml (TransparencyDefaultContainerObject).

The tables count page items of the pairs whose IDML is from the same InDesign version as the INDD. "On the item" means the IDML item states the value itself, which is the evidence that tells the attribute apart. The 576 object styles of the pairs (matched by name) agree with their IDML style on every attribute below.

Values equal to the object style

The converter writes only the values that differ from the object style's (its chunk 0x1B92C, then the styles it is based on), and an effect element only when it has such a value or its opacity stops differ from the style's. Per effect element the converter wrote before this rule, over the 489 trustworthy pairs (D = the attributes whose value differs from the style's effective value; style values followed through BasedOn, then TransparencyDefaultContainerObject):

Element	D empty, IDML writes nothing	D empty, IDML writes it	D not empty, IDML writes exactly D or more
GradientFeatherSetting	6,251	53	2,604
InnerShadowSetting	2,884	0	17
DropShadowSetting	44	8	289
BlendingSetting	1	0	1,616

Where IDML writes more than D (349 elements), the converter already wrote those values. The 53 + 8 elements with D empty that IDML still writes are not explained.

Object transparency (TransparencySetting)

The drop shadow rows of 0x1081B, 0x1081C, 0x1081E, 0x1081F and 0x1084A come from the items of the 1,251 trustworthy pairs of the corpus after 2026-10 that have a DropShadowSetting in IDML, groups included: each ID is the only one whose value equals the IDML value in every item where both exist (after resolving the value through the object style, as below). In the item list 0x1081F is the drop shadow's blend mode; in the document preference list the same number is BlendingSpace, a separate list. With the write rule below, the converter reproduces over the trustworthy pairs 580 of 580 XOffset and YOffset values, 397 of 397 Opacity, 62 of 62 BlendMode and 3 of 3 Spread, with no extra value.

Comparison with the style. IDML writes an item's value when it differs from the style's in any digit: one 15.0 document has 23 text frames with YOffset 7.000000133081193 and a style value of 7, and IDML writes all 23. Comparing the full text of the values changes nothing else in the transparency settings of the trustworthy pairs.

ID	IDML	Encoding	On the item
0x10816	BlendingSetting/Opacity	f64, percent	57 items in 4 files (40, 49, 50, 57, 69, 70)
0x10817	BlendingSetting/BlendMode	i32 code (below)	56 items in 4 files
0x1081A	DropShadowSetting/Mode	i32: 0 None, 1 Drop	8 items with 1 in 2 files
0x1081F	DropShadowSetting/BlendMode	i32 code (below): 0 Normal, 4 SoftLight seen	89 of 89 items in 16 files
0x1081E	DropShadowSetting/Opacity	f64, percent	424 of 424 items in 78 files
0x1081B	DropShadowSetting/XOffset	f64	649 of 649 items in 88 files
0x1081C	DropShadowSetting/YOffset	f64	649 of 649; 256 of these items have X ≠ Y
0x10820	DropShadowSetting/Size	f64	6 items, two values; 406 of 406 rectangles and text frames over the 654 pairs of the later corpus
0x1084A	DropShadowSetting/Spread	f64, percent	28 of 28 items in 9 files
0x10837	DropShadowSetting/EffectColor	swatch UID	11 of 11 items in 6 files (below)
0x1EB6F	DropShadowSetting/KnockedOut	u16: 1 true, 0 false; true where not stored	30,692 of 30,692 items (below)
0x1084D	InnerShadowSetting/Applied	u16: 1 true, 0 false	10 items with 1
0x1084E	InnerShadowSetting/EffectColor	swatch UID	10 items (below)
0x10852	InnerShadowSetting/Distance	f64	10 items with 0
0x10855	InnerShadowSetting/Size	f64	10 items with 2.83
0x1EB8A	GradientFeatherSetting/Applied	u16: 1 true, 0 false	56 items in 2 files
0x1EB8C	GradientFeatherSetting stops	list (below)	59 items, 170 stops
0x1EB8D	GradientFeatherSetting/Angle	f64	1 item (−90)
0x1EB8E	GradientFeatherSetting/Length	f64	96 items in 3 files
0x1EB8F	GradientFeatherSetting/GradientStart	two f64	96 items in 3 files
0x1EB91	GradientFeatherSetting/HiliteAngle	f64	1 item (−62.2)
0x1EB92	GradientFeatherSetting/HiliteLength	f64	1 item (1)

More IDs, found over the 489 trustworthy pairs before 2026-10 by matching the item's attribute list with the IDML value after resolving the value through the object style, BasedOn and TransparencyDefaultContainerObject (each ID is the only one whose value maps one to one onto the IDML value in all rows):

ID	IDML	Encoding	Items
0x10819	BlendingSetting/IsolateBlending	u16: 1 true	46 of 46
0x10857	OuterGlowSetting/Applied	u16: 1 true	157 of 157
0x10858	OuterGlowSetting/BlendMode	i32 code (below; 0, 1, 3, 9 seen)	79 of 79
0x10859	OuterGlowSetting/Opacity	f64	144 of 144
0x1085B	OuterGlowSetting/EffectColor	swatch UID	73 of 73
0x1085D	OuterGlowSetting/Spread	f64	106 of 106
0x1085E	OuterGlowSetting/Size	f64	172 of 172
0x1085F	InnerGlowSetting/Applied	u16	6 of 6
0x10860	InnerGlowSetting/BlendMode	i32 code (0, 1 seen)	10 of 10
0x10866	InnerGlowSetting/Size	f64	10 of 10
0x108D8	FillTransparencySetting/BlendingSetting/Opacity	f64	6 of 6 (100, 40)

IDML writes OuterGlowSetting and InnerGlowSetting after InnerShadowSetting, as the schema lists them. Not identified: the inner glow's Opacity, Spread and EffectColor and the outer glow's Noise. Drop shadow KnockedOut is 0x1EB6F (below).

All items whose value is not on the IDML item (it comes from the style or the default) match as well: for example 743 items for InnerShadowSetting and the gradient feather attributes, with the default values (Applied="false", Distance="7", Size="7", Length="0").

In pairs whose IDML is from an older version, 14 more items match on opacity and blend mode. One item there has 50 where the IDML says 100; that file was probably saved again after the export.

Values outside the schema's range. Four items in a file without an IDML store a drop shadow size of −2.83; the schema allows 0 to 1000. The converter leaves out any value of the attributes above that is outside the schema's range, with a warning: sizes and distances 0–1000, opacity 0–100, angles −180–180.

Blend mode codes. The code is the position of the value in the IDML schema's BlendMode enumeration (Normal, Multiply, Screen, Overlay, SoftLight, HardLight, ColorDodge, ColorBurn, Darken, Lighten, Difference, Exclusion, Hue, Saturation, Color, Luminosity, from 0). Seen: 1 Multiply (3 items), 3 Overlay (62), 9 Lighten (5), and 0 Normal in all 576 object styles, whose IDML blend mode is Normal; over the 489 trustworthy pairs before 2026-10 also 2 Screen (7 items), 4 SoftLight (10), 5 HardLight (12), 7 ColorBurn (3), 14 Color (3) and 15 Luminosity (7), 42 of 42. The converter writes all sixteen positions.

Inner shadow colour. The 10 items with the effect applied name the swatch that IDML writes as EffectColor. Items without the effect store UID 0xB, where the IDML default is n (no colour). The converter writes the colour only when the effect is applied.

Drop shadow colour. Item attribute 0x10837 is the swatch of the drop shadow, IDML EffectColor. With the write rule above, the converter reproduces all 11 EffectColor values of the trustworthy pairs (8 polygons, 2 rectangles, 1 text frame; swatches such as Color/Paper and named colours), with no extra value. In 7 of these items the object style chain stores 0 for the attribute, which names no swatch, so every item colour differs from it. The one other item whose style stores 0 has the Black swatch, and its IDML has no EffectColor. One item cannot show whether IDML compares with Black or leaves the value out for another reason; the converter leaves out Black when the style stores 0.

Drop shadow knockout. Page item attribute 0x1EB6F is DropShadowSetting/KnockedOut: a u16, 1 true, 0 false (value type 0x6E65). Object styles hold it in their transparency list (chunk 0x1B92C); [None] stores 1, and the styles that store 0 are mostly [Normal Graphics Frame], [Normal Text Frame] and user styles of older documents. The document's base list (class 0x6E02) does not have it. An item or a style chain that does not store it has true, the value of TransparencyDefaultContainerObject in every corpus IDML. IDML writes KnockedOut on the item when this value differs from the style's, by the rule above; an item without an object style gets no value it does not store.

With this rule the converter reproduces, over the trustworthy pairs, every KnockedOut of the items: 17,543 of 17,543 rectangles, 9,505 of 9,505 text frames, 1,911 of 1,911 polygons, 1,578 of 1,578 graphic lines and 155 of 155 ovals. Before the rule, 25, 13, 14, 23 and 8 documents missed these DropShadowSetting elements. It also writes 380 elements that IDML does not have (760 extra values in 3 documents): items that store nothing, whose style stores 0, and whose IDML has no KnockedOut. Nothing stored in the items or their styles separates them from the items that follow the rule; they stay open (unknowns.md).

Not covered: items whose drop shadow is off (Mode="None") for which IDML still writes a DropShadowSetting (the "D empty, IDML writes it" column above).

Stroke and fill transparency

Only the gradient feather has values that tell its attributes apart:

ID	IDML	On the item
0x1EB93	StrokeTransparencySetting/GradientFeatherSetting/Applied	2 items through their style, and the style
0x1EB95	stroke gradient feather stops	2 items
0x1EB96	StrokeTransparencySetting/GradientFeatherSetting/Angle	2 items through their style (90), and the style
0x1EB97	StrokeTransparencySetting/GradientFeatherSetting/Length	4 items in 2 files
0x1EB98	StrokeTransparencySetting/GradientFeatherSetting/GradientStart	4 items in 2 files
0x1EB9C	FillTransparencySetting/GradientFeatherSetting/Applied	10 items, 1 through its style
0x1EB9E	fill gradient feather stops	11 items
0x1EB9F	FillTransparencySetting/GradientFeatherSetting/Angle	10 items (−90)
0x1EBA0	FillTransparencySetting/GradientFeatherSetting/Length	3 items in 2 files
0x1EBA1	FillTransparencySetting/GradientFeatherSetting/GradientStart	3 items in 2 files

The stroke, fill and object gradient feathers of the same item can hold the same length and start, so each ID was taken from items where only one of the three is set (for example 0x1EB97 matches the stroke value in 4 items and the fill value in only 2).

Opacity gradient stops

Value type 0x1085F. A u32 stop count, then three f64 per stop:

Field	Contents
f64	Location, 0–1 (IDML Location in percent)
f64	Position of the midpoint between this stop and the next, 0–1, measured from the start of the gradient; 1 for the last stop
f64	Opacity in percent (IDML Opacity)

IDML writes a Midpoint on every stop but the first: the midpoint between the previous stop and this one, in percent of the distance between them. So for stop i, Midpoint = (midpoint of stop i−1 − location of stop i−1) / (location of stop i − location of stop i−1) × 100. A list with count 0 is stored as a 4-byte value.

All 170 stops of the items above match on Opacity, Location and Midpoint; so do the 5 stops of two object styles. IDML names an item's stops <item>TransparencySetting1GradientFeatherSetting1OpacityGradientStop<i> (with StrokeTransparencySetting or FillTransparencySetting for those settings), 170 of 170.

Object styles

Chunk 0x1B92C of an object style holds the transparency attributes with the IDs and value types of page items (u16 count, then records, see attributes.md). Evidence: the 1,252 trustworthy pairs of the corpus after 2026-10, 5,560 INDD object styles, 5,466 of them matched by name to an IDML ObjectStyle. Every style of DOM 7.0 to 21.5 has the same 360 IDs as its root style. InDesign 4.0 documents have 17 IDs in another layout; the converter writes no transparency for their styles.

Write rule. IDML writes an attribute of a style when the style's value differs from the value of the root style [None]. Counted over the matched styles, per style, setting and attribute (the drop shadow colour aside, below):

Category flag (chunk 0x1B92E)	Value differs from the root	Cells	In IDML
on	no	1,663,254	none
on	yes	371	all
off	no	3,480	none
off	yes	25	all

So the transparency categories (EnableTransparency="false") do not change what is written, and the comparison is with the root, not the style it is based on: 36 written values equal the parent's value, and 8 values equal to the root whose parent differs are not written. The root has the same list in all 1,252 documents and gets no setting element; neither does a style whose values all equal the root's. Opacity stops follow the same rule: the root has an empty list, and the 11 styles with stops have them in IDML (8 with the category on, 3 off), all matching the formula below. Their Self is u<style UID in hex><setting>1GradientFeatherSetting1OpacityGradientStop<i> (23 of 23 stops).

IDML writes the settings after FrameFittingOption and before ObjectStyleObjectEffectsCategorySettings in all 184 styles that have them. No style has ContentTransparencySetting.

Drop shadow colour. The root stores 0 (no swatch) for the object drop shadow's EffectColor (0x10837). 14 styles store Black (0xB), 10 of them with the drop shadow on and 4 off, and none has an EffectColor in IDML; 9 styles store another swatch, and IDML writes it in all 9. The converter leaves out Black where the root stores 0, as for page items. In the stroke and fill blocks the root stores Black, so the rule above already leaves it out. Other colours follow the rule: outer glow Color/Black where the root has Paper (2 values), satin Color/Paper where the root has Black (2).

Blocks. The list holds four blocks of 69 attributes, for TransparencySetting, StrokeTransparencySetting, FillTransparencySetting and ContentTransparencySetting, plus the gradient feather and drop shadow KnockedOut IDs listed above for page items. The attributes are in the same order in every block, and the root's values agree with TransparencyDefaultContainerObject of the IDML at all 205 numeric, boolean and point positions:

Block	IDs
Stroke	0x10891 to 0x108A0, 0x108A3 to 0x108D7
Fill	0x108D8 to 0x108E7, 0x108EA to 0x108FF, 0x1EB00 to 0x1EB1E
Content	0x1EB28 to 0x1EB37, 0x1EB3A to 0x1EB6E
Object	0x10816 to 0x1081C, 0x1081E to 0x10822, 0x10825, 0x10837, 0x1084A, 0x1084D to 0x1087F

The object block's drop shadow Noise and UseGlobalLight and its feather Noise have no identified ID.

The converter writes on styles the page item IDs above and the IDs below, each shown by a value: in every style where IDML writes the attribute, the ID holds the IDML value (0 mismatches), at the position the block layout gives it. Values are as for page items: f64 with all digits, percent stored as percent, u16 1 true, blend modes by the code table below, colours as swatch UIDs.

Setting	Effect	Attribute: ID (values written)
Object	FeatherSetting	Mode: 0x10821, i32: 0 None, 3 Standard (2)
Object	InnerShadowSetting	Opacity: 0x10850 (1)
Object	BevelAndEmbossSetting	ShadowColor: 0x10875 (3)
Stroke	BlendingSetting	BlendMode: 0x10892 (2)
Stroke	OuterGlowSetting	Applied 0x108AF, Opacity 0x108B1, EffectColor 0x108B3, Spread 0x108B5 (2 each)
Fill	BlendingSetting	BlendMode: 0x108D9 (1)
Fill	DropShadowSetting	Mode 0x108DC (0 None, 1 Drop), XOffset 0x108DD, YOffset 0x108DE, UseGlobalLight 0x108E5 (2 each)
Fill	InnerShadowSetting	Applied 0x108EC, EffectColor 0x108ED, Opacity 0x108EF, Angle 0x108F0, Distance 0x108F1, ChokeAmount 0x108F3, Size 0x108F4 (2 each)
Fill	OuterGlowSetting	Applied 0x108F6, BlendMode 0x108F7, EffectColor 0x108FA, Size 0x108FD (2 each)
Fill	InnerGlowSetting	Applied 0x108FE (8), BlendMode 0x108FF (2), Opacity 0x1EB00 (8), EffectColor 0x1EB02 (2), Size 0x1EB05 (8)
Fill	BevelAndEmbossSetting	Applied 0x1EB07, Size 0x1EB0C, Soften 0x1EB0D, Angle 0x1EB0E, Altitude 0x1EB0F, HighlightOpacity 0x1EB13, ShadowOpacity 0x1EB16 (2 each)
Fill	SatinSetting	Applied 0x1EB17, EffectColor 0x1EB18, BlendMode 0x1EB19, Opacity 0x1EB1A, Angle 0x1EB1B, Distance 0x1EB1C, Size 0x1EB1D, InvertEffect 0x1EB1E (2 each)

Styles confirm page item rows as well, for example drop shadow Mode (32 values), XOffset and YOffset (29), Opacity and Size (25), EffectColor (9) and KnockedOut (121 values, all false, in 31 documents; the root stores 1), and the fill and stroke gradient feathers (Applied 7 and 1, Angle 6 and 1, stops 7 and 1).

With these rows the converter reproduces, over the 1,252 trustworthy pairs, 491 of the 493 transparency attribute values of object styles (stop attributes counted one by one), with no value that IDML does not have. The 2 left are HonorOtherEffects of a fill drop shadow, which has no identified ID. The IDs found on styles are written on styles only; no page item sample was checked against them.

Not converted

• Drop shadow Noise, and UseGlobalLight other than that of the fill drop shadow of object styles.
• On page items, the stroke, fill and content effects other than the gradient feather and fill opacity. One text frame has ContentTransparencySetting with an inner glow and a satin effect applied, and two attributes set to 1, so it cannot show which is which.
• On object styles, the attributes that no sample shows by a value (unknowns.md), and ContentTransparencySetting.
• GradientFeatherSetting/Type: Linear in every sample.
• Transparency of placed graphics.