Title Overlay Rules

Steering rules for placing overlaid slide titles on illustrated slides. Covers the generation-time directive pattern, the zones in use, and the safety net that applies regardless of placement.

1. Engineer Negative Space at Generation Time

When a slide will have a title overlaid on an illustration, bake a TITLE SAFE ZONE directive into the image prompt before generation. Do not rely on post-hoc placement heuristics to find a safe zone — if the generator doesn't know about it, the subject will occupy the best area by default.

Directive to append to every Image prompt:

TITLE SAFE ZONE -- CRITICAL COMPOSITION RULE: Reserve the {zone} of
the 16:9 frame as clean uninterrupted negative space filled only with
{surface}. No subjects, objects, text, props, or focal points may
appear in this region. The scene's subjects must be composed entirely
in the remaining portion of the frame. This negative space will carry
an overlaid title.

Where {zone} is upper third, middle third, lower third, left half, or right half (see §2 for the full list), and {surface} is a short style-specific description of what should fill the zone (a uniform area drawn from the style anchor — for example, "an unbroken area of the painted sky", "a clean stretch of the studio backdrop", "a flat region of the base texture used elsewhere in the frame"). Always phrase the surface in the style's own vocabulary so the generator reaches for materials it already knows how to render.

2. Five Zones Cover Practical Compositions

Three horizontal-band zones and two half-frame zones are supported:

• upper_third — uniform backdrop above the subject (sky, ceiling, wall, gradient, etc. depending on style). Use for landscapes, portraits, hero shots, and most open compositions.
• middle_third — reserved center band, with the subject framing around it. Use for styles that produce TV sets, portrait frames, vignettes, windows, or any composition where the focal subject surrounds a clean central opening intended to hold the title.
• lower_third — uniform region below the subject. Use when the subject is centered and top-heavy (e.g. a poster, hero object, or sign that naturally leaves surface below it).
• left_half — left side of the frame reserved as clean surface, subject composed on the right. Use for split-panel, side-by-side, or "subject pushed to one side" compositions.
• right_half — mirror of left_half: subject on the left, clean surface on the right. Useful when the subject naturally faces or moves leftward.

Do not use left_third or right_third — a third of a 16:9 frame is too narrow a vertical column for readable horizontal title text. left_half / right_half give the title enough column width to wrap across a few lines.

3. Pick the Zone Per Slide Based on Subject Geometry

A global default fails. Assign the zone per slide based on where the subject naturally sits, in the vocabulary of the chosen style:

The concrete surface (sky, fabric, paper, parchment, gradient, etc.) is chosen from the deck's style anchor. The zone assignment is what this rule governs.

Persist assignments in the design brief as a per-slide table so the brief stays the single source of truth.

4. Brightness Is Not the Same as Cleanness

A brightness-based band picker conflates darkness with safe. A bright uniform backdrop is a valid title region; a dark cluttered scene is not. If you need a programmatic signal, use variance (low variance = uniform) rather than mean luminance. Better: specify the zone in the brief and skip the picker entirely.

5. Always Apply a Scrim Behind the Title

Regardless of zone choice, add a semi-transparent rectangle sized to the title zone (not the whole slide) between the background picture and the text. Scope matters: a full-slide scrim flattens the whole illustration, while a zone-sized scrim lifts the title locally and leaves the rest of the scene at full brightness.

Default: 45% black.

<p:sp>
  <p:spPr>
    <a:xfrm>.. zone box ..</a:xfrm>
    <a:prstGeom prst="rect"><a:avLst/></a:prstGeom>
    <a:solidFill>
      <a:srgbClr val="000000"><a:alpha val="45000"/></a:srgbClr>
    </a:solidFill>
    <a:ln><a:noFill/></a:ln>
  </p:spPr>
</p:sp>

OOXML child order inside <p:spPr> must be xfrm → prstGeom → solidFill → ln. Keynote (and some strict OOXML readers) silently drop the fill when <a:ln> precedes <a:solidFill>, which is the exact failure mode that makes "scrim isn't rendering" bugs look like "scrim has no visible effect."

Tinted scrims for styled decks

Pure black is the right default for neutral styles. Warm-toned decks (sepia, painted Western, golden hour) and cool-toned decks (cyanotype, night, deep space) read better with a scrim color sampled from the deck's own natural shadows — the title still sits on a darker field, but the darkening looks like "deeper shadow of the same style" rather than a black film dropped on top.

Suggested sampler (skills/presentation-creator/scripts/suggest-scrim-color.py):

1. Resize each illustration to ~200px longest edge.
2. Take the darkest 5% of pixels across the whole deck by Rec. 709 luminance.
3. Average their sRGB.
4. Clamp the result to a target luminance (~0.10) so mid-shadow averages don't produce a washed-out scrim.
5. Bump alpha above 45% slightly when the sample is chromatic (a tinted scrim loses some darkening power to the tint).

Persist the chosen color and alpha in the deck's design brief once, not per slide.

6. Callbacks and Bookends Break Under Independent Regen

When two slides are meant to be the same scene with one detail changed (bookend pattern — first and last slide of a deck), independent Gemini calls produce two different scenes. Generate the base slide first, then edit the callback slide from the base output instead of regenerating. This is consistent with the edit-vs-regenerate rule in illustration-rules.md: the callback is a content modification of an existing image, not a fresh concept.

7. Loop B Is the Recovery Pattern, Not the Primary Pipeline

When the up-front SAFE ZONE directive fails on a slide (the generator put the subject in the declared safe zone anyway):

1. Send the generated image + the original prompt + the title to a vision LLM, asking for a diagnosis and a revised prompt.
2. Regenerate with the revised prompt.

This costs an extra round-trip per slide. Use it only for the 10–25% of slides that resist the initial directive, not as the default path.