PowerPoint · Colour
PowerPoint is my answer key now
With LibreOffice out of the picture I need a new reference. PowerPoint's own PDF export states almost everything it does, if you read it closely.
Matching LibreOffice was a good first test. It isn't the goal. The goal is to look like PowerPoint, and LibreOffice doesn't.
So this week the reference changed. I built a test deck covering what real decks use (fills, gradients, patterns, lines, arrowheads, preset shapes, tables, effects) and exported it to PDF from PowerPoint. That PDF is now the answer key.
A PDF is a much better witness than a screenshot. It doesn't just show pixels, it states the geometry: exact coordinates, exact colours, exact tile sizes. You just have to read it.
Pattern fills were twice as dense
PowerPoint has those old hatching patterns: diagonal lines, dots, grids. Mine looked roughly right, but next to PowerPoint's they looked coarse.
The PDF says why. PowerPoint writes a pattern as a 16×16 pixel tile repeated every 6 pt. I had taken the tile for the pattern. But the tile is really 2×2 copies of an 8×8 cell, so the actual repeat is 3 pt. Every pattern I drew was half as dense as it should be.
And the dot patterns aren't on a grid at all. They sit on a brick layout, every second row shifted by half. One dot per cell covers the same area but reads much coarser.
Shade and tint happen in linear light
Themes use colour tweaks everywhere: "accent 1, 50% darker". I had implemented that the obvious way, multiplying the RGB numbers by 0.5.
That's wrong, and not subtly. PowerPoint applies shade and tint in linear light, before the screen's gamma curve. Take the default blue #4472C4:
| Naive | PowerPoint | |
|---|---|---|
| 50% shade | #223962 | #2F528F |
| 40% tint | #B4C7E7 | #CFD5EA |
The naive version is visibly darker. Almost every theme uses shades and tints, so this one fix changes the colours of a huge number of slides at once.
Small things the PDF settled this week
- A line made of several strands (a "compound" line) has one end cap for the whole bundle, not one per strand.
- Stars and polygons fit the shape's box, not the ellipse inside it.
- A cube's faces are shaded by fixed amounts you can read straight off the PDF's colours.
- Arrowheads sit where PowerPoint puts them, which is not where you'd guess.
None of these is big on its own. But a slide is made of hundreds of these little decisions, and it only looks right when nearly all of them are right.
This is going to be the method from now on: find a place where Office states the truth, and measure against it.