Reference
Reference pages on mirroring
Six pages, each written because one specific misunderstanding about reflection costs people an afternoon.
None of these teaches the controls. The bench has six modes and they explain themselves in use. What the bench cannot do while you are standing at it is settle the question that sent you to it — whether the picture in front of you was mirrored or turned, whether the press on the other end of the file will reverse it again, whether the face you are looking at is the one the sensor actually recorded. Each page takes one of those, follows it as far as the arithmetic or the hardware allows, and stops at the point where it would have to start guessing.
The six of them
- Mirrored or turned5 min
The determinant test, stated plainly: why a double reflection lands on exactly the grid a half turn lands on, and why no composition of flips will ever produce a quarter turn.
- Printing a mirrored image6 min
Four transfer processes, sorted by whether the press reverses the artwork for you, plus the one print-dialogue setting that silently undoes the reflection you just saved.
- Why your selfie is reversed4 min
The front camera shows a live mirror and writes the unmirrored frame to storage, which is why the face you approved is not the face anybody else has been looking at.
- Mirror and water images5 min
The two rules, the letters that survive each reflection, and worked examples with words and clocks of the kind reasoning papers set.
- Lossless JPEG flips6 min
Why a JPEG can be flipped by moving its 8 × 8 blocks without decoding it, the strip at the edge that cannot move, and the three ways a flipped JPEG gets written.
- Which transfers need mirroring4 min
Twelve print and transfer processes with a verdict, the reason, and the manufacturer or supplier page each one was checked against.
The gaps
What is not written up
A page gets written here when it can be checked against something the tool actually does. Reflecting an animation frame by frame is not built yet, so it has no reference page; it is named as a limit on the tool pages, because a limit you can read is worth more than a page that describes a feature the site does not have.
Turning is discussed in the first page. The workspace turns a picture in quarter steps alongside the reflection — the eight orientations a rectangle can take — because those are the turns that combine exactly with a mirror: nothing is resampled. Turning by an arbitrary angle is a different job with different costs, and it is not offered here.