Reference

What is written down here

The four surfaces on this site turn a picture. These pages explain the thing the surfaces are working against, which is a single number in a metadata block and the long history of programs choosing whether to believe it. Neither page is a tutorial for a button. They are here because the commonest question about a sideways photograph — why does it look right in one place and wrong in another — has an answer that fits in a few hundred words, and nobody should have to reverse-engineer it from a tool’s output.

• Why a photo turns sideways when you upload it

  Where the disagreement starts: a sensor bolted to a body that turns, a field written instead of a rotation performed, and two programs reading the same bytes to opposite conclusions.

  Reading time about four minutes

• The eight orientation values, one by one

  A drawn glyph for every legal value showing how the samples really sit inside the file, why four of the eight include a reflection, and which two a camera will ever hand you.

  Reading time about six minutes

What is deliberately not written here

There is no page about choosing a crop ratio, about mirroring a picture for a transfer, about shrinking a file, or about any sequence of edits on one canvas. Those are different operations with different failure modes, and a reference page that drifted into them would be a reference page written to catch traffic rather than to answer a question. The same discipline governs the tools: the operation this site performs is a turn, and the metadata field that describes one.

Two subjects are named in the essays and deliberately left unfinished. The block transform that would turn a JPEG by ninety degrees without decoding it is described as a mechanism and is not shipped in this build, so nothing here may claim a lossless quarter turn. Frame-by-frame rotation of an animated file is the same case — the timing and disposal rules are the hard part, they are not implemented, and an animation saved from these tools comes back as one still frame.

Where to go after reading

If the second essay told you which value your file carries, the orientation surface is where that reading turns into a repair, and it will print the same value back to you before offering anything. If the problem is a whole folder of scans that all carry the same defect, the batch queue applies the reasoning to every file and accounts for each one. And if the picture is simply crooked rather than mis-tagged, that is a different job entirely and costs a crop, which the essays do not cover because it is geometry rather than metadata.