Developing the shootis the slow part.
Kelvin reads a photograph — the scene, the light, what has technically gone wrong — and builds four complete edits from what it finds. Pick the one closest to what you had in mind and carry it across the rest of the folder.
It all runs on your Mac. There is no account and nothing is uploaded.
1.5 GB, model included · macOS 14+ · Apple Silicon · free, AGPL-3.0-only
Close to what the meter gave you, cleaned up.
Where the numbers actually come from
“Sunlight from the front creates a strong golden-hour glow with high contrast.”
That is the entire output: a few categories and a sentence of description, from a small vision model looking at a 768-pixel copy of the photograph. There are no numbers in it anywhere.
- Temp
- 7,740 K
- Tint
- +2
- Exposure
- 0.00 EV
- Contrast
- +10
- Highlight recovery
- −1
- Whites
- +16
- Blacks
- −7
These come from ordinary code reading the histogram and the EXIF. Run it twice on the same file and you get the same numbers — they are arithmetic, not a guess, and arithmetic can be checked.
Ask a two-billion-parameter model for an exposure and it will give you one — exposure: +0.37, delivered with the same confidence whether it is right or wrong, and afterwards no way to tell which it was. So Kelvin never asks the model for a number. It asks what a vision model can genuinely answer — backlit portrait, or landscape at dusk — and the exposure is then calculated from the histogram, the way any other photo software would calculate it.
The same rule holds for what is wrong with a photograph. Kelvin does not take the model’s word that the shadows are crushed or the sky is blown; it measures the histogram and finds out. When those two were checked against each other over seventy-seven real edits, they were not describing the same photographs — so the engine stopped asking. Fewer photographs come out worse than if it had done nothing at all.
The four candidates are survivors, not the whole field. The engine renders more styles than it shows, scores each against its own craft checks, and drops any with a real defect — a Dramatic that crushes a backlit frame into silhouette never reaches the menu.
Big enough to actually choose between
A professional can read +18 contrast off a list and picture the result. Everyone else needs to see it. So press C and the candidates take over the window — two side by side, or all four when you want the survey.
Two up is the default, because a comparison is a question, and this one or that one is a question anybody can answer. Zoom and pan apply to every tile at once, so you are never comparing two different parts of the frame, and what you are looking at is a real render rather than an enlarged thumbnail — a comparison of anything other than what you would actually get is worse than no comparison.
It finds the subject on its own
Kelvin picks out the subject and edits only that, leaving the rest of the frame alone. Invert the mask and the edit swaps sides: the background changes and the subject stays exactly as it was. A mask can be narrowed by colour or by light.
Detection finds whatever stands out most and then stops — it finds the car above, not the one tree behind it you wanted darker. So you can point at the thing you want instead, and the selection spreads from there until the picture stops matching. What gets stored is that point and a tolerance, never a bitmap, so the selection you approve on screen is the one that reaches a full-size export.
Where the thing you pointed at touches something else the same colour, the selection walks straight into it. Kelvin says so when that happens, and the brush is the way out: it adds and erases, so the spill comes back off by hand.
None of this is generative. There is no inpainting, no object removal and no sky replacement, and none of it is planned. Kelvin changes how a frame is developed, not what was in front of the lens.
The one exception is small and worth stating plainly: click a speck of sensor dust and Kelvin patches it, choosing a clean piece of the same photograph to cover it with. Nothing is invented and nothing is fetched — it is a few pixels moved a short distance, stored as a position rather than as pixels, so one click travels to the rest of the shoot and to the full-size export.
Applying it to the rest of the folder
Settle on a look for one frame and batch apply carries it across the others. The filmstrip groups the folder into the days the photographs were taken, counts the frames in each, and filters to keepers, undecided or edited when you want to work through one slice at a time.
It also flags problems before you go hunting for them. A frame with a strong colour cast says so, with a Fix button next to the warning.
Watch it work
Silent · 29 seconds · 1432×880
It works with the Wi-Fi off
A released build carries the model inside it, so the reading happens on your Mac and there is no upload step to wait for. If your library lives in iCloud it still lives in iCloud — Kelvin changes nothing about that, in either direction.
No account, no upload, no telemetry
There is no crash reporting either, and nothing to opt out of.
No server on the other end
The model ships inside the app rather than behind an API, so reading a photograph needs no network — there is nothing to wait for and nothing to go down.
Your originals are never written to
Edits are saved alongside as small JSON files. The RAW your camera wrote is left byte for byte as it was.
Exports keep your metadata, including location
It is on by default, because quietly deleting something you might need later is the worse mistake. One switch in the export options removes it.
- Opens
- RAW · JPEG · HEIC · PNG · TIFF
- Exports
- JPEG · HEIC · PNG · 16-bit TIFF
- Colour spaces
- sRGB · Display P3 · Adobe RGB
- Export size
- Full, or a long edge you choose
- Tests
- 783 — 562 core, 221 app
- CI
- Runs on every pull request
- Licence
- AGPL-3.0-only, with a CLA
- Requires
- macOS 14 or later · Apple Silicon
Shipped. Not finished.
Kelvin 0.8.2is real, and it is early. Everything above is the app running on real photographs from a Sony A7R IV, not a mockup — download it, point it at a folder, and check this page against what happens. A leading zero is an honest number: there will be rough edges, and the repository’s issue tracker is where they get fixed.
The source is public under AGPL-3.0-only — the repository is on GitHub, tests and licence and all. New releases land here and in the app’s own update check, which is on by default while Kelvin is this young — two switches in Settings turn it off, and the privacy page says exactly what it sends.
Kelvin-0.8.2.dmg · 1.5 GB, because the model ships inside the app · macOS 14+ · Apple Silicon