reference
A label under a control can say what the control is called. It cannot say why the same number produces a clean result on one pair of photographs and grey sludge on the next, because that answer is arithmetic, and arithmetic does not fit in a tooltip.
So it lives here instead. Three pages, each written for one question that kept coming back, and each ending in something you can act on rather than something you can nod at. They are ordered the way they are useful: first whether per-pixel mixing is the operation you actually want, then which of the twelve functions to pick, then one full recipe assembled from both of those.
None of them is a tour of the interface. The instrument explains itself as you move it, and a page that narrated every slider would be a manual for software that does not need one. What is written down is the part the software cannot show you: the identity values, the asymmetries, the reason a mode clips where it does, and the order to reach for controls in when a blend has gone wrong.
The three pages
- blend, or placeSorts three operations that one English sentence keeps confusing, using the position of the second picture's edges as the only evidence.SettlesWhether this site is the right one for what you are holding.About 5 minutes
- blend modes by what they doGroups the twelve by their identity value — white, black or middle grey — and prints the line of arithmetic that predicts how each one clips.SettlesWhich mode to reach for, and why the wrong one goes muddy.About 11 minutes
- making a double exposureFollows one recipe from the choice of subject to the export, including the two controls that decide whether a face survives the texture laid over it.SettlesWhat to turn down when the branches have eaten the portrait.About 9 minutes
What is not written down, and why
There is no page here about laying a cut-out subject on a backdrop, none about tiling photographs into a grid, and none about stitching two screenshots end to end. Those are different operations with different controls and different failure modes, and an essay about them on this site would be an essay about software this site does not contain. The scope test in the first page above is the whole of what can honestly be said about them from here.
Nor is there a changelog, a roadmap or a tutorial series. Three pages that stay correct are worth more than thirty that drift, and every one of these will be rewritten rather than supplemented when the engine underneath it changes.