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. 7 guides, 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 full recipes 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 guides

1. 01blend, 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
2. 02blend 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
3. 03making 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
4. 04fading one photo into anotherDesigns a controlled crossfade: alignment first, then matched exposure, then the width of the transition.SettlesWhy a fade looks like a seam, and which of the three to fix.About 4 minutes
5. 05srgb or linear lightWhy the same blend mode gives different numbers when values are converted to linear light first — and how to choose either in the blender.SettlesWhy another editor's blend may not match this one.About 4 minutes
6. 06how the output size is worked outThe sum on the rulers — margin, picture, gap, picture, margin — and why an exact width can be solved in one step rather than searched for.SettlesWhy the file is exactly the width you typed, and when it cannot be.About 5 minutes
7. 07photo and signature for exam formsSourced sizes from published notices, which forms want one file and which want two, and how a KB range is hit without wrecking the picture.SettlesWhether to merge at all, and what size to save each part.About 6 minutes

What is not written down, and why

There is no page here about laying a cut-out subject on a backdrop: that is a placement job with different controls and different failure modes, and an essay about it on this site would be an essay about software this site does not contain. Arranging whole pictures side by side, stacked or in a grid is what the board on the front page does, and it prints its own arithmetic on its rulers as you work.

Nor is there a changelog, a roadmap or a tutorial series. A few 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.