Test sheet: the correction curve target

What it prints

A 21-step wedge: twenty-one flat patches running from the lightest tone your process can hold to the darkest, printed as a negative on transparency film like everything else.

The patches are flat blocks, printed fit-to-page, because resolution genuinely cannot matter here — there's no detail to resolve. It's a measurement, not a picture.

The loop

• Print the target onto film.
• Expose and process it exactly as you would a real print. This is the important part: the curve you get describes whatever you actually did, so do the normal thing, not a careful special version of it.
• Scan or photograph the dry print and hand the image back to the wizard.
• It reads each patch and builds a curve from the difference between what was asked for and what appeared.

The wizard saves as it goes, so you can stop after the printing — which might be days before the scanning — and pick it up where you left off.

What the read-back tells you

The wizard plots your process's response and says plainly what it found. It will tell you when a print is unusable rather than building a curve from it, which is the more valuable answer: a curve measured from a bad print is worse than no curve, because it looks like knowledge.

Typical faults it names: patches that all read the same at one end (blocked shadows or blown highlights, so there's nothing to measure), and a print too flat overall to be informative.

Colour first, then the curve

A measured curve describes the whole chain that produced it: your printer, your film, your paper, your chemistry, your light — and the scale colour that was selected when you printed the target.

Change the colour afterwards and the curve is describing something you're no longer doing. So settle the colour first with the Basic or Advanced sheet, then measure the curve. Otherwise you'll measure twice.

Curves you build are yours: they're named what you name them, and they stay put when you change the app's language.

How to read any of these sheets

All four work the same way, and none of them can be judged on screen:

• Print the sheet onto transparency film, exactly as you print a negative — same printer, same film, same settings.
• Contact print it onto your sensitized paper, with your own light source and your own exposure.
• Process it as usual, dry it, and read the answer off the paper.

The blank bottom row is clear film. No ink at all. It exposes fully and prints your darkest tone, so it's the reference every column above it is read against.

Column headings are printed in clear, on a darkened band. Clear is the only "ink" guaranteed to print dark, so the labels stay readable on the finished print rather than disappearing.

Judge it dry, not wet.