Create a custom test chart

Calibration Flow doesn't have a screen where you pick your chart's dimensions or patch count. What exists: a control strip built into the negative, a mode for testing several curves on one print, and standalone chart generators on the site. This page says exactly what's adjustable in each, and what isn't adjustable anywhere.

#What exists today

The control strip, in the Negative screen. In the bottom options bar (Format · Style · Effects · Target), the "Show the target" toggle adds a 25-step grey scale to the bottom left of your negative — a 5×5 grid of patches plus a continuous gradient column. It's drawn before the negative inversion, so it carries exactly the same transform as your image (chosen curve and inversion included). With no curve selected, you get a raw target for a first calibration; with a curve, a control target, to check it holds on the print. Free, no Pro lock.

Multi-zone mode, to compare several curves. In the same Target tab, you can split the image into 1, 2 or 4 zones: each zone gets its own small control strip with its own curve, and a label carrying the name of that zone's curve, to tell them apart. That lets you test two or four settings on a single print instead of running as many separate ones.

#What doesn't exist

No custom dimensions, no chosen patch count, no dedicated screen where you'd set these parameters yourself. The control strip always follows your negative's format (Format tab) and resolution (Effects tab) — there's no standalone "chart only" file to download from the app.

#For a standalone chart to print: the site's generators

If you want a chart file independent of your negative — for a quick test strip, a check before you've even picked your image, or just a chart to keep on hand —, the site's free generators remain the best option, no account or install needed:

• The 21-step chart: 3×7 grid + gradient, your choice of positive or negative polarity, continuous tone, PNG 1680×668 px at 300 dpi, no watermark.
• The process pages (for instance cyanotype calibration) carry the same generator in 25 patches (5×5 + gradient) — the same computation as the app's control strip. On the screen printing calibration page, this generator comes out positive and lets you pick the rendering (continuous, halftone or diffusion) and, when screened, a fineness of 300, 450 or 600 dpi.
• The Color Venn, for CMYK colour printing, on the gum bichromate calibration and carbon calibration pages.

None of these generators offer a custom format or patch count either — each fixes its own composition. What they give you: a standalone chart file, independent of your image, that you can print before you've even picked your photo.

#Workarounds for a genuinely unusual format

For an out-of-the-ordinary need — a square print, an unusual format, a 5-patch strip only —, the remaining options are manual:

Photoshop as a generator. Download a chart from the site (21-step or 25-patch), open it in Photoshop, resize and crop to the format you want. Laborious, but it works for a one-off need.

Physical cropping after printing. Print the standard chart, then cut it to the final format. You lose a few patches if you cut too close, but for most reasonable formats, it's enough.

#Technical details

The control strip is drawn into the negative file itself: it follows its resolution and format, it isn't a separate setting. Turning on "Show the target" automatically disables "Fill the paper": the two don't go together.

#Key points

#In practice

For most uses, the negative's control strip is enough: it tells you whether your curve holds, with no extra step. If you need a standalone chart — to compare several papers, or before picking your image —, start with the site's generators: they handle most real needs. Save the Photoshop workaround for genuinely unusual cases.