Umbra

A notebook

In Umbra a point in the picture can be placed on a zone, so that it prints at the grey I choose.

Notes2
The Zones tool, sketched3
Place a tone on a zone4
Eleven zones, two pins5
Try it6
The Zones tool7
The wedge, close8
What each pin changes9
In short10

A RAW developer for the Mac, built for how I edit: cull from the keyboard, dodge and burn in layers, print in black and white.

1Umbra

Notes

There are eleven zones, one stop (a doubling of light) apart. Zone V is mid-grey, zone 0 is black and zone X is white.
Click a point and the tool reads the plain mean of a 5 by 5 pixel area around it.
Pick the zone the point should print in. Exposure moves by exactly the difference between the two zones.
In colour, a second point sets the contrast. There is no formula for it, so the tool halves the range fourteen times until it fits.
The contrast pivots on the first point, so the first point keeps its zone.
When no contrast setting reaches the zone, the wedge says so: “Zone X is out of reach.”
Each zone’s grey has a lightness (L*) of ten times its number: zone V is L* 50.
In black and white the second point sets Development instead, and Exposure moves to hold the first point’s density.
Esc undoes everything the tool changed since it opened, as one step. Return applies and closes.

2Notes

The Zones tool, sketched

Figure 1. The Zones tool, sketched in code: the picture cut into bands, a pin on one point, and the wedge, the row of eleven zones to pick from.

3Umbra

Chapter 1

Place a tone on a zone

In Umbra’s Zones tool I click a point in the picture and pick the zone it should print in. A zone is one of eleven grey bands, each one stop (a doubling of light) from the next. Exposure then moves by the number of stops between the zone the point is in and the one I picked.

In colour, a second point sets the contrast, and the first point keeps its zone. Exposure has an exact formula. Contrast has none, so the tool searches for it and says when no setting reaches the zone.

4Place a tone on a zone

Eleven zones, two pins

Zone	Stops from mid-grey	Print L*
0	-5	0
I	-4	10
II	-3	20
III	-2	30
IV	-1	40
V	+0	50
VI	+1	60
VII	+2	70
VIII	+3	80
IX	+4	90
X	+5	100

A point 1.7 stops under mid-grey sits in zone 3.3. Asked to print in zone V, it moves Exposure by exactly +1.7 EV (exposure value, counted in stops). A second point, 2.4 stops over, is asked to print in zone VIII. Fourteen halvings of the range find Contrast -67, with the pivot on the first point, which still prints at L* 49. Asked to print in zone X, a point near mid-grey is out of reach, and the wedge says so.

Table 1. The eleven zones, and the two pins worked through in the text. They were computed when the page was built, by the Zones tool’s method ported to this page. The page uses its own tone curve, so the method is the app’s and the numbers are the page’s.

5Umbra

Try it

show zones

Click the photograph to place a point.

Figure 2. The Zones tool’s method on one of my photographs, printed through the page’s own tone curve. A point reads the mean of the 5 by 5 pixels around it, as in the app. Click a point and pick its zone, then click a second point and pick again.

6Try it

The Zones tool

Umbra’s Develop window: the photograph drawn as flat grey bands, a round pin on a wall, and a small wedge of eleven grey swatches beside it reading NOW V.

Plate 1. The Zones tool on one of my photographs, in the colour tab. The picture is drawn as eleven grey bands, the pin sits in zone V, and picking another zone on the wedge moves Exposure by the difference.

7Umbra

The wedge, close

A close view of the wedge: eleven grey swatches from black to white, the sixth outlined, NOW V above it, and the pin just left of it.

Plate 2. The wedge, enlarged from the same frame. Each swatch is one zone, one stop apart, from black to white; the outlined one is the zone the pinned point is in.

8The wedge, close

What each pin changes

Figure 3. Top: the eleven zones in their own tones, with exposure carrying pin A up the wedge. Bottom: the zone a tone was against the zone it prints in. Contrast tilts that line about pin A, so pin B moves.

1Every point has a zone: its stops from mid-grey, plus five.
2Pin A: exposure moves it to the zone picked.
3Pin B: contrast moves it, pivoting on pin A. The tool finds the value by bisection: it halves the range fourteen times.

9Umbra

In short

Exposure is arithmetic and contrast is a search. The Zones tool is exact where it can be, and says “out of reach” where no setting fits.

The rest of Umbra is in the case study: culling from the keyboard, dodge and burn in layers, and the black and white print.

the case study

another notebook Operator

notebooks

10In short