Live histogram overlay
Toggleable 256-bin luminance histogram on the viewfinder.
Where to find it
Viewfinder Histogram toolbar button
Summary
Toggle a 256-bin luminance histogram over the live preview. The histogram is computed from the Y plane of every preview frame, normalized for display, and updates in real time. When you log a shot the histogram is frozen so the saved card matches what you saw at the moment of capture.
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How it works
What it does
Tap the histogram button in the viewfinder toolbar to overlay a luminance histogram on the live preview. The horizontal axis is brightness from black on the left to white on the right; the vertical axis is how many pixels in the current frame sit at that brightness. The overlay updates several times a second as you move the camera.
How it is computed
The app reads the Y (luminance) plane of every preview frame, bins each pixel into one of 256 brightness buckets, and normalizes the bin counts to 0.0 to 1.0 for display. This is the same data the protect chips and the auto-zones detector pull from, so the histogram is always consistent with the meter.
Reading the histogram
A bell-shaped curve in the middle is a balanced exposure. A spike at the right edge means highlights are clipping. A spike at the left edge means shadows are crushed. A bimodal curve (two humps) is normal for high-contrast scenes like sun and shade.
Frozen on log
When you log a shot the current histogram is captured into the shot's card (feature 4.6), even if the toggle is off. So the card always carries the histogram for the metered frame, regardless of whether you had the live overlay on at the time.
Persistence
The on/off state saves to your profile and survives a full app close. If you turn the histogram on and reopen the app later, the overlay comes back on automatically.