---
id: chart-image-adjustment
title: Chart Image Adjustment
category: Charts
---

![Fig 1. The Image Adjustment palette, opened from the tune icon in the chart list](chart-image-adjustment-1.jpg)

Aerial and satellite chart imagery is usually exposed for the land, which
can leave the water — where the hazards are — looking crushed and nearly
black. Adjusting the brightness and contrast can pull submerged rocks,
shallows, and reefs back into view, which is handy when you're scouting an
anchorage.

**To adjust a chart's image**, open the chart list and tap the **tune**
icon next to a chart (it appears alongside the existing opacity control,
for image-based charts only). The chart list closes and a compact **Image
Adjustment** palette opens over the map, headed by the name of the chart
layer you're working on.

The palette is modeless — there is no backdrop, so panning and zooming stay
available while you adjust. Drag it by its header to move it clear of the
water you're studying; it reopens wherever you last left it, even after a
reload.

**Brightness** and **Contrast** run from 0% to 200%, with 100% being
neutral, and the chart updates live as you drag. **RESET** returns both to
neutral. **SAVE** keeps your changes; closing the palette with its **close**
button instead discards them and puts the chart back as it was.

A saved adjustment is stored with that chart, alongside its opacity, so it's
still applied the next time you open Freeboard. Left untouched, a chart looks
exactly as it always has — the neutral default makes no visible change.

This applies to raster, tile, WMS, and WMTS image charts. Vector charts
(like S-57) don't have an image to adjust, so the control doesn't appear
for them.
