Add image adjustment sliders, mask alpha, Load Prev Mask, and button state colours

- Three vertical sliders (Brightness, Contrast, Gamma) to the left of the
  canvas for display-only image adjustment; all use power/linear formulae
  applied on-the-fly without touching saved data
- Alpha slider controls mask overlay transparency
- Brush size slider moved to its own row
- Each slider has a reset (↺) button restoring its default value
- Hide Mask button turns red when active; Eraser button turns orange
- Load Prev Mask button copies the saved mask from the previous clip in
  the list onto the current clip; the action is pushed onto the undo stack
  so it can be reverted with Undo
- Right survey panel narrowed (stretch factor 2 → 1)
- README Controls section updated to document all new features

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -124,17 +124,38 @@ Copy `config/clips.example.txt` as a starting point.
 
 The window shows the video on the left (auto-playing) and the survey panel on the right.
 
+### Mask drawing
+
 | Action | How |
 |---|---|
 | Draw water mask | Click and drag on the video |
-| Erase mask | Toggle **Eraser** button, then drag |
+| Erase mask | Toggle **Eraser** button (turns orange when active), then drag |
 | Brush preview | A white circle follows the cursor showing the current brush size |
+| Adjust brush size | **Brush size** slider below the controls; click **↺** to reset |
 | Undo last stroke | **Undo** |
 | Undo 10 strokes | **Undo×10** |
 | Redo | **Redo** — steps forward through undone strokes |
 | Clear entire mask | **Clear** |
-| Adjust brush size | Slider next to the erase controls |
+| Toggle mask overlay | **Hide Mask / Show Mask** — button turns red when hidden; does not affect mask data |
-| Toggle mask overlay | **Hide Mask / Show Mask** — hides or reveals the green overlay without affecting the mask data |
+| Mask transparency | **Alpha** slider below the controls; click **↺** to reset |
+| Load mask from previous clip | **Load Prev Mask** — copies the saved mask of the previous clip in the list onto the current clip; the action is undoable with **Undo** |
+
+### Image display adjustments
+
+Three vertical sliders sit to the left of the video and affect display only — they do not change what is saved.
+
+| Slider | Effect | Range |
+|---|---|---|
+| Brightness | Shifts all pixel values up or down | −100 to +100 |
+| Contrast | Scales pixel values around the midpoint | −100 to +100 |
+| Gamma | Applies a power-law correction (higher = brighter) | 0.1× to 3.0× |
+
+Click **↺** below any slider to restore its default value.
+
+### Navigation
+
+| Action | How |
+|---|---|
 | Save and continue | **Next** — saves current clip and loads the next one. If the clip already has a saved annotation a dialog asks whether to replace it or keep the existing save. |
 | Go back | **Previous** — saves current clip and returns to the previously viewed clip. Disabled on the first clip. |
 | Skip without saving | **Skip** — discards any unsaved changes and loads the next clip without writing anything to disk. |

src/river_annotation_tool/annotator.py

@@ -4,7 +4,7 @@ from pathlib import Path
 import cv2
 import numpy as np
 from PIL import Image
-from PySide6.QtCore import QTimer
+from PySide6.QtCore import Qt, QTimer
 from PySide6.QtWidgets import (
     QApplication,
     QButtonGroup,
@@ -113,9 +113,10 @@ class Annotator(QMainWindow):
         btn_undo = QPushButton("Undo")
         btn_undo10 = QPushButton("Undo×10")
         btn_redo = QPushButton("Redo")
+        btn_load_prev_mask = QPushButton("Load Prev Mask")
 
         row1 = QHBoxLayout()
-        for b in [self.btn_prev, btn_next, btn_skip]:
+        for b in [self.btn_prev, btn_next, btn_skip, btn_load_prev_mask]:
             row1.addWidget(b)
 
         row2 = QHBoxLayout()
@@ -128,13 +129,42 @@ class Annotator(QMainWindow):
             self.mc.btn_mask,
         ]:
             row2.addWidget(b)
-        row2.addWidget(QLabel("Brush"))
+
-        row2.addWidget(self.mc.brush_slider)
+        row3 = QHBoxLayout()
+        row3.addWidget(QLabel("Brush size"))
+        row3.addWidget(self.mc.brush_slider)
+        row3.addWidget(self.mc.brush_reset)
+
+        row4 = QHBoxLayout()
+        row4.addWidget(QLabel("Alpha"))
+        row4.addWidget(self.mc.alpha_slider)
+        row4.addWidget(self.mc.alpha_reset)
+
+        vert_panel = QHBoxLayout()
+        vert_panel.setContentsMargins(0, 0, 4, 0)
+        for label_text, slider, reset_btn in [
+            ("Brightness", self.mc.brightness_slider, self.mc.brightness_reset),
+            ("Contrast", self.mc.contrast_slider, self.mc.contrast_reset),
+            ("Gamma", self.mc.gamma_slider, self.mc.gamma_reset),
+        ]:
+            col = QVBoxLayout()
+            lbl = QLabel(label_text)
+            lbl.setAlignment(Qt.AlignmentFlag.AlignHCenter)
+            col.addWidget(lbl)
+            col.addWidget(slider, 1)
+            col.addWidget(reset_btn)
+            vert_panel.addLayout(col)
+
+        canvas_row = QHBoxLayout()
+        canvas_row.addLayout(vert_panel)
+        canvas_row.addWidget(self.mc.canvas, 1)
 
         left = QVBoxLayout()
-        left.addWidget(self.mc.canvas)
+        left.addLayout(canvas_row)
         left.addLayout(row1)
         left.addLayout(row2)
+        left.addLayout(row3)
+        left.addLayout(row4)
 
         left_widget = QWidget()
         left_widget.setLayout(left)
@@ -143,7 +173,7 @@ class Annotator(QMainWindow):
 
         main = QHBoxLayout()
         main.addWidget(left_widget, 3)
-        main.addWidget(right_widget, 2)
+        main.addWidget(right_widget, 1)
 
         container = QWidget()
         container.setLayout(main)
@@ -156,6 +186,7 @@ class Annotator(QMainWindow):
         btn_undo.clicked.connect(self.mc.undo)
         btn_undo10.clicked.connect(self.mc.undo10)
         btn_redo.clicked.connect(self.mc.redo)
+        btn_load_prev_mask.clicked.connect(self.load_prev_mask)
 
         if self._pending_answers:
             self._set_answers(self._pending_answers)
@@ -339,3 +370,28 @@ class Annotator(QMainWindow):
 
     def skip_clip(self):
         self._advance_clip()
+
+    def load_prev_mask(self):
+        try:
+            idx = self.selector.clips.index(self.filename)
+        except ValueError:
+            return
+        if idx == 0:
+            QMessageBox.information(
+                self, "No previous clip", "This is the first clip in the list."
+            )
+            return
+        prev_clip = self.selector.clips[idx - 1]
+        mask_path = self.out_dir / prev_clip.stem / self.cfg.filenames.mask
+        if not mask_path.exists():
+            QMessageBox.information(
+                self, "No mask found", f"No saved mask found for '{prev_clip.stem}'."
+            )
+            return
+        mask_full = np.array(Image.open(mask_path).convert("L"))
+        mask = cv2.resize(
+            (mask_full > 127).astype(np.uint8),
+            (self.dw, self.dh),
+            interpolation=cv2.INTER_NEAREST,
+        )
+        self.mc.set_mask(mask)

src/river_annotation_tool/mask_canvas.py

@@ -9,6 +9,12 @@ from PySide6.QtWidgets import QPushButton, QSlider
 class MaskCanvas:
     """Matplotlib canvas with brush-based mask drawing, undo/redo, and erase."""
 
+    _BRUSH_DEFAULT = 5
+    _ALPHA_DEFAULT = 40
+    _BRIGHTNESS_DEFAULT = 0
+    _CONTRAST_DEFAULT = 0
+    _GAMMA_DEFAULT = 100
+
     def __init__(self, frames, dh: int, dw: int):
         self.dh = dh
         self.dw = dw
@@ -19,6 +25,7 @@ class MaskCanvas:
         self.erase_mode = False
         self.drawing = False
         self.mask_visible = True
+        self._current_frame = frames[0]
 
         self._build_figure(frames)
         self._build_controls()
@@ -40,9 +47,36 @@ class MaskCanvas:
     def _build_controls(self):
         self.btn_erase = QPushButton("Eraser")
         self.btn_mask = QPushButton("Hide Mask")
+
         self.brush_slider = QSlider(Qt.Horizontal)
         self.brush_slider.setRange(2, 50)
-        self.brush_slider.setValue(5)
+        self.brush_slider.setValue(self._BRUSH_DEFAULT)
+        self.brush_reset = QPushButton("↺")
+        self.brush_reset.setFixedWidth(28)
+
+        self.alpha_slider = QSlider(Qt.Horizontal)
+        self.alpha_slider.setRange(0, 100)
+        self.alpha_slider.setValue(self._ALPHA_DEFAULT)
+        self.alpha_reset = QPushButton("↺")
+        self.alpha_reset.setFixedWidth(28)
+
+        self.brightness_slider = QSlider(Qt.Vertical)
+        self.brightness_slider.setRange(-100, 100)
+        self.brightness_slider.setValue(self._BRIGHTNESS_DEFAULT)
+        self.brightness_reset = QPushButton("↺")
+        self.brightness_reset.setFixedWidth(28)
+
+        self.contrast_slider = QSlider(Qt.Vertical)
+        self.contrast_slider.setRange(-100, 100)
+        self.contrast_slider.setValue(self._CONTRAST_DEFAULT)
+        self.contrast_reset = QPushButton("↺")
+        self.contrast_reset.setFixedWidth(28)
+
+        self.gamma_slider = QSlider(Qt.Vertical)
+        self.gamma_slider.setRange(10, 300)
+        self.gamma_slider.setValue(self._GAMMA_DEFAULT)
+        self.gamma_reset = QPushButton("↺")
+        self.gamma_reset.setFixedWidth(28)
 
     def _connect_events(self):
         self.canvas.mpl_connect("button_press_event", self._on_press)
@@ -51,6 +85,25 @@ class MaskCanvas:
         self.canvas.mpl_connect("axes_leave_event", self._on_axes_leave)
         self.btn_erase.clicked.connect(self.toggle_erase)
         self.btn_mask.clicked.connect(self.toggle_mask)
+        self.alpha_slider.valueChanged.connect(self.redraw)
+        self.brightness_slider.valueChanged.connect(self._refresh_frame)
+        self.contrast_slider.valueChanged.connect(self._refresh_frame)
+        self.gamma_slider.valueChanged.connect(self._refresh_frame)
+        self.brush_reset.clicked.connect(
+            lambda: self.brush_slider.setValue(self._BRUSH_DEFAULT)
+        )
+        self.alpha_reset.clicked.connect(
+            lambda: self.alpha_slider.setValue(self._ALPHA_DEFAULT)
+        )
+        self.brightness_reset.clicked.connect(
+            lambda: self.brightness_slider.setValue(self._BRIGHTNESS_DEFAULT)
+        )
+        self.contrast_reset.clicked.connect(
+            lambda: self.contrast_slider.setValue(self._CONTRAST_DEFAULT)
+        )
+        self.gamma_reset.clicked.connect(
+            lambda: self.gamma_slider.setValue(self._GAMMA_DEFAULT)
+        )
 
     # ── clip transition ────────────────────────────────────────────
     def load_clip(self, frames, dh: int, dw: int, mask=None, title: str = ""):
@@ -59,13 +112,31 @@ class MaskCanvas:
         self.mask = mask if mask is not None else np.zeros((dh, dw), dtype=np.uint8)
         self.history = []
         self.redo_stack = []
-        self.img_artist.set_data(frames[0])
+        self._current_frame = frames[0]
+        self.img_artist.set_data(self._apply_image_adjustments(frames[0]))
         self.set_title(title)
         self.redraw()
 
     # ── frame / title ──────────────────────────────────────────────
     def set_frame(self, frame):
-        self.img_artist.set_data(frame)
+        self._current_frame = frame
+        self.img_artist.set_data(self._apply_image_adjustments(frame))
+        self.canvas.draw_idle()
+
+    # ── image adjustments ──────────────────────────────────────────
+    def _apply_image_adjustments(self, frame):
+        img = frame.astype(np.float32)
+        img += self.brightness_slider.value()
+        c = self.contrast_slider.value() / 100.0
+        img = (1.0 + c) * (img - 128.0) + 128.0
+        np.clip(img, 0, 255, out=img)
+        g = self.gamma_slider.value() / 100.0
+        img = (img / 255.0) ** (1.0 / g) * 255.0
+        return np.clip(img, 0, 255).astype(np.uint8)
+
+    def _refresh_frame(self):
+        if self._current_frame is not None:
+            self.img_artist.set_data(self._apply_image_adjustments(self._current_frame))
             self.canvas.draw_idle()
 
     def set_title(self, text: str):
@@ -80,11 +151,19 @@ class MaskCanvas:
         self.redo_stack = []
         self.redraw()
 
+    def set_mask(self, mask):
+        """Replace the mask and push the previous state onto the undo stack."""
+        self.history.append(self.mask.copy())
+        self.redo_stack.clear()
+        self.mask = mask
+        self.redraw()
+
     def redraw(self):
         if self.mask_visible:
+            alpha = self.alpha_slider.value() / 100.0
             rgba = np.zeros((self.dh, self.dw, 4))
             rgba[..., 1] = self.mask * 0.7
-            rgba[..., 3] = self.mask * 0.4
+            rgba[..., 3] = self.mask * alpha
         else:
             rgba = np.zeros((self.dh, self.dw, 4))
         self.mask_artist.set_data(rgba)
@@ -116,11 +195,21 @@ class MaskCanvas:
 
     def toggle_erase(self):
         self.erase_mode = not self.erase_mode
-        self.btn_erase.setText("Eraser ON" if self.erase_mode else "Eraser")
+        if self.erase_mode:
+            self.btn_erase.setText("Eraser ON")
+            self.btn_erase.setStyleSheet("background-color: orange; color: black;")
+        else:
+            self.btn_erase.setText("Eraser")
+            self.btn_erase.setStyleSheet("")
 
     def toggle_mask(self):
         self.mask_visible = not self.mask_visible
-        self.btn_mask.setText("Show Mask" if not self.mask_visible else "Hide Mask")
+        if self.mask_visible:
+            self.btn_mask.setText("Hide Mask")
+            self.btn_mask.setStyleSheet("")
+        else:
+            self.btn_mask.setText("Show Mask")
+            self.btn_mask.setStyleSheet("background-color: red; color: white;")
         self.redraw()
 
     def stamp(self, x, y):