Keep the LUT range in data units with the Z-axis log scale (color bar, contrast panel)

doc/release_notes/release_2.12.md

@@ -8,6 +8,7 @@
 
 🛠️ Bug fixes:
 
+* **Z-axis logarithmic scale** — With the Z-axis logarithmic scale enabled (`ZAxisLogTool`), the color bar, the contrast adjustment panel and the LUT range used logarithms of the image values instead of the image values themselves. The color bar now shows the original image values on a logarithmic scale, with the same colors as the image, consistently with the cursor values. In the contrast adjustment panel, the range now matches the histogram, so that the "Full range", "Eliminate %", "Min." and "Max." actions no longer show the image with a single color. Cross sections and exported images with the LUT applied now follow the logarithmic color mapping. Images with values lower than 1 (e.g. between 0 and 1) are no longer shown with a single color: values lower than or equal to zero are now shown with the lowest color of the colormap. Enabling the logarithmic scale sets the LUT range to the full range of the positive values, and disabling it restores the previous LUT range. The Z-axis log tool is now disabled for image items which do not support it (RGB images, 2D histograms, quadrilateral grids and image filters). API change: with the logarithmic scale, `get_lut_range`, `set_lut_range`, `get_lut_range_full` and the `lut_range` argument of `set_data` now use data units instead of base-10 logarithms, and the new `BaseImageItem.supports_zaxis_log` method tells whether an image item supports the logarithmic scale (closes [Issue #63](https://github.com/PlotPyStack/PlotPy/issues/63))
 * **Editing points of downsampled curves** — With downsampling enabled, moving a curve point modified another point of the curve data than the one shown, since the handle of a drawn point was used as an index into the full data
 * **Curve fitting dialog** — Running the automatic fit no longer raises `OverflowError: argument 1 overflowed` errors when a fitted value ends up far outside the range of its slider (e.g. with the Powell method on a fit range restricted to the tail of a peak). These errors left the slider of the parameter unresponsive, and the values of the following parameters were not displayed. Such values are now shown with a warning icon, whose tooltip gives the slider range, while the slider stays at its nearest end. Typing `nan` or `inf` in a parameter field now restores the previous value instead of raising errors, and the number of slider steps must be at least 2 in the parameter properties dialog (closes [Issue #76](https://github.com/PlotPyStack/PlotPy/issues/76))
 * **Cross-section panels with many hidden images** — X/Y cross-section panels kept one curve for every image ever displayed, even after it was hidden, so plots containing hundreds of hidden images became progressively slower to refresh. Curves are now only kept for visible images, and are recreated when a hidden image is shown again

plotpy/items/image/base.py

@@ -188,6 +188,9 @@ class BaseImageItem(QwtPlotItem):
     _readonly = False
     _private = False
     _icon_name = "image.png"
+    #: True if the item supports the Z-axis logarithmic scale, i.e. if it draws
+    #: its data through :meth:`_get_display_data` (see :meth:`supports_zaxis_log`)
+    _ZAXIS_LOG_SUPPORTED = False
 
     def __init__(
         self, data: np.ndarray | None = None, param: Any | None = None
@@ -211,6 +214,13 @@ def __init__(
 
         self.data: np.ndarray | None = None
 
+        # Z-axis logarithmic scale support: the LUT range (`min`, `max`) is always
+        # expressed in data units, only the color mapping is logarithmic
+        self._log_data: np.ndarray | None = None
+        self._log_floor = 1.0
+        self._lin_lut_range: tuple[float, float] | None = None
+        self._is_zaxis_log = False
+
         self.min = 0.0
         self.max = 1.0
         self.cmap_table = None
@@ -238,11 +248,6 @@ def __init__(
 
         self.histogram_cache = None
 
-        # Z-axis logarithmic scale support
-        self._log_data: np.ndarray | None = None
-        self._lin_lut_range: tuple[float, float] | None = None
-        self._is_zaxis_log = False
-
         if data is not None:
             self.set_data(data)
         self.param.update_item(self)
@@ -451,8 +456,47 @@ def _recompute_log_data(self) -> None:
         Used both when toggling the Z-axis log scale on and when the underlying
         data is replaced (e.g. via :meth:`set_data`) while the log scale is
         already active.
+
+        Values lower than or equal to zero have no logarithm: they are replaced
+        by the smallest positive value of the data (the "log floor", or 1.0 if
+        there is no positive value), so that they are shown with the lowest
+        color of the colormap. NaN values are kept.
+        """
+        data = np.asarray(self.data)
+        with np.errstate(invalid="ignore"):
+            positive = data[data > 0]
+        self._log_floor = float(positive.min()) if positive.size else 1.0
+        with np.errstate(invalid="ignore", divide="ignore"):
+            self._log_data = np.log10(
+                np.maximum(data, self._log_floor, dtype=np.float64)
+            )
+
+    def _get_display_data(self) -> np.ndarray:
+        """Return the data to which the LUT is applied when drawing the image
+
+        Returns:
+            Base-10 logarithm of the data if the Z-axis log scale is enabled,
+            the data itself otherwise
+        """
+        if self._is_zaxis_log:
+            return self._log_data
+        return self.data
+
+    def _to_lut_space(self, values: np.ndarray) -> np.ndarray:
+        """Convert data values to the space in which the LUT is applied
+
+        Args:
+            values: Data values
+
+        Returns:
+            Base-10 logarithm of the values (see :meth:`_recompute_log_data` for
+            values lower than or equal to zero) if the Z-axis log scale is enabled,
+            the values themselves otherwise
         """
-        self._log_data = np.array(np.log10(self.data.clip(1)), dtype=np.float64)
+        if self._is_zaxis_log:
+            with np.errstate(invalid="ignore", divide="ignore"):
+                return np.log10(np.maximum(values, self._log_floor, dtype=np.float64))
+        return values
 
     def set_data(
         self, data: np.ndarray, lut_range: tuple[float, float] | None = None
@@ -461,24 +505,27 @@ def set_data(
 
         Args:
             data: 2D NumPy array
-            lut_range: LUT range -- tuple (levelmin, levelmax) (Default value = None)
+            lut_range: LUT range -- tuple (levelmin, levelmax), in data units, even
+             when the Z-axis log scale is enabled (Default value = None)
         """
         self.data = data
         self.histogram_cache = None
         self.update_bounds()
         self.update_border()
         # Refresh the cached log10 data when log scale is active, otherwise the
         # display would keep using the previous (now stale) log data.
-        if self.get_zaxis_log_state():
+        if self._is_zaxis_log:
             self._recompute_log_data()
         if not self.param.keep_lut_range:
-            if lut_range is not None:
-                _min, _max = lut_range
-            elif self.get_zaxis_log_state():
-                _min, _max = get_nan_range(self._log_data)
-            else:
-                _min, _max = get_nan_range(data)
-            self.set_lut_range((_min, _max))
+            if self._is_zaxis_log:
+                # The linear LUT range, restored when the log scale is disabled,
+                # is updated as it would have been without the log scale
+                self._lin_lut_range = (
+                    get_nan_range(data) if lut_range is None else tuple(lut_range)
+                )
+            if lut_range is None:
+                lut_range = self.get_lut_range_full()
+            self.set_lut_range(lut_range)
 
     def get_data(
         self, x0: float, y0: float, x1: float | None = None, y1: float | None = None
@@ -598,7 +645,8 @@ def set_interpolation(self, interp_mode: int, size: int | None = None) -> None:
         if interp_mode in (INTERP_NEAREST, INTERP_LINEAR):
             self.interpolate = (interp_mode,)
         if interp_mode == INTERP_AA:
-            aa = np.ones((size, size), self.data.dtype)
+            # The kernel must have the same data type as the data drawn
+            aa = np.ones((size, size), self._get_display_data().dtype)
             self.interpolate = (interp_mode, aa)
 
     def get_interpolation(self) -> tuple[int] | tuple[int, np.ndarray]:
@@ -610,17 +658,29 @@ def set_lut_range(self, lut_range: tuple[float, float]) -> None:
         Set the current active lut range
 
         Args:
-            lut_range: Lut range, tuple(min, max)
+            lut_range: Lut range, tuple(min, max), in data units (even when the
+             Z-axis log scale is enabled: values lower than or equal to zero are
+             then replaced by the smallest positive value of the data)
 
         Example:
             >>> item.set_lut_range((0.0, 1.0))
         """
-        self.min, self.max = lut_range
+        vmin, vmax = lut_range
+        if self._is_zaxis_log:
+            if vmax <= 0:
+                vmax = self._log_floor
+            if vmin <= 0:
+                vmin = min(self._log_floor, vmax)
+        self.min, self.max = vmin, vmax
         _a, _b, bg, cmap = self.lut
-        if self.max == self.min:
-            self.lut = (LUT_MAX, self.min, bg, cmap)
+        if self._is_zaxis_log:
+            lmin, lmax = np.log10(float(vmin)), np.log10(float(vmax))
+        else:
+            lmin, lmax = self.min, self.max
+        if lmax == lmin:
+            self.lut = (LUT_MAX, lmin, bg, cmap)
         else:
-            fmin, fmax = float(self.min), float(self.max)  # avoid overflows
+            fmin, fmax = float(lmin), float(lmax)  # avoid overflows
             self.lut = (
                 LUT_MAX / (fmax - fmin),
                 -LUT_MAX * fmin / (fmax - fmin),
@@ -632,7 +692,7 @@ def get_lut_range(self) -> tuple[float, float]:
         """Get the current active lut range
 
         Returns:
-            tuple[float, float]: Lut range, tuple(min, max)
+            tuple[float, float]: Lut range, tuple(min, max), in data units
         """
         return self.min, self.max
 
@@ -648,35 +708,61 @@ def get_lut_range_full(self) -> tuple[float, float]:
         """Return full dynamic range
 
         Returns:
-            tuple[float, float]: Lut range, tuple(min, max)
+            tuple[float, float]: Lut range, tuple(min, max), in data units. When the
+            Z-axis log scale is enabled, the minimum is the smallest positive value
+            of the data.
         """
-        return get_nan_range(self.data)
+        vmin, vmax = get_nan_range(self.data)
+        if self._is_zaxis_log:
+            return self._log_floor, max(vmax, self._log_floor)
+        return vmin, vmax
 
     # ---- Z-axis logarithmic scale --------------------------------------------
+    def supports_zaxis_log(self) -> bool:
+        """Return True if the item supports the Z-axis logarithmic scale
+
+        Items which do not support it (e.g. RGB images, which have no colormap)
+        are ignored by :class:`.ZAxisLogTool`, and :meth:`set_zaxis_log_state`
+        has no effect on them.
+        """
+        return self._ZAXIS_LOG_SUPPORTED
+
     def get_zaxis_log_state(self) -> bool:
         """Return True if Z-axis is in logarithmic scale"""
         return self._is_zaxis_log
 
     def set_zaxis_log_state(self, state: bool) -> None:
         """Set Z-axis logarithmic scale state
 
+        With the logarithmic scale, the colors are mapped to the base-10 logarithm
+        of the data, whereas the LUT range (see :meth:`get_lut_range`), the color
+        bar, the contrast adjustment panel and the cursor values remain in data
+        units. Values lower than or equal to zero are shown with the lowest color
+        of the colormap.
+
+        Enabling the logarithmic scale sets the LUT range to the full range of the
+        positive values of the data; disabling it restores the previous LUT range.
+
         Args:
             state: True to enable logarithmic scale, False otherwise
         """
-        self._is_zaxis_log = state
-        plot = self.plot()
+        state = bool(state)
+        if not self.supports_zaxis_log() or state == self._is_zaxis_log:
+            return
         if state:
             self._lin_lut_range = self.get_lut_range()
-            if self._log_data is None:
+            self._is_zaxis_log = True
+            if self.data is not None:
                 self._recompute_log_data()
-            self.set_lut_range(get_nan_range(self._log_data))
-            dtype = self._log_data.dtype
+                self.set_lut_range(self.get_lut_range_full())
         else:
+            self._is_zaxis_log = False
             self._log_data = None
             self.set_lut_range(self._lin_lut_range)
-            dtype = self.data.dtype
-        if self.interpolate[0] == INTERP_AA:
+        if self.data is not None and self.interpolate[0] == INTERP_AA:
+            dtype = self._get_display_data().dtype
             self.interpolate = (INTERP_AA, self.interpolate[1].astype(dtype))
+        plot = self.plot()
         if plot is not None:
             plot.update_colormap_axis(self)
 
@@ -766,7 +852,12 @@ def draw_image(
         if self.warn_if_non_linear_scale(painter, canvasRect):
             return
         dest = _scale_rect(
-            self.data, src_rect, self._offscreen, dst_rect, self.lut, self.interpolate
+            self._get_display_data(),
+            src_rect,
+            self._offscreen,
+            dst_rect,
+            self.lut,
+            self.interpolate,
         )
         qrect = QC.QRectF(QC.QPointF(dest[0], dest[1]), QC.QPointF(dest[2], dest[3]))
         painter.drawImage(qrect, self._image, qrect)
@@ -797,10 +888,12 @@ def export_roi(
         """
         if apply_lut:
             a, b, _bg, _cmap = self.lut
+            data = self._get_display_data()
         else:
             a, b = 1.0, 0.0
+            data = self.data
         interp = self.interpolate if apply_interpolation else (INTERP_NEAREST,)
-        _scale_rect(self.data, src_rect, dst_image, dst_rect, (a, b, None), interp)
+        _scale_rect(data, src_rect, dst_image, dst_rect, (a, b, None), interp)
 
     # ---- QwtPlotItem API -----------------------------------------------------
     def draw(
@@ -1170,7 +1263,7 @@ def get_histogram(
     def __process_cross_section(self, ydata, apply_lut):
         if apply_lut:
             a, b, _bg, _cmap = self.lut
-            return (ydata * a + b).clip(0, LUT_MAX)
+            return (self._to_lut_space(ydata) * a + b).clip(0, LUT_MAX)
         else:
             return ydata
 
@@ -1283,6 +1376,7 @@ class RawImageItem(BaseImageItem):
         IVoiImageItemType,
         ISerializableType,
     )
+    _ZAXIS_LOG_SUPPORTED = True
 
     # ---- BaseImageItem API ---------------------------------------------------
     def get_default_param(self) -> RawImageParam:

plotpy/items/image/misc.py

@@ -71,6 +71,8 @@ class QuadGridItem(RawImageItem):
     """
 
     __implements__ = (IBasePlotItem, IBaseImageItem, IHistDataSource, IVoiImageItemType)
+    # Quadrilaterals are drawn from the data itself, without the log10 data
+    _ZAXIS_LOG_SUPPORTED = False
 
     def __init__(
         self,

plotpy/items/image/standard.py

@@ -359,17 +359,14 @@ def draw_image(
         src2 = self._rescale_src_rect(src_rect)
         dst_rect = tuple([int(i) for i in dst_rect])
 
-        # Not the most efficient way to do it, but it works...
-        # --------------------------------------------------------------------------
-        if self.get_zaxis_log_state():
-            data = self._log_data
-        else:
-            data = self.data
-        # --------------------------------------------------------------------------
-
         try:
             dest = _scale_rect(
-                data, src2, self._offscreen, dst_rect, self.lut, self.interpolate
+                self._get_display_data(),
+                src2,
+                self._offscreen,
+                dst_rect,
+                self.lut,
+                self.interpolate,
             )
         except ValueError:
             # This exception is raised when zooming unreasonably inside a pixel
@@ -403,12 +400,14 @@ def export_roi(
         """
         if apply_lut:
             a, b, _bg, _cmap = self.lut
+            data = self._get_display_data()
         else:
             a, b = 1.0, 0.0
+            data = self.data
         interp = self.interpolate if apply_interpolation else (INTERP_NEAREST,)
         rescaled_src = self._rescale_src_rect(src_rect)
         _scale_rect(
-            self.data,
+            data,
             rescaled_src,
             dst_image,
             dst_rect,
@@ -657,12 +656,13 @@ def draw_image(
             return
         xytr = self.x, self.y, src_rect
         dst_rect = tuple([int(i) for i in dst_rect])
-        if self.get_zaxis_log_state():
-            data = self._log_data
-        else:
-            data = self.data
         dest = _scale_xy(
-            data, xytr, self._offscreen, dst_rect, self.lut, self.interpolate
+            self._get_display_data(),
+            xytr,
+            self._offscreen,
+            dst_rect,
+            self.lut,
+            self.interpolate,
         )
         qrect = QC.QRectF(QC.QPointF(dest[0], dest[1]), QC.QPointF(dest[2], dest[3]))
         painter.drawImage(qrect, self._image, qrect)
@@ -692,12 +692,14 @@ def export_roi(
         """
         if apply_lut:
             lut = self.lut
+            data = self._get_display_data()
         else:
             a, b = 1.0, 0.0
             lut = (a, b, None, np.zeros((1,), np.uint32))
+            data = self.data
         interp = self.interpolate if apply_interpolation else (INTERP_NEAREST,)
         xytr = self.x, self.y, src_rect
-        _scale_xy(self.data, xytr, dst_image, dst_rect, lut, interp)
+        _scale_xy(data, xytr, dst_image, dst_rect, lut, interp)
 
     def get_pixel_coordinates(self, xplot: float, yplot: float) -> tuple[float, float]:
         """Get pixel coordinates from plot coordinates
@@ -835,6 +837,8 @@ class RGBImageItem(ImageItem):
     """
 
     __implements__ = (IBasePlotItem, IBaseImageItem, ISerializableType)
+    # RGB images have no colormap
+    _ZAXIS_LOG_SUPPORTED = False
 
     def __init__(
         self, data: np.ndarray | None = None, param: RGBImageParam | None = None