Fix px.imshow ignoring zmin/zmax when the image contains NaN

CHANGELOG.md

@@ -7,6 +7,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 - Fix concurrent first access to lazily initialized graph object properties, which could raise `ValueError("Invalid value")` [[#3441](https://github.com/plotly/plotly.py/issues/3441)], with thanks to @hb1915 for the contribution!
 - Fix `px.sunburst`, `px.treemap` and `px.icicle` listing sectors in a different order on every run when `path` is used with a Polars DataFrame; sectors now follow their order of first appearance for all dataframe backends [[#5765](https://github.com/plotly/plotly.py/issues/5765)], with thanks to @Irahan2 for the contribution!
+- Fix `px.imshow` ignoring `zmin`/`zmax` when only one of them is passed and the image contains NaN values, since the missing bound was computed as NaN [[#4299](https://github.com/plotly/plotly.py/issues/4299)], with thanks to @MohammadHijjawi97 for the contribution!
 
 
 ## [7.1.0] - 2026-09-15

plotly/express/_imshow.py

@@ -412,9 +412,9 @@ def imshow(
     if contrast_rescaling == "minmax":
         # When using binary_string and minmax we need to set zmin and zmax to rescale the image
         if (zmin is not None or binary_string) and zmax is None:
-            zmax = img.max()
+            zmax = np.nanmax(img)
         if (zmax is not None or binary_string) and zmin is None:
-            zmin = img.min()
+            zmin = np.nanmin(img)
     else:
         # For uint8 data and infer we let zmin and zmax to be None if passed as None
         if zmax is None and img.dtype != np.uint8:

tests/test_optional/test_px/test_imshow.py

@@ -183,6 +183,17 @@ def test_zmin_zmax_range_color():
     assert fig.layout.coloraxis.cmax == 0.8
 
 
+def test_zmin_zmax_nan_data():
+    # NaN values should be ignored when inferring the missing bound
+    img = np.array([[1.0, 2.0], [3.0, np_nan()]])
+    fig = px.imshow(img, zmax=2)
+    assert fig.layout.coloraxis.cmin == 1.0
+    assert fig.layout.coloraxis.cmax == 2.0
+    fig = px.imshow(img, zmin=2)
+    assert fig.layout.coloraxis.cmin == 2.0
+    assert fig.layout.coloraxis.cmax == 3.0
+
+
 def test_zmin_zmax_range_color_source():
     img = img_gray / 100.0
     fig1 = px.imshow(img, zmin=0.2, zmax=0.8, binary_string=True)