move array_to_imagestr function to be part of public API (#2879)

* move array_to_imagestr function to be part of public API

* renamed function

packages/python/plotly/_plotly_utils/data_utils.py

@@ -0,0 +1,75 @@
+from io import BytesIO
+import base64
+from .png import Writer, from_array
+
+try:
+    from PIL import Image
+
+    pil_imported = True
+except ImportError:
+    pil_imported = False
+
+
+def image_array_to_data_uri(img, backend="pil", compression=4, ext="png"):
+    """Converts a numpy array of uint8 into a base64 png or jpg string.
+
+    Parameters
+    ----------
+    img: ndarray of uint8
+        array image
+    backend: str
+        'auto', 'pil' or 'pypng'. If 'auto', Pillow is used if installed,
+        otherwise pypng.
+    compression: int, between 0 and 9
+        compression level to be passed to the backend
+    ext: str, 'png' or 'jpg'
+        compression format used to generate b64 string
+    """
+    # PIL and pypng error messages are quite obscure so we catch invalid compression values
+    if compression < 0 or compression > 9:
+        raise ValueError("compression level must be between 0 and 9.")
+    alpha = False
+    if img.ndim == 2:
+        mode = "L"
+    elif img.ndim == 3 and img.shape[-1] == 3:
+        mode = "RGB"
+    elif img.ndim == 3 and img.shape[-1] == 4:
+        mode = "RGBA"
+        alpha = True
+    else:
+        raise ValueError("Invalid image shape")
+    if backend == "auto":
+        backend = "pil" if pil_imported else "pypng"
+    if ext != "png" and backend != "pil":
+        raise ValueError("jpg binary strings are only available with PIL backend")
+
+    if backend == "pypng":
+        ndim = img.ndim
+        sh = img.shape
+        if ndim == 3:
+            img = img.reshape((sh[0], sh[1] * sh[2]))
+        w = Writer(
+            sh[1], sh[0], greyscale=(ndim == 2), alpha=alpha, compression=compression
+        )
+        img_png = from_array(img, mode=mode)
+        prefix = "data:image/png;base64,"
+        with BytesIO() as stream:
+            w.write(stream, img_png.rows)
+            base64_string = prefix + base64.b64encode(stream.getvalue()).decode("utf-8")
+    else:  # pil
+        if not pil_imported:
+            raise ImportError(
+                "pillow needs to be installed to use `backend='pil'. Please"
+                "install pillow or use `backend='pypng'."
+            )
+        pil_img = Image.fromarray(img)
+        if ext == "jpg" or ext == "jpeg":
+            prefix = "data:image/jpeg;base64,"
+            ext = "jpeg"
+        else:
+            prefix = "data:image/png;base64,"
+            ext = "png"
+        with BytesIO() as stream:
+            pil_img.save(stream, format=ext, compress_level=compression)
+            base64_string = prefix + base64.b64encode(stream.getvalue()).decode("utf-8")
+    return base64_string

packages/python/plotly/plotly/express/_imshow.py

@@ -1,94 +1,21 @@
 import plotly.graph_objs as go
 from _plotly_utils.basevalidators import ColorscaleValidator
 from ._core import apply_default_cascade
-from io import BytesIO
-import base64
 from .imshow_utils import rescale_intensity, _integer_ranges, _integer_types
 import pandas as pd
-from .png import Writer, from_array
 import numpy as np
+from plotly.utils import image_array_to_data_uri
 
 try:
     import xarray
 
     xarray_imported = True
 except ImportError:
     xarray_imported = False
-try:
-    from PIL import Image
-
-    pil_imported = True
-except ImportError:
-    pil_imported = False
 
 _float_types = []
 
 
-def _array_to_b64str(img, backend="pil", compression=4, ext="png"):
-    """Converts a numpy array of uint8 into a base64 png string.
-
-    Parameters
-    ----------
-    img: ndarray of uint8
-        array image
-    backend: str
-        'auto', 'pil' or 'pypng'. If 'auto', Pillow is used if installed,
-        otherwise pypng.
-    compression: int, between 0 and 9
-        compression level to be passed to the backend
-    ext: str, 'png' or 'jpg'
-        compression format used to generate b64 string
-    """
-    # PIL and pypng error messages are quite obscure so we catch invalid compression values
-    if compression < 0 or compression > 9:
-        raise ValueError("compression level must be between 0 and 9.")
-    alpha = False
-    if img.ndim == 2:
-        mode = "L"
-    elif img.ndim == 3 and img.shape[-1] == 3:
-        mode = "RGB"
-    elif img.ndim == 3 and img.shape[-1] == 4:
-        mode = "RGBA"
-        alpha = True
-    else:
-        raise ValueError("Invalid image shape")
-    if backend == "auto":
-        backend = "pil" if pil_imported else "pypng"
-    if ext != "png" and backend != "pil":
-        raise ValueError("jpg binary strings are only available with PIL backend")
-
-    if backend == "pypng":
-        ndim = img.ndim
-        sh = img.shape
-        if ndim == 3:
-            img = img.reshape((sh[0], sh[1] * sh[2]))
-        w = Writer(
-            sh[1], sh[0], greyscale=(ndim == 2), alpha=alpha, compression=compression
-        )
-        img_png = from_array(img, mode=mode)
-        prefix = "data:image/png;base64,"
-        with BytesIO() as stream:
-            w.write(stream, img_png.rows)
-            base64_string = prefix + base64.b64encode(stream.getvalue()).decode("utf-8")
-    else:  # pil
-        if not pil_imported:
-            raise ImportError(
-                "pillow needs to be installed to use `backend='pil'. Please"
-                "install pillow or use `backend='pypng'."
-            )
-        pil_img = Image.fromarray(img)
-        if ext == "jpg" or ext == "jpeg":
-            prefix = "data:image/jpeg;base64,"
-            ext = "jpeg"
-        else:
-            prefix = "data:image/png;base64,"
-            ext = "png"
-        with BytesIO() as stream:
-            pil_img.save(stream, format=ext, compress_level=compression)
-            base64_string = prefix + base64.b64encode(stream.getvalue()).decode("utf-8")
-    return base64_string
-
-
 def _vectorize_zvalue(z, mode="max"):
     alpha = 255 if mode == "max" else 0
     if z is None:
@@ -422,7 +349,7 @@ def imshow(
                         for ch in range(img.shape[-1])
                     ]
                 )
-            img_str = _array_to_b64str(
+            img_str = image_array_to_data_uri(
                 img_rescaled,
                 backend=binary_backend,
                 compression=binary_compression_level,

packages/python/plotly/plotly/utils.py

@@ -4,7 +4,7 @@
 from pprint import PrettyPrinter
 
 from _plotly_utils.utils import *
-
+from _plotly_utils.data_utils import *
 
 # Pretty printing
 def _list_repr_elided(v, threshold=200, edgeitems=3, indent=0, width=80):