readme.4

Signed-off-by: Cary Phillips <[email protected]>

src/wrappers/python/README.md

@@ -72,26 +72,129 @@ The "Hello, World" image writer:
     height, width = (20, 10)
     RGB = np.random.rand(height, width, 3).astype('f')
 
-    import OpenEXR, Imath
-    from array import array
-
-    width = 10
-    height = 10
-    size = width * height
-
-    h = OpenEXR.Header(width,height)
-    h['channels'] = {'R' : Imath.Channel(Imath.PixelType(Imath.PixelType.FLOAT)),
-                     'G' : Imath.Channel(Imath.PixelType(Imath.PixelType.FLOAT)),
-                     'B' : Imath.Channel(Imath.PixelType(Imath.PixelType.FLOAT)),
-                     'A' : Imath.Channel(Imath.PixelType(Imath.PixelType.FLOAT))} 
-    o = OpenEXR.OutputFile("hello.exr", h)
-    r = array('f', [n for n in range(size*0,size*1)]).tobytes()
-    g = array('f', [n for n in range(size*1,size*2)]).tobytes()
-    b = array('f', [n for n in range(size*2,size*3)]).tobytes()
-    a = array('f', [n for n in range(size*3,size*4)]).tobytes()
-    channels = {'R' : r, 'G' : g, 'B' : b, 'A' : a}
-    o.writePixels(channels)
-    o.close()
+    channels = { "RGB" : RGB }
+    header = { "compression" : OpenEXR.ZIP_COMPRESSION,
+               "type" : OpenEXR.scanlineimage }
+
+    with OpenEXR.File(header, channels) as outfile:
+        outfile.write("readme.exr")
+
+Or alternatively, construct the same output file via separate pixel arrays
+for each channel:
+
+    # Generate arrays for R, G, and B channels with random values
+    height, width = (20, 10)
+    R = np.random.rand(height, width).astype('f')
+    G = np.random.rand(height, width).astype('f')
+    B = np.random.rand(height, width).astype('f')
+    channels = { "R" : R, "G" : G, "B" : B }
+    header = { "compression" : OpenEXR.ZIP_COMPRESSION,
+               "type" : OpenEXR.scanlineimage }
+
+    with OpenEXR.File(header, channels) as outfile:
+        outfile.write("readme.exr")
+
+The corresponding example of reading an image is:
+
+    with OpenEXR.File("readme.exr") as infile:
+
+        RGB = infile.channels()["RGB"].pixels
+        height, width, _ = RGB.shape
+        for y in range(height):
+            for x in range(width):
+                pixel = tuple(RGB[y, x])
+                print(f"pixel[{y}][{x}]={pixel}")
+
+Or alternatively, read the data as separate arrays for each channel:
+
+    with OpenEXR.File("readme.exr", separate_channels=True) as infile:
+
+        header = infile.header()
+        print(f"type={header['type']}")
+        print(f"compression={header['compression']}")
+
+        R = infile.channels()["R"].pixels
+        G = infile.channels()["G"].pixels
+        B = infile.channels()["B"].pixels
+        height, width = R.shape
+        for y in range(height):
+            for x in range(width):
+                pixel = (R[y, x], G[y, x], B[y, x])
+                print(f"pixel[{y}][{x}]={pixel}")
+
+To modify the header metadata in a file:
+
+    with OpenEXR.File("readme.exr") as f:
+        
+        f.header()["displayWindow"] = ((3,4),(5,6))
+        f.header()["screenWindowCenter"] = np.array([1.0,2.0],'float32')
+        f.header()["comments"] = "test image"
+        f.header()["longitude"] = -122.5
+        f.write("readme_modified.exr")
+
+        with OpenEXR.File("readme_modified.exr") as o:
+            dw = o.header()["displayWindow"]
+            assert (tuple(dw[0]), tuple(dw[1])) == ((3,4),(5,6))
+            swc = o.header()["screenWindowCenter"]
+            assert tuple(swc) == (1.0, 2.0)
+            assert o.header()["comments"] == "test image"
+            assert o.header()["longitude"] == -122.5
+
+Note that OpenEXR's Imath-based vector and matrix attribute values
+appear in the header dictionary as 2-element, 3-element, 3x3, 4x4
+numpy arrays, and bounding boxes appear as tuples of 2-element arrays,
+or tuples for convenience.
+
+To read and write a multi-part file, use a list of ``Part`` objects:
+
+    height, width = (20, 10)
+    Z0 = np.zeros((height, width), dtype='f')
+    Z1 = np.ones((height, width), dtype='f')
+
+    P0 = OpenEXR.Part({}, {"Z" : Z0 })
+    P1 = OpenEXR.Part({}, {"Z" : Z1 })
+
+    f = OpenEXR.File([P0, P1])
+    f.write("readme_2part.exr")
+
+    with OpenEXR.File("readme_2part.exr") as o:
+        assert o.parts[0].name() == "Part0"
+        assert o.parts[0].width() == 10
+        assert o.parts[0].height() == 20
+        assert o.parts[1].name() == "Part1"
+        assert o.parts[1].width() == 10
+        assert o.parts[1].height() == 20
+
+Deep data is stored in a numpy array whose entries are numpy
+arrays. Construct a numpy array with a ``dtype`` of ``object``, and
+assign each entry a numpy array holding the samples. Each pixel can
+have a different number of samples, including ``None`` for no data,
+but all channels in a given part must have the same number of samples.
+
+    height, width = (20, 10)
+
+    Z = np.empty((height, width), dtype=object)
+    for y in range(height):
+        for x in range(width):
+            Z[y, x] = np.array([y*width+x], dtype='uint32')
+
+    channels = { "Z" : Z }
+    header = { "compression" : OpenEXR.ZIPS_COMPRESSION,
+               "type" : OpenEXR.deepscanline }
+    with OpenEXR.File(header, channels) as outfile:
+        outfile.write("readme_test_tiled_deep.exr")
+
+To read a deep file:
+
+    with OpenEXR.File("readme_test_tiled_deep.exr") as infile:
+
+        Z = infile.channels()["Z"].pixels
+        height, width = Z.shape
+        for y in range(height):
+            for x in range(width):
+                for z in Z[y,x]:
+                    print(f"deep sample at {y},{x}: {z}")
+
 
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