Allow GaussianBlur and BoxBlur to accept a sequence of x and y radii

Tests/test_box_blur.py

@@ -22,7 +22,7 @@ def test_imageops_box_blur():
 
 
 def box_blur(image, radius=1, n=1):
-    return image._new(image.im.box_blur(radius, n))
+    return image._new(image.im.box_blur((radius, radius), n))
 
 
 def assert_image(im, data, delta=0):

Tests/test_image_filter.py

@@ -24,8 +24,10 @@
         ImageFilter.ModeFilter,
         ImageFilter.GaussianBlur,
         ImageFilter.GaussianBlur(5),
+        ImageFilter.GaussianBlur((2, 5)),
         ImageFilter.BoxBlur(0),
         ImageFilter.BoxBlur(5),
+        ImageFilter.BoxBlur((2, 5)),
         ImageFilter.UnsharpMask,
         ImageFilter.UnsharpMask(10),
     ),
@@ -185,12 +187,21 @@ def test_consistency_5x5(mode):
             assert_image_equal(source.filter(kernel), reference)
 
 
-def test_invalid_box_blur_filter():
+@pytest.mark.parametrize(
+    "radius",
+    (
+        -2,
+        (-2, -2),
+        (-2, 2),
+        (2, -2),
+    ),
+)
+def test_invalid_box_blur_filter(radius):
     with pytest.raises(ValueError):
-        ImageFilter.BoxBlur(-2)
+        ImageFilter.BoxBlur(radius)
 
     im = hopper()
     box_blur_filter = ImageFilter.BoxBlur(2)
-    box_blur_filter.radius = -2
+    box_blur_filter.radius = radius
     with pytest.raises(ValueError):
         im.filter(box_blur_filter)

src/PIL/ImageFilter.py

@@ -157,7 +157,8 @@ class GaussianBlur(MultibandFilter):
     approximates a Gaussian kernel. For details on accuracy see
     <https://www.mia.uni-saarland.de/Publications/gwosdek-ssvm11.pdf>
 
-    :param radius: Standard deviation of the Gaussian kernel.
+    :param radius: Standard deviation of the Gaussian kernel. Either a sequence of two
+                   numbers for x and y, or a single number for both.
     """
 
     name = "GaussianBlur"
@@ -166,7 +167,10 @@ def __init__(self, radius=2):
         self.radius = radius
 
     def filter(self, image):
-        return image.gaussian_blur(self.radius)
+        xy = self.radius
+        if not isinstance(xy, (tuple, list)):
+            xy = (xy, xy)
+        return image.gaussian_blur(xy)
 
 
 class BoxBlur(MultibandFilter):
@@ -176,21 +180,29 @@ class BoxBlur(MultibandFilter):
     which runs in linear time relative to the size of the image
     for any radius value.
 
-    :param radius: Size of the box in one direction. Radius 0 does not blur,
-                   returns an identical image. Radius 1 takes 1 pixel
-                   in each direction, i.e. 9 pixels in total.
+    :param radius: Size of the box in a direction. Either a sequence of two numbers for
+                   x and y, or a single number for both.
+
+                   Radius 0 does not blur, returns an identical image.
+                   Radius 1 takes 1 pixel in each direction, i.e. 9 pixels in total.
     """
 
     name = "BoxBlur"
 
     def __init__(self, radius):
-        if radius < 0:
+        xy = radius
+        if not isinstance(xy, (tuple, list)):
+            xy = (xy, xy)
+        if xy[0] < 0 or xy[1] < 0:
             msg = "radius must be >= 0"
             raise ValueError(msg)
         self.radius = radius
 
     def filter(self, image):
-        return image.box_blur(self.radius)
+        xy = self.radius
+        if not isinstance(xy, (tuple, list)):
+            xy = (xy, xy)
+        return image.box_blur(xy)
 
 
 class UnsharpMask(MultibandFilter):

src/_imaging.c

@@ -1075,9 +1075,9 @@ _gaussian_blur(ImagingObject *self, PyObject *args) {
     Imaging imIn;
     Imaging imOut;
 
-    float radius = 0;
+    float xradius, yradius;
     int passes = 3;
-    if (!PyArg_ParseTuple(args, "f|i", &radius, &passes)) {
+    if (!PyArg_ParseTuple(args, "(ff)|i", &xradius, &yradius, &passes)) {
         return NULL;
     }
 
@@ -1087,7 +1087,7 @@ _gaussian_blur(ImagingObject *self, PyObject *args) {
         return NULL;
     }
 
-    if (!ImagingGaussianBlur(imOut, imIn, radius, passes)) {
+    if (!ImagingGaussianBlur(imOut, imIn, xradius, yradius, passes)) {
         ImagingDelete(imOut);
         return NULL;
     }
@@ -2131,9 +2131,9 @@ _box_blur(ImagingObject *self, PyObject *args) {
     Imaging imIn;
     Imaging imOut;
 
-    float radius;
+    float xradius, yradius;
     int n = 1;
-    if (!PyArg_ParseTuple(args, "f|i", &radius, &n)) {
+    if (!PyArg_ParseTuple(args, "(ff)|i", &xradius, &yradius, &n)) {
         return NULL;
     }
 
@@ -2143,7 +2143,7 @@ _box_blur(ImagingObject *self, PyObject *args) {
         return NULL;
     }
 
-    if (!ImagingBoxBlur(imOut, imIn, radius, n)) {
+    if (!ImagingBoxBlur(imOut, imIn, xradius, yradius, n)) {
         ImagingDelete(imOut);
         return NULL;
     }

src/libImaging/BoxBlur.c

@@ -230,14 +230,14 @@ ImagingHorizontalBoxBlur(Imaging imOut, Imaging imIn, float floatRadius) {
 }
 
 Imaging
-ImagingBoxBlur(Imaging imOut, Imaging imIn, float radius, int n) {
+ImagingBoxBlur(Imaging imOut, Imaging imIn, float xradius, float yradius, int n) {
     int i;
     Imaging imTransposed;
 
     if (n < 1) {
         return ImagingError_ValueError("number of passes must be greater than zero");
     }
-    if (radius < 0) {
+    if (xradius < 0 || yradius < 0) {
         return ImagingError_ValueError("radius must be >= 0");
     }
 
@@ -266,16 +266,16 @@ ImagingBoxBlur(Imaging imOut, Imaging imIn, float radius, int n) {
     /* Apply blur in one dimension.
        Use imOut as a destination at first pass,
        then use imOut as a source too. */
-    ImagingHorizontalBoxBlur(imOut, imIn, radius);
+    ImagingHorizontalBoxBlur(imOut, imIn, xradius);
     for (i = 1; i < n; i++) {
-        ImagingHorizontalBoxBlur(imOut, imOut, radius);
+        ImagingHorizontalBoxBlur(imOut, imOut, xradius);
     }
     /* Transpose result for blur in another direction. */
     ImagingTranspose(imTransposed, imOut);
 
     /* Reuse imTransposed as a source and destination there. */
     for (i = 0; i < n; i++) {
-        ImagingHorizontalBoxBlur(imTransposed, imTransposed, radius);
+        ImagingHorizontalBoxBlur(imTransposed, imTransposed, yradius);
     }
     /* Restore original orientation. */
     ImagingTranspose(imOut, imTransposed);
@@ -285,8 +285,8 @@ ImagingBoxBlur(Imaging imOut, Imaging imIn, float radius, int n) {
     return imOut;
 }
 
-Imaging
-ImagingGaussianBlur(Imaging imOut, Imaging imIn, float radius, int passes) {
+static float
+_gaussian_blur_radius(float radius, int passes) {
     float sigma2, L, l, a;
 
     sigma2 = radius * radius / passes;
@@ -299,5 +299,16 @@ ImagingGaussianBlur(Imaging imOut, Imaging imIn, float radius, int passes) {
     a = (2 * l + 1) * (l * (l + 1) - 3 * sigma2);
     a /= 6 * (sigma2 - (l + 1) * (l + 1));
 
-    return ImagingBoxBlur(imOut, imIn, l + a, passes);
+    return l + a;
+}
+
+Imaging
+ImagingGaussianBlur(Imaging imOut, Imaging imIn, float xradius, float yradius, int passes) {
+    return ImagingBoxBlur(
+      imOut,
+      imIn,
+      _gaussian_blur_radius(xradius, passes),
+      _gaussian_blur_radius(yradius, passes),
+      passes
+    );
 }

src/libImaging/Imaging.h

@@ -309,7 +309,7 @@ ImagingFlipLeftRight(Imaging imOut, Imaging imIn);
 extern Imaging
 ImagingFlipTopBottom(Imaging imOut, Imaging imIn);
 extern Imaging
-ImagingGaussianBlur(Imaging imOut, Imaging imIn, float radius, int passes);
+ImagingGaussianBlur(Imaging imOut, Imaging imIn, float xradius, float yradius, int passes);
 extern Imaging
 ImagingGetBand(Imaging im, int band);
 extern Imaging
@@ -376,7 +376,7 @@ ImagingTransform(
 extern Imaging
 ImagingUnsharpMask(Imaging imOut, Imaging im, float radius, int percent, int threshold);
 extern Imaging
-ImagingBoxBlur(Imaging imOut, Imaging imIn, float radius, int n);
+ImagingBoxBlur(Imaging imOut, Imaging imIn, float xradius, float yradius, int n);
 extern Imaging
 ImagingColorLUT3D_linear(
     Imaging imOut,

src/libImaging/UnsharpMask.c

@@ -36,7 +36,7 @@ ImagingUnsharpMask(
 
     /* First, do a gaussian blur on the image, putting results in imOut
        temporarily. All format checks are in gaussian blur. */
-    result = ImagingGaussianBlur(imOut, imIn, radius, 3);
+    result = ImagingGaussianBlur(imOut, imIn, radius, radius, 3);
     if (!result) {
         return NULL;
     }