Python Image and Rectangle Scaling (#1488)

* added scale_image python binding which returns an image resized by the provided scale factor

* added scale_rect for rectangle and drectangle. returns a rectangle scaled by the provided scaling factor

* - do not cast scale_rect coordinates to long for drectangle
- document scale_rect for drectangle and rectangle in _abstract.h
- change python binding scale_image to resize_image
- update documentation for resize_image to describe behaviour

dlib/geometry/drectangle.h

@@ -441,6 +441,20 @@ namespace dlib
         return shrink_rect(rect, -width, -height);
     }
 
+    inline const drectangle scale_rect (
+        const drectangle& rect,
+        double scale
+    )
+    {
+        DLIB_ASSERT(scale > 0, "scale factor must be > 0");
+
+        double l = rect.left() * scale;
+        double t = rect.top() * scale;
+        double r = rect.right() * scale;
+        double b = rect.bottom() * scale;
+        return drectangle(l, t, r, b);
+    }
+
     inline drectangle set_rect_area (
         const drectangle& rect,
         double area

dlib/geometry/drectangle_abstract.h

@@ -585,6 +585,20 @@ namespace dlib
               (i.e. grows the given drectangle by expanding its border)
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    const drectangle scale_rect (
+        const drectangle& rect,
+        double scale
+    );
+    /*!
+        requires
+            - scale > 0
+        ensures
+            - return drectangle(rect.left() * scale, rect.top() * scale, rect.right() * scale, rect.bottom() * scale)
+              (i.e. resizes the given rectangle by multiplying all side coordinates with a scale factor)
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     drectangle set_rect_area (

dlib/geometry/rectangle.h

@@ -641,6 +641,22 @@ namespace dlib
         return shrink_rect(rect, -width, -height);
     }
 
+// ----------------------------------------------------------------------------------------
+
+    inline const rectangle scale_rect (
+        const rectangle& rect,
+        double scale
+    )
+    {
+        DLIB_ASSERT(scale > 0, "scale factor must be > 0");
+
+        long l = (long)std::round(rect.left()*scale);
+        long t = (long)std::round(rect.top()*scale);
+        long r = (long)std::round(rect.right()*scale);
+        long b = (long)std::round(rect.bottom()*scale);
+        return rectangle(l, t, r, b);
+    }
+
 // ----------------------------------------------------------------------------------------
 
     inline const rectangle translate_rect (

dlib/geometry/rectangle_abstract.h

@@ -609,6 +609,20 @@ namespace dlib
               (i.e. grows the given rectangle by expanding its border)
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    const rectangle scale_rect (
+        const rectangle& rect,
+        double scale
+    );
+    /*!
+        requires
+            - scale > 0
+        ensures
+            - return rectangle(rect.left() * scale, rect.top() * scale, rect.right() * scale, rect.bottom() * scale)
+              (i.e. resizes the given rectangle by multiplying all side coordinates with a scale factor)
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     const rectangle translate_rect (

tools/python/src/image2.cpp

@@ -28,6 +28,20 @@ numpy_image<T> py_resize_image (
 
 // ----------------------------------------------------------------------------------------
 
+template <typename T>
+numpy_image<T> py_scale_image (
+    const numpy_image<T>& img,
+    double scale
+)
+{
+    DLIB_CASSERT(scale > 0, "Scale factor must be greater than 0");
+    numpy_image<T> out = img;
+    resize_image(scale, out);
+    return out;
+}
+
+// ----------------------------------------------------------------------------------------
+
 template <typename T>
 numpy_image<T> py_equalize_histogram (
     const numpy_image<T>& img
@@ -535,6 +549,15 @@ void bind_image_classes2(py::module& m)
     m.def("resize_image", &py_resize_image<float>, py::arg("img"), py::arg("rows"), py::arg("cols"));
     m.def("resize_image", &py_resize_image<double>, docs, py::arg("img"), py::arg("rows"), py::arg("cols"));
     m.def("resize_image", &py_resize_image<rgb_pixel>, docs, py::arg("img"), py::arg("rows"), py::arg("cols"));
+    m.def("resize_image", &py_scale_image<int8_t>, py::arg("img"), py::arg("scale"));
+    m.def("resize_image", &py_scale_image<int16_t>, py::arg("img"), py::arg("scale"));
+    m.def("resize_image", &py_scale_image<int32_t>, py::arg("img"), py::arg("scale"));
+    m.def("resize_image", &py_scale_image<int64_t>, py::arg("img"), py::arg("scale"));
+    m.def("resize_image", &py_scale_image<float>, py::arg("img"), py::arg("scale"));
+    m.def("resize_image", &py_scale_image<double>, py::arg("img"), py::arg("scale"));
+    m.def("resize_image", &py_scale_image<rgb_pixel>, py::arg("img"), py::arg("scale"),
+        "Resizes img, using bilinear interpolation, to have the new size (img rows * scale, img cols * scale)"
+        );
 
     register_extract_image_chip(m);
 

tools/python/src/rectangles.cpp

@@ -290,6 +290,11 @@ ensures \n\
   (i.e. grows the given rectangle by expanding its border by num)",
         py::arg("rect"), py::arg("num"));
 
+    m.def("scale_rect", [](const rectangle& rect, double scale){return scale_rect(rect,scale);},
+"- return scale_rect(rect, scale) \n\
+(i.e. resizes the given rectangle by a scale factor)",
+        py::arg("rect"), py::arg("scale"));
+
     m.def("centered_rect", [](const point& p, unsigned long width, unsigned long height) {
         return centered_rect(p, width, height); },
         py::arg("p"), py::arg("width"), py::arg("height"));