Apply a functor to each pixel in an Image

afw supports for_each_pixel as a way to process each pixel in an Image, in a similar way to the STL's for_each. The name doesn't follow the LSST C++ guidelines, but in this case I felt that conformity to the spirit of the STL was more important. There are variants of for_each_pixel corresponding to setting a pixel to a function, setting it to a function of an Image, and setting it to a function of its value and a second Image's pixel value. The selection of which of these operations is desired is done by requiring the functor to inherit from a class such as pixelOp0 or pixelOp1XY, each of which is a std::function with a virtual operator() added.

for_each_pixel(Image<LhsT> &lhs, pixelOp0<LhsT> const& func)

Set each pixel in lhs to the value of func.

for_each_pixel(Image<LhsT> &lhs, pixelOp1<LhsT> const& func)

Set each pixel in lhs to the value of func(lhs).

for_each_pixel(Image<LhsT> &lhs, pixelOp1XY<LhsT> const& func)

Set each pixel in lhs to the value of func(x, y, lhs).

for_each_pixel(Image<LhsT> &lhs, Image<RhsT> const& rhs, pixelOp1<RhsT> const& func)

Set each pixel in lhs to the value of func(lhs).

for_each_pixel(Image<LhsT> &lhs, Image<RhsT> const& rhs, pixelOp2<Lhs, RhsT> const& func)

Set each pixel in lhs to the value of func(lhs, rhs).

for_each_pixel(Image<LhsT> &lhs, Image<RhsT> const& rhs, pixelOp2XY<Lhs, RhsT> const& func)

Set each pixel in lhs to the value of func(x, y, lhs, rhs).

Example of using for_each_pixel

This code is in forEachPixel.cc.

Include needed header file, and define a namespace alias

Here's the simplest possible functor, simply setting each pixel to 0. Note that operator() is declared const, as we pass these functors by (const) reference. If this surprises you, take a look at Meyers, Effective STL, Item 38.

This one's a bit more interesting. We save a value in the constructor, and use it to set each pixel. It's analogous to std::fill, but if I called it fill then following a using namespace std; the compiler would complain about ambiguity; it's simpler just to use a different name.

Here are examples of pixelOp1 and pixelOp2.

A functor designed to add a Gaussian to an image

Declare a couple of Images to play with

Apply erase to each pixel in img1, setVal to each pixel in img2, set img1 = img2 + 1, and finally img1 /= img1

Add a Gaussian to the image, centered at (xc, yc) and with central intensity 1000.