# colormap

**Repository Path**: dong_fangzhou/colormap

## Basic Information

- **Project Name**: colormap
- **Description**: No description available
- **Primary Language**: Unknown
- **License**: GPL-2.0
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2021-10-11
- **Last Updated**: 2021-10-11

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

colormap
========

This repository contains a number of somewhat connected utilities which
originated in the development of the [*svm-order-params*][3] project, but are
independent from this application. It's components are split amongs several headers:

* `color.hpp`: Provides a `colormap::color` class representing a grayscale, RGB,
  or RGBA color, including the ability to mix colors.
* `map.hpp`: Provides the `colormap::map`, a functor that maps real numbers to a
  color by interpolating between colors at pre-defined support points.
* `palettes.hpp`: Defines a variety of ready-to-use `colormap::map`s, mostly
  inspired by [ColorBrewer][4] and the [gnuplot-palettes][5] repository by
  *Gnuplotting* (a.k.a. Hagen Wierstorf). The palettes are exposed through a
  global variable `colormap::palettes`, a `std::map` that maps names
  (`std::string`s) to `colormap::map`s.
* `itadpt/map_iterator_adapter.hpp`: Defines an iterator adapter that lazily
  applies a functor on a base iterator upon dereferenciation. Notable API are
  the non-member functions
  - `map_iterator(BaseIterator, Functor&)` which returns a
    `map_iterator_adapter<BaseIterator, Functor>`, and
  - `map(Container const&, Functor&)` which returns a quasi-container object
    `mapped<Container, Functor>`.
* `grid.hpp`: Provides a class `colormap::grid` which represents
  multidimensional uniform grids which can be initialized very easily and are
  cheap and iterable.
* `pixmap.hpp`: Provides a class `colormap::pixmap` which can write iterators
  over `color`s to disk in PPM (or PGM) format, both in binary, and in ASCII
  form.


Using colormaps
---------------

The following code snippet showcases some of the features of the headers in this
repository. For a compilable example, see [`test/mandelbrot.cpp`][1].

```cpp
using namespace colormap;

// set up the grid: 701 x 401 grid points (pixels) representing the region
// [-2.5, 1] x [-1, 1].
grid<2, major_order::col> g { {701, {-2.5, 1.}}, {401, {-1., 1.}} };
using grid_point_t = typename decltype(g)::grid_point_type;

// set up the functor to be visualized on the grid, e.g. the mandelbrot set
auto mandelbrot = [] (grid_point_t c_arr) { /* omitted */ };

// Iterator adapter mapping grid points to function values.
// Result is a `mapped` object that behave like a container.
auto val = itadpt::map(g, mandelbrot);

// find the maximum value
double max = *std::max_element(val.begin(), val.end());

// get a colormap and rescale it
auto pal = palettes.at("inferno").rescale(1, max);
// and use it to map the values to colors
auto pix = itadpt::map(val, pal);

// Construct a PPM object from the `mapped` object `pix`. Color space is
// inferred from color type of pix. "inferno" is an RGB palette, so `pmap`
// will represent a PPM image. For a grayscale colormap, it would result in
// a PGM image.
pixmap<decltype(pix.begin())> pmap(pix.begin(), g.shape());

std::ofstream os("appleman." + pmap.file_extension(),
                 std::ios_base::binary);
pmap.write_binary(os);
```

produces the image `appleman.ppm`:

![appleman][2]

Color Palettes
--------------

![palettes][6]

License
-------

Copyright (C) 2018-2019  Jonas Greitemann

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.



[1]: test/mandelbrot.cpp
[2]: doc/appleman.png
[3]: https://gitlab.physik.uni-muenchen.de/LDAP_ls-schollwoeck/svm-order-params
[4]: http://colorbrewer2.org/
[5]: https://github.com/Gnuplotting/gnuplot-palettes
[6]: doc/palettes_labelled.png