Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards


// Copyright 2005-2007 Adobe Systems Incorporated
// Distributed under the Boost Software License, Version 1.0
// See accompanying file LICENSE_1_0.txt or copy at

#include <boost/gil/extension/io/jpeg.hpp>

#include <algorithm>

// This test file demonstrates how to use packed pixel formats in GIL.
// A "packed" pixel is a pixel whose channels are bit ranges.
// Here we create an RGB image whose pixel has 16-bits, such as:
// bits [0..6] are the blue channel
// bits [7..13] are the green channel
// bits [14..15] are the red channel
// We read a regular 8-bit RGB image, convert it to packed BGR772, convert it back to 8-bit RGB and save it to a file.
// Since the red channel is only two bits the color loss should be observable in the result
// This test file also demonstrates how to use bit-aligned images - these are images whose pixels themselves are not byte aligned.
// For example, an rgb222 image has a pixel whose size is 6 bits. Bit-aligned images are more complicated than packed images. They
// require a special proxy class to represent pixel reference and pixel iterator (packed images use C++ reference and C pointer respectively).
// The alignment parameter in the constructor of bit-aligned images is in bit units. For example, if you want your bit-aligned image to have 4-byte
// alignment of its rows use alignment of 32, not 4.
// To demonstrate that image view transformations work on packed images, we save the result transposed.

using namespace boost;
using namespace boost::gil;

int main() {
    bgr8_image_t img;
    read_image("test.jpg",img, jpeg_tag{});

    // define a bgr772 image. It is a "packed" image - its channels are not byte-aligned, but its pixels are.

    using bgr772_image_t = packed_image3_type<uint16_t, 7,7,2, bgr_layout_t>::type;
    bgr772_image_t bgr772_img(img.dimensions());

    // Save the result. JPEG I/O does not support the packed pixel format, so convert it back to 8-bit RGB
    write_view("out-packed_pixel_bgr772.jpg",color_converted_view<bgr8_pixel_t>(transposed_view(const_view(bgr772_img))), jpeg_tag{});

    // define a gray1 image (one-bit per pixel). It is a "bit-aligned" image - its pixels are not byte aligned.

    using gray1_image_t = bit_aligned_image1_type<1, gray_layout_t>::type;
    gray1_image_t gray1_img(img.dimensions());

    // Save the result. JPEG I/O does not support the packed pixel format, so convert it back to 8-bit RGB
    write_view("out-packed_pixel_gray1.jpg",color_converted_view<gray8_pixel_t>(transposed_view(const_view(gray1_img))), jpeg_tag{});

    return 0;