如何在 ImageMagick 7 / Magick++ 中读取索引/调色图像像素

Question

我正在尝试使用 Magick++ / ImageMagick 7 读取索引/调色板/颜色映射 PNG image，但我找不到有关如何执行此操作的正确示例。从文档here我了解到这段代码应该读取像素/索引：

imtest.cpp：

#include <iostream>

#include <Magick++.h>

int main(int argc, const char *argv[])
{
    std::cout << "Reading " << argv[1];
    Magick::Image img;
    try
    {
        img.read(argv[1]);
    }
    catch (const Magick::Exception &ex)
    {
        throw std::runtime_error("Failed to read image");
    }
    auto imgSize = img.size();
    std::cout << " -> " << imgSize.width() << "x" << imgSize.height() << ", ";
    if (img.classType() == Magick::ClassType::PseudoClass && img.type() == Magick::ImageType::PaletteType)
    {
        std::vector<uint8_t> data;
        std::cout << "paletted, " << img.colorMapSize() << " colors" << std::endl;
        // get palette indices as unsigned chars
        const auto nrOfColors = img.colorMapSize();
        // auto pixels = img.getConstPixels(0, 0, img.columns(), img.rows()); // needed to call this first for getConstMetacontent to work?
        auto indices = static_cast<const uint8_t *>(img.getConstMetacontent());
        const auto nrOfIndices = img.columns() * img.rows();
        for (std::remove_const<decltype(nrOfIndices)>::type i = 0; i < nrOfIndices; i++)
        {
            data.push_back(indices[i]);
        }
        std::cout << "Read " << data.size() << " pixels" << std::endl;
    }
    else
    {
        throw std::runtime_error("Unsupported image format");
    }
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.16)

find_package(PkgConfig REQUIRED)

pkg_check_modules(LIBMAGICK REQUIRED IMPORTED_TARGET
    Magick++
)

add_definitions(-DMAGICKCORE_HDRI_ENABLE=0)
add_definitions(-DMAGICKCORE_QUANTUM_DEPTH=16)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_C_STANDARD 11)

add_executable(imtest imtest.cpp)
target_include_directories(imtest PRIVATE ${ImageMagick_INCLUDE_DIRS})
target_link_libraries(imtest PkgConfig::LIBMAGICK)

与

imtest <image>

一起跑步

这是正确的，还是我做错了什么？ getConstMetacontent() 中有一个 bug 最近已修复，但我仍然不知道我所做的是否正确。
在 ImageMagick 6 / Magick++ 中，获取索引像素数据的函数称为 getConstIndexes()，但它不再存在。

Answer 1

使用Magick++读取IndexChannel的正确代码是：

#include <iostream>
#include <Magick++.h>

int main(int argc, const char *argv[])
{
    std::cout << "Reading " << argv[4];
    Magick::Image img;
    try
    {
        img.read(argv[4]);
    }
    catch (const Magick::Exception &ex)
    {
        throw std::runtime_error("Failed to read image");
    }
    auto imgSize = img.size();
    std::cout << " -> " << imgSize.width() << "x" << imgSize.height() << ", ";
    if (img.classType() == Magick::ClassType::PseudoClass && img.type() == Magick::ImageType::PaletteType)
    {
        std::vector<MagickCore::Quantum> data;
        std::cout << "paletted, " << img.colorMapSize() << " colors" << std::endl;
        img.channel(MagickCore::IndexChannel);
        auto pixels = img.getConstPixels(0, 0, img.columns(), img.rows());
        for (std::size_t i = 0; i < img.columns() * img.rows(); i++)
        {
            auto value = *pixels++;
            std::cout << value << ", ";
            data.push_back(value);
        }
        std::cout << "Read " << data.size() << " pixels" << std::endl;
    }
    else
    {
        throw std::runtime_error("Unsupported image format");
    }
}