feat(fits): add FITS image support

.gitmodules

@@ -110,3 +110,6 @@
 	path = dependencies/small_vector
 	url = https://github.com/gharveymn/small_vector
 	shallow = true
+[submodule "dependencies/tinyfits"]
+	path = dependencies/tinyfits
+	url = https://github.com/cek/tinyfits.git

CMakeLists.txt

@@ -152,6 +152,7 @@ set(TEV_SOURCES
     include/tev/imageio/Exif.h src/imageio/Exif.cpp
     include/tev/imageio/ExrImageLoader.h src/imageio/ExrImageLoader.cpp
     include/tev/imageio/ExrImageSaver.h src/imageio/ExrImageSaver.cpp
+    include/tev/imageio/FitsImageLoader.h src/imageio/FitsImageLoader.cpp
     include/tev/imageio/GainMap.h src/imageio/GainMap.cpp
     include/tev/imageio/IcoImageLoader.h src/imageio/IcoImageLoader.cpp
     include/tev/imageio/ImageLoader.h src/imageio/ImageLoader.cpp

README.md

@@ -130,6 +130,7 @@ $ cpack --config build/CPackConfig.cmake
 ## File Formats
 
 - __EXR__ (via [OpenEXR](https://github.com/AcademySoftwareFoundation/openexr))
+- __FITS__ (via [tinyfits](https://github.com/cek/tinyfits))
 - __JPEG XL__ (including gain maps; via [libjxl](https://github.com/libjxl/libjxl))
 - __JPEG__ (including gain maps, e.g. HDR pictures from Android; via [libjpeg-turbo](https://github.com/libjpeg-turbo/libjpeg-turbo))
 - __JPEG 2000__ (via [openjpeg](https://github.com/uclouvain/openjpeg))

include/tev/imageio/FitsImageLoader.h

@@ -0,0 +1,37 @@
+/*
+ * tev -- the EDR viewer
+ *
+ * Copyright (C) 2026 Thomas Müller <contact@tom94.net>
+ *
+ * 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 3 of the License.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <tev/Image.h>
+#include <tev/imageio/ImageLoader.h>
+
+#include <istream>
+
+namespace tev {
+
+class FitsImageLoader final : public ImageLoader {
+public:
+    Task<std::vector<ImageData>> load(
+        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+    ) const override;
+
+    std::string name() const override { return "FITS"; }
+};
+
+} // namespace tev

src/HelpWindow.cpp

@@ -264,6 +264,7 @@ HelpWindow::HelpWindow(Widget* parent, weak_ptr<Ipc> weakIpc, function<void()> c
     addLibrary(about, "qoi", "QOI image format library");
     addLibrary(about, "small_vector", "Vector with small buffer optimization");
     addLibrary(about, "stb_image(_write)", "Single-header library for loading and writing images");
+    addLibrary(about, "tinyfits", "Single-header FITS image format library");
     addLibrary(about, "tinylogger", "Minimal pretty-logging library");
     addLibrary(about, "UTF8-CPP", "Lightweight UTF-8 string manipulation library");
     addLibrary(about, "XMP-Toolkit-SDK", "XMP metadata parsing library");

src/imageio/FitsImageLoader.cpp

@@ -0,0 +1,116 @@
+/*
+ * tev -- the EDR viewer
+ *
+ * Copyright (C) 2026 Thomas Müller <contact@tom94.net>
+ *
+ * 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 3 of the License.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <tev/imageio/FitsImageLoader.h>
+
+#define TINYFITS_IMPLEMENTATION
+#include <tinyfits/tinyfits.h>
+
+using namespace nanogui;
+using namespace std;
+
+namespace tev {
+
+Task<vector<ImageData>> FitsImageLoader::load(istream& iStream, const fs::path&, string_view, const ImageLoaderSettings&, int priority) const {
+    char magic[9];
+    iStream.read(magic, 9);
+
+    if (string_view{magic, 9} != "SIMPLE  =") {
+        throw FormatNotSupported{"Not a FITS file."};
+    }
+
+    iStream.clear();
+    iStream.seekg(0, iStream.end);
+    const auto dataSize = iStream.tellg();
+    iStream.seekg(0, iStream.beg);
+
+    HeapArray<char> data(dataSize);
+    iStream.read(data.data(), dataSize);
+
+    TinyFits fits = {};
+    void* pixels = nullptr;
+    int err = tinyfits_load_from_memory(&fits, data.data(), (size_t)dataSize, &pixels);
+    if (err != TINYFITS_OK) {
+        tinyfits_free(&fits);
+        throw ImageLoadError{fmt::format("Failed to load FITS: {}", tinyfits_error_string(err))};
+    }
+
+    const Vector2i size{fits.width, fits.height};
+    const auto numPixels = (size_t)fits.width * (size_t)fits.height;
+    if (numPixels == 0) {
+        tinyfits_free_buffer(pixels);
+        tinyfits_free(&fits);
+        throw ImageLoadError{"Image has zero pixels."};
+    }
+
+    const auto numChannels = (size_t)fits.num_channels;
+
+    // Convert native pixel data to normalized float32 for display.
+    // tinyfits_to_float normalizes unsigned integer types to [0,1]; floats pass through as-is.
+    const auto totalSamples = numPixels * numChannels;
+    vector<float> floatPixels(totalSamples);
+    err = tinyfits_to_float(&fits, pixels, floatPixels.data());
+    tinyfits_free_buffer(pixels);
+    if (err != TINYFITS_OK) {
+        tinyfits_free(&fits);
+        throw ImageLoadError{fmt::format("Failed to convert FITS pixels to float: {}", tinyfits_error_string(err))};
+    }
+
+    vector<ImageData> result(1);
+    ImageData& resultData = result.front();
+
+    for (size_t c = 0; c < numChannels; ++c) {
+        static const string rgbNames[] = {"R", "G", "B"};
+        string name;
+        if (numChannels == 1) {
+            name = "L";
+        } else if (numChannels == 3) {
+            name = rgbNames[c];
+        } else {
+            name = to_string(c);
+        }
+        resultData.channels.emplace_back(name, size, EPixelFormat::F32, EPixelFormat::F32);
+    }
+
+    // tinyfits_to_float returns planar data (all of channel 0, then channel 1, ...)
+    for (size_t c = 0; c < numChannels; ++c) {
+        auto view = resultData.channels[c].view<float>();
+        memcpy(view.data(), floatPixels.data() + c * numPixels, numPixels * sizeof(float));
+    }
+
+    resultData.hasPremultipliedAlpha = false;
+    resultData.nativeMetadata.transfer = ituth273::ETransfer::Linear;
+
+    AttributeNode root;
+    root.name = "FITS header";
+    AttributeNode& section = root.children.emplace_back();
+    section.name = "";
+    for (int i = 0; i < fits.num_keywords; ++i) {
+        AttributeNode node;
+        node.name = fits.keywords[i].key;
+        node.value = fits.keywords[i].value;
+        section.children.push_back(std::move(node));
+    }
+    resultData.attributes.push_back(std::move(root));
+
+    tinyfits_free(&fits);
+
+    co_return result;
+}
+
+} // namespace tev

src/imageio/ImageLoader.cpp

@@ -20,6 +20,7 @@
 #include <tev/imageio/ClipboardImageLoader.h>
 #include <tev/imageio/EmptyImageLoader.h>
 #include <tev/imageio/ExrImageLoader.h>
+#include <tev/imageio/FitsImageLoader.h>
 #include <tev/imageio/IcoImageLoader.h>
 #include <tev/imageio/ImageLoader.h>
 #include <tev/imageio/Jpeg2000ImageLoader.h>
@@ -65,6 +66,7 @@ const vector<unique_ptr<ImageLoader>>& ImageLoader::getLoaders() {
 #ifdef TEV_SUPPORT_JXL
         imageLoaders.emplace_back(new JxlImageLoader());
 #endif
+        imageLoaders.emplace_back(new FitsImageLoader());
         imageLoaders.emplace_back(new QoiImageLoader());
         imageLoaders.emplace_back(new WebpImageLoader());
         imageLoaders.emplace_back(new Jpeg2000ImageLoader());
@@ -89,6 +91,7 @@ const vector<string_view>& ImageLoader::supportedMimeTypes() {
 #endif
         "image/apng",
         "image/bmp",
+        "image/fits",
         "image/gif",
 #ifdef TEV_SUPPORT_HEIC
         "image/heic",