Coil Viewer

High-speed fullscreen image browser focused on instant navigation through large folders on Windows with sane usability.

Supported Formats

• PNG (.png)
• JPEG (.jpg, .jpeg, .jpe, .jfif)
• WebP (.webp, requires Windows WebP codec — bundled with modern Windows 10/11)
• GIF (.gif, displayed as the first frame)
• BMP / DIB (.bmp, .dib)
• TIFF (.tiff, .tif)

The viewer relies on Windows Imaging Component. Any additional codecs registered with WIC (e.g. HEIC/HEIF) will also work if you add their extensions to config.json.

Build

• Requires .NET SDK 8.0 or later.
• Restore and build: dotnet build CoilViewer/CoilViewer.csproj
• Optional portable release: dotnet publish CoilViewer/CoilViewer.csproj -c Release -r win-x64 --self-contained false
• The published folder contains CoilViewer.exe. Copy the entire directory to keep the app portable.

Usage

• Launch CoilViewer.exe directly, double-click an image file, or pass a file/folder path: CoilViewer.exe "C:\path\image.png"
• Keyboard:
  • Right, Down, Space: next image
  • Left, Up, Backspace: previous image
  • Home/End: jump to first/last image
  • Ctrl+Shift+Arrow: jump halfway toward start/end of sequence
  • A: archive current image to "old" subfolder (moves file and shows next image instantly)
  • Ctrl+O: open image to load its folder
  • Ctrl+R: reload config.json
  • I: toggle metadata overlay
  • / or ?: show keyboard shortcuts
  • =/-: zoom in/out
  • \: reset zoom
  • F11 or double-click: toggle fullscreen
  • Esc: exit fullscreen or close the app
• Mouse:
  • Scroll wheel to navigate
  • Double-click toggles fullscreen
  • Drag window when not fullscreen
• Drag & drop a file or folder onto the window to switch folders.
• Right-click anywhere to open the "Sort" context menu. Choose field (file name, created date, modified date, size) and direction (ascending/descending). The choice is saved immediately and re-used on next launch.

The viewer preloads adjacent images in the background for instant navigation and caches them in memory. Large folders (5k+ images) are handled without blocking the UI.

Configuration

A config.json file is created next to the executable on first launch:

{
  "PreloadImageCount": 20,
  "BackgroundColor": "#000000",
  "FitMode": "Uniform",
  "ScalingMode": "HighQuality",
  "ShowOverlay": true,
  "LoopAround": true,
  "SortField": "FileName",
  "SortDirection": "Ascending"
}

• PreloadImageCount: number of images to preload on each side of the current image. The cache will hold up to (PreloadImageCount * 2 + 1) images total. Default: 20.
• BackgroundColor: any WPF color string (e.g. #111111, Black).
• FitMode: Uniform, UniformToFill, Fill, or None.
• ScalingMode: HighQuality, Fant, LowQuality, or NearestNeighbor.
• ShowOverlay: toggles filename/resolution HUD.
• LoopAround: wrap navigation at folder ends.
• SortField: FileName, CreationTime, LastWriteTime, or FileSize.
• SortDirection: Ascending or Descending.

Update the file, then press Ctrl+R to reload without restarting. Right-click → Sort also updates these values automatically.

Set as Default Viewer

For a portable setup:

1. Publish or copy the build output to a permanent directory.
2. Right-click a .png (or other image) → Open with → Choose another app.
3. Enable Always use this app, click More apps, then Look for another app on this PC.
4. Browse to CoilViewer.exe and select it.

Windows will then launch Coil Viewer for that extension. Repeat for additional image types if desired.