Help & Documentation

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FastCompressor is a desktop application for compressing images quickly and efficiently — right on your machine, with no uploads to any server.

Installation

1. Download FastCompressor from fastcompressor.com
2. macOS — Open the .dmg file, drag FastCompressor to your Applications folder
3. Windows — Run the installer .exe and follow the prompts
4. Linux — Use the .AppImage, .deb, or .rpm package for your distro

Your First Compression

1. Launch FastCompressor
2. Drag and drop images onto the upload area (or click to browse)
3. Adjust quality and settings in the right panel
4. Click Compress in the bottom action bar
5. Download or save your compressed files

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Step 1 — Add Files Drag and drop your images into the upload area, or click the area to open a file picker. Supported input formats: JPEG, PNG, WebP, TIFF, BMP, GIF.

Step 2 — Configure Settings Use the Compression Settings panel on the right to choose:

• Compression mode (Lossy or Lossless)
• Quality level (30–100%)
• Output format (JPEG, PNG, WebP, or Keep Original)
• Resize dimensions
• Custom filename rules
• Metadata handling

Step 3 — Compress Click the Compress button in the action bar at the bottom. FastCompressor processes files locally — nothing leaves your machine.

Step 4 — Review & Save After compression, you'll see a results page showing:

• Original vs compressed file sizes
• Percentage saved per file
• Total space saved
• Processing time

Click Download All to save, or Compress More to start again.

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Compression Mode

Quality Slider (30–100%)

Only Convert if Smaller

Enable this checkbox to skip conversion when the output would be larger than the input. This is especially useful when batch-converting mixed formats — it prevents photos from getting bigger when converted to PNG.

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Resize your images during compression by specifying target dimensions in the settings panel.

• Width / Height — Enter pixel values. Leave one field blank to auto-calculate from the other using the aspect ratio.
• Maintain Aspect Ratio — When enabled, changing width auto-adjusts height (and vice versa) to prevent stretching or distortion.

Common Resize Presets:

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By default, compressed files are saved alongside the originals. You can choose a custom output folder:

1. Click Select next to the Output Folder option in the Compression Settings panel
2. Choose any folder on your computer
3. All compressed files will be saved there

You can also set a default output folder in Settings that persists across all sessions, so you don't have to pick a folder each time.

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Customize how compressed files are named to keep your files organized:

• Prefix — Add text before the original filename (e.g., compressed_photo.jpg)
• Suffix — Add text after the filename (e.g., photo_small.jpg)
• Custom naming pattern — Define your own naming convention

This helps you keep compressed files organized alongside the originals without manually renaming each one.

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Images often contain hidden metadata (EXIF) — camera model, GPS location, date taken, shutter speed, and more.

FastCompressor gives you control over this data:

• Preserve Metadata — Keep all original EXIF data in the compressed output
• Strip Metadata — Remove all metadata for smaller files and better privacy

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Presets let you save and reuse compression configurations with one click — no need to manually adjust settings every time.

Built-in Presets:

Custom Presets: Create your own presets in Settings → Presets → Add Custom Preset. Configure the format, quality, resize, and mode, give it a name, and it's saved locally for future use.

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After compression completes, you'll see a detailed results page:

• Per-file breakdown — Original size → compressed size, and percentage saved for each file
• Total summary — Aggregate stats across all files in the batch
• Processing time — How long the compression took
• Success / failure indicators — Green dot for successful, red for errors with details

From the results page you can:

• Download All — Save all compressed files at once
• Compress More — Return to the upload screen to start a fresh batch

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Logged-in users get a Profile page that tracks all compression activity over time.

Your Dashboard Shows:

• Total files compressed (all-time)
• Total original size vs compressed size
• Total space saved (with percentage)
• Average compression ratio
• Average processing time per file
• Most used output format
• Largest file ever compressed
• Monthly compression stats (batches and files this month)

Batch History: Every compression session is saved as a "batch." You can expand any batch to see:

• Individual file details (name, original → compressed size)
• Per-file compression percentage
• Success or failure status with error messages
• Processing time per batch
• The plan used for that batch

Use Expand All / Collapse All to quickly browse your history.

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Access Settings from the user menu in the top-right corner. Available options:

Theme Switch between Light, Dark, and Auto (follows system preference).

Default Output Folder Set a folder that's used by default for all compressions, so you don't have to select one each time.

Default Compression Level Set your preferred compression mode (Lossy/Lossless) and quality level as the default for new sessions.

Notifications Enable or disable desktop notifications when compression completes.

Advanced Options Fine-tune performance settings:

• Parallel Compression — Number of files processed simultaneously (1–16)
• Chunk Size — Processing chunk size in MB
• Max File Size — Maximum allowed file size in MB
• Timeout — Maximum time allowed per file in seconds

Reset All Settings Clears all app data, history, and preferences back to defaults.

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Power User Tips:

• Drop entire folders to compress all images inside at once
• Use WebP for the smallest possible file sizes — it outperforms JPEG and PNG in most cases
• 70% quality is the sweet spot — visually indistinguishable from 100% for most photos
• Enable "Only convert if smaller" when batch-converting mixed formats to prevent PNG bloat
• Set a default output folder in Settings to skip the save dialog every time
• Create custom presets for your most common workflows (e.g., "Blog images", "Client deliverables")
• Check your Profile to track how much storage you've saved over time

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"Offline Mode" banner appears FastCompressor needs internet to verify your login session. Your files are still processed locally, but some account features may be unavailable. Reconnect to the internet and restart the app to restore full functionality.

Compression makes the file larger This happens when converting photos to PNG (a lossless format). Switch to JPEG or WebP for photos. You can also enable "Only convert if smaller" to prevent this automatically.

App won't start / crashes on launch

• macOS: Make sure you dragged the app to Applications. If macOS blocks it, right-click → Open.
• Windows: Try running as Administrator. Check if your antivirus is blocking it.
• Linux: Make the AppImage executable: chmod +x FastCompressor-*.AppImage

Compression is slow

• Large files (10MB+) naturally take longer.
• FastCompressor processes multiple files in parallel — close other heavy apps to free up CPU and RAM.
• You can adjust the parallel compression setting in Settings → Advanced Options.

Files are not saving

• Make sure you have write permission to the output folder.
• Try selecting a different output folder.

"Daily compressions exhausted" Your account has reached the daily compression limit. This resets automatically. Upgrade your plan for unlimited compressions.

Can't log in

• Check your internet connection.
• Make sure you're using the same email you registered with.
• Try closing and reopening the app.

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Q: Are my images uploaded to a server? No. FastCompressor processes everything locally on your machine. Your files never leave your computer.

Q: What image formats are supported? Input: JPEG, PNG, WebP, TIFF, BMP, GIF. Output: JPEG, PNG, WebP, or Keep Original.

Q: Is there a maximum file size? No hard limit. FastCompressor can handle files of any size, though very large files (50MB+) will take longer to process.

Q: How many files can I compress at once? There is no file count limit per batch. You can drag hundreds of files at once.

Q: Can I use FastCompressor offline? Yes. Compression works fully offline. You only need internet for login verification.

Q: Does it work on Apple Silicon (M1/M2/M3/M4)? Yes. FastCompressor has a native Apple Silicon (arm64) build for maximum performance.

Q: What compression engine does FastCompressor use? FastCompressor uses a highly optimized image processing engine to ensure maximum speed and quality.

Q: Where are compressed files saved? By default, to the same folder as the originals. You can change this in Compression Settings or set a default in Settings.

Q: Will my original files be overwritten? No. Compressed files are always saved as new files — your originals are never modified or deleted.

Q: How do I update the app? FastCompressor checks for updates automatically. You'll see a prompt when a new version is available.

Q: What platforms does FastCompressor support? macOS (Intel & Apple Silicon), Windows (64-bit), and Linux (AppImage, .deb, .rpm).

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• Feature Requests — Submit a feature request
• Bug Reports — Report a bug
• Website — fastcompressor.com