Optimize documents

Usage example

{
  "steps": {
    "optimized": {
      "robot": "/document/optimize",
      "use": ":original",
      "preset": "ebook"
    }
  }
}

Parameters

• interpolate

  boolean | Record<string, boolean>

• output_meta

  Record<string, boolean> | boolean | Array<string>

• result

  boolean (default: false)

• queue

  batch

• force_accept

  boolean (default: false)

• ignore_errors

  boolean | Array<meta | execute> (default: [])

• use

  string | Array<string> | Array<object> | object

• preset

  screen | ebook | printer | prepress (default: "ebook")

• image_dpi

  string | number

• compress_fonts

  boolean (default: true)

• subset_fonts

  boolean (default: true)

• remove_metadata

  boolean (default: false)

• linearize

  boolean (default: true)

• compatibility

  1.4 | 1.5 | 1.6 | 1.7 | 2.0 (default: "1.7")

Demos

This Robot reduces PDF file sizes. It recompresses images, subsets fonts, and applies various optimizations to reduce file size while maintaining acceptable quality.

Quality Presets

The Robot supports four quality presets that control the trade-off between file size and quality:

Optimize PDF file size.

Controls whether Assembly Variables are interpolated for individual instruction fields.

By default, most Robot instruction fields interpolate Assembly Variables. Set this to false to treat every instruction field as literal text, or set an individual field path to false to treat only that field as literal text. For Robot-specific fields that are literal by default, set this to true or set that field path to true to opt back into interpolation.

Use field names such as path, or dotted paths such as ffmpeg.vf for nested objects.

Setting the queue to 'batch', manually downgrades the priority of jobs for this step to avoid consuming Priority job slots for jobs that don't need zero queue waiting times

Whether the results of this Step should be present in the Assembly Status JSON

Force a Robot to accept a file type it would have ignored.

By default, Robots ignore files they are not familiar with. 🤖/video/encode, for example, will happily ignore input images.

With the force_accept parameter set to true, you can force Robots to accept all files thrown at them. This will typically lead to errors and should only be used for debugging or combatting edge cases.

Ignore errors during specific phases of processing.

Setting this to ["meta"] will cause the Robot to ignore errors during metadata extraction.

Setting this to ["execute"] will cause the Robot to ignore errors during the main execution phase.

Setting this to true is equivalent to ["meta", "execute"] and will ignore errors in both phases.

Specifies which Step(s) to use as input.

• You can pick any names for Steps except ":original" (reserved for user uploads handled by Transloadit)
• You can provide several Steps as input with arrays:
  

  {
    "use": [
      ":original",
      "encoded",
      "resized"
    ]
  }
  

• You can also tag input Steps with as to pass semantic intent to robots:
  

  {
    "use": [
      {
        "name": ":original",
        "as": "image"
      },
      {
        "name": ":original",
        "as": "mask"
      }
    ]
  }
  

The quality preset to use for optimization. Each preset provides a different balance between file size and quality:

• screen - Lowest quality, smallest file size. Best for screen viewing only. Images are downsampled to 72 DPI.
• ebook - Good balance of quality and size. Suitable for most purposes. Images are downsampled to 150 DPI.
• printer - High quality suitable for printing. Images are kept at 300 DPI.
• prepress - Highest quality for professional printing. Minimal compression applied.

Target DPI (dots per inch) for embedded images. When specified, this overrides the DPI setting from the preset.

Higher DPI values result in better image quality but larger file sizes. Lower values produce smaller files but may result in pixelated images when printed.

Common values:

• 72 - Screen viewing
• 150 - eBooks and general documents
• 300 - Print quality
• 600 - High-quality print

Whether to compress embedded fonts. When enabled, fonts are compressed to reduce file size.

Whether to subset embedded fonts, keeping only the glyphs that are actually used in the document. This can significantly reduce file size for documents that only use a small portion of a font's character set.

Whether to strip document metadata (title, author, keywords, etc.) from the PDF. This can provide a small reduction in file size and may be useful for privacy.

Whether to linearize (optimize for Fast Web View) the output PDF. Linearized PDFs can begin displaying in a browser before they are fully downloaded, improving the user experience for web delivery.

The PDF version compatibility level. Lower versions have broader compatibility but fewer features. Higher versions support more advanced features but may not open in older PDF readers.

• 1.4 - Acrobat 5 compatibility, most widely supported
• 1.5 - Acrobat 6 compatibility
• 1.6 - Acrobat 7 compatibility
• 1.7 - Acrobat 8+ compatibility (default)
• 2.0 - PDF 2.0 standard

Allows you to specify a set of metadata that is more expensive on CPU power to calculate, and thus is disabled by default to keep your Assemblies processing fast.

For images, you can add "has_transparency": true in this object to extract if the image contains transparent parts and "dominant_colors": true to extract an array of hexadecimal color codes from the image.

For images, you can also add "blurhash": true to extract a BlurHash string — a compact representation of a placeholder for the image, useful for showing a blurred preview while the full image loads.

For videos, you can add the "colorspace: true" parameter to extract the colorspace of the output video.

For videos, you can also add "interlaced": true to detect whether the video is interlaced. This combines the cheap ffprobe field_order flag with a bounded idet sampling pass over the first frames of the source, exposing interlaced, field_order, and a diagnostic interlace_detection object under file.meta. This is computationally expensive and billed accordingly.

For audio, you can add "mean_volume": true to get a single value representing the mean average volume of the audio file.

You can also set this to false to skip metadata extraction and speed up transcoding.