Extract thumbnail images from documents

🤖/document/thumbs generates an image for each page in a PDF file or an animated GIF file that loops through all pages.

Usage example

{
  "steps": {
    "thumbnailed": {
      "use": ":original",
      "robot": "/document/thumbs",
      "width": 200,
      "resize_strategy": "fit",
      "trim_whitespace": false
    }
  }
}

Parameters

• interpolate

  boolean | Record<string, boolean>

  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.

• output_meta

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

  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.

• result

  boolean(default: false)

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

• queue

  batch

  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

• force_accept

  boolean(default: false)

  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

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

  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.

• use

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

  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"
        }
      ]
    }
    

  Tip

  That's likely all you need to know about use, but you can view Advanced use cases.

• page

  string | number | null(default: null)

  The PDF page that you want to convert to an image. By default the value is null which means that all pages will be converted into images.

• page_range

  string | null(default: null)

  A page range to extract, in the format "start-end" (e.g., "1-20"). Extraction starts from the first page in the range and proceeds sequentially, stopping gracefully when a page does not exist. This is useful for PDFs where the total page count cannot be determined.

  This parameter cannot be used together with page, and is not supported with GIF format. When page_range is set, the robot does not need to know the total page count upfront, making it robust for PDFs that fail page count detection.

• format

  gif | jpeg | jpg | png(default: "png")

  The format of the extracted image(s).

  If you specify the value "gif", then an animated gif cycling through all pages is created. Please check out this demo to learn more about this.

• delay

  string | number

  If your output format is "gif" then this parameter sets the number of 100th seconds to pass before the next frame is shown in the animation. Set this to 100 for example to allow 1 second to pass between the frames of the animated gif.

  If your output format is not "gif", then this parameter does not have any effect.

• stack

  ghostscript | vips | pdfium

  Selects the PDF rendering stack. Defaults to Ghostscript.

  Use "pdfium" for page-specific or single-page high-DPI PDF rasterization when Ghostscript is too slow or exhausts scratch space, for example with high-resolution CAD, blueprint, or layered real-estate PDFs. This stack uses PDFium via the Python pypdfium2 bindings and Pillow for final image encoding.

  Use "vips" only when you explicitly want libvips PDF loading. It is lower-overhead, but PDFium was faster in high-DPI floorplan tests while producing comparable output quality.

  The "pdfium" stack currently supports JPG/PNG output, resize_strategy: "fit", a specific page or single-page PDFs, opaque hexadecimal backgrounds, antialiasing, and pdf_use_cropbox.

  The "vips" stack currently supports JPG/PNG output, resize_strategy: "fit", a specific page or single-page PDFs, and hexadecimal or transparent backgrounds.

• width

  string | number

  Width of the new image, in pixels. If not specified, will default to the width of the input image

• height

  string | number

  Height of the new image, in pixels. If not specified, will default to the height of the input image

• resize_strategy

  crop | fillcrop | fit | min_fit | pad | stretch(default: "pad")

  One of the available resize strategies.

• background

  string(default: "#FFFFFF")

  Either the hexadecimal code or name⁠ of the color used to fill the background (only used for the pad resize strategy).

  By default, the background of transparent images is changed to white. For details about how to preserve transparency across all image types, see this demo.

• alpha

  Remove | Set

  Change how the alpha channel of the resulting image should work. Valid values are "Set" to enable transparency and "Remove" to remove transparency.

  For a list of all valid values please check the ImageMagick documentation here⁠.

• density

  string

  While in-memory quality and file format depth specifies the color resolution, the density of an image is the spatial (space) resolution of the image. That is the density (in pixels per inch) of an image and defines how far apart (or how big) the individual pixels are. It defines the size of the image in real world terms when displayed on devices or printed.

  You can set this value to a specific width or in the format widthxheight.

  If your converted image has a low resolution, please try using the density parameter to resolve that.

• antialiasing

  boolean(default: false)

  Controls whether or not antialiasing is used to remove jagged edges from text or images in a document.

• colorspace

  CMY | CMYK | Gray | HCL | HCLp | HSB | HSI | 28 more ↓

  Sets the image colorspace. For details about the available values, see the ImageMagick documentation⁠.

  Please note that if you were using "RGB", we recommend using "sRGB". ImageMagick might try to find the most efficient colorspace based on the color of an image, and default to e.g. "Gray". To force colors, you might then have to use this parameter.

• trim_whitespace

  boolean(default: true)

  This determines if additional whitespace around the PDF should first be trimmed away before it is converted to an image. If you set this to true only the real PDF page contents will be shown in the image.

  If you need to reflect the PDF's dimensions in your image, it is generally a good idea to set this to false.

• pdf_use_cropbox

  boolean(default: true)

  Some PDF documents lie about their dimensions. For instance they'll say they are landscape, but when opened in decent Desktop readers, it's really in portrait mode. This can happen if the document has a cropbox defined. When this option is enabled (by default), the cropbox is leading in determining the dimensions of the resulting thumbnails.

• turbo

  boolean(default: true)

  Enables high-performance mode for faster document processing.

  When enabled, Turbo Mode provides two key optimizations:

  1. Parallel page extraction: For documents with more than 5 pages, multiple processes run in parallel to extract pages simultaneously. The number of parallel processes scales with the document size (up to 4 processes for documents with 13+ pages).

  2. Distributed resizing: Extracted pages are resized concurrently on multiple machines, providing up to 20 times faster processing for large documents.

  Files are emitted as they become available during processing. If you set this to false, pages are extracted sequentially using a single process, and files are emitted only after all processing is complete.

  Turbo Mode increases pricing in that the input document's file size is added for every extracted page. There are no performance benefits nor increased charges for single-page documents.

Demos

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