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Updated 7 months ago ​by Blitline Support


Some jobs and workflows do not fit in to the linear, asynchronous flow of a Blitline job. To help accommodate these we have added a “pre_process” tag which allows you to define functionality that can happen “before” the Blitline job is executed. This “pre_process” tag can contain any of the following “functions” formatted in the standard Blitline syntax.


Before processing a job, Blitline can move the original “src” file to a particular S3 destination.

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We have had a bunch of feedback regarding the ability to process an image and then use that image IN a different Blitline job. Usually this occurs when compositing images, and you want to resize image “A” and the composite it on to a resized image “B”. With the current implementation, this takes 2 separate Blitline jobs. By having jobs in a “pre_process” tag, you can assure that 1 job is done before executing another job, thus providing a “synchronous” queue of image processing.

In other words… pre_processed jobs will be executed BEFORE the main Blitline job. You can also reference those pre_processed images in your main Blitline job.

You can watch a small presentation about this here…

In a nutshell, you can just put a regular “job” inside a “pre_process” tag, this job will be executed before the main Blitline job.

  "application_id": "YOUR_APP_ID",
  "src": "",
  "pre_process": [{
    "job": {
      "src": "",
      "functions": [{
        "name": "resize_to_fit",
        "params": {
          "width": 640
        "save": {
          "image_identifier": "MY_CLIENT_ID"
  "functions": [{
    "name": "composite",
    "params": {
      "gravity": "CenterGravity",
      "src": "&MY_CLIENT_ID",
      "composite_op": "CopyOpacityCompositeOp",
      "as_mask": "true"
    "save": {
      "image_identifier": "output"
Notice, to reference a “pre_process” job output, just place a “&” in fron of the “image_identifier” from the “pre_process” job.


You can use Blitline to ONLY read metadata about a file without actually downloading the whole file or doing any processing on it. This is referred to as “peeking” at an image.

  "application_id": "YOUR_APP_ID",
  "src": "",
  "v": 1.21,
  "pre_process": {
    "peek": true

The resulting postback will contain all the metadata about the file contained in the “src” field.


You can search for an image INSIDE another image. This functionality will take a subimage and search for it inside the jobs primary “src”.

    "src_type" : "pre_process_only",
    "v" : 1.22,
            "find_subimage" : {
                "subimage_src" : ""

In this example, Blitline will look for “boys_subimage.jpg” inside the “boys.jpeg” image. The results will look like:

  "action_result": {
    "is_found": true,
    "found_location": {
      "x": 100,
      "y": 100,
      "accuracy": 0.8258131

Where accuracy represents how certain we are about the image being found in that particular location.

NOTE: It will only return 1 result, the one with the highest accuracy.

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