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Updated 2 years 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.

show me…


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": "https://s3.amazonaws.com/bltemp/boys640.jpg",
"pre_process": [{
"job": {
"src": "https://s3.amazonaws.com/img.blitline/mask3.png",
"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": "http://www.scala-lang.org/docu/files/ScalaByExample.pdf",
"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" : "https://s3.amazonaws.com/blitdoc/pngs/boys_subimage.jpg"

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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