Last updated: December 19, 2024
# Exploring the 'output\_meta' parameter in Transloadit
**Samuel Ogundipe**
Technical Writer · Lagos, Nigeria · Show bio
[](https://github.com/samuelayo)
If you have ever come across the documentation for the[/upload/handle](/docs/robots/upload-handle.md) and[/image/resize](/docs/robots/image-resize.md) Robots, you may have seen the`output_meta` parameter. You may then also have wondered what exactly it does. After all, unlike with most other parameters, its use might not be immediately clear from the name alone :)
So, why not take a moment to explain how this parameter works, and why it was created!
## The output\_meta parameter
The idea behind the `output_meta` parameter is to give our customers the ability to collect certain metadata about their files. Sounds nice to have on all the time, right? Well, it is also a lot more taxing on CPU power to calculate. So, in order to keep those Assemblies running fast all the time, we made a parameter for the collection of some metadata and kept it disabled by default.
You can define the `output_meta` parameter on our Robots' Steps in order to choose whether you want extra metadata per encoding result. While this gives our users the luxury of fine control and granularity, it also led to a problem: how do you enable it for uploaded files? We have supported file uploads since 2008, but they have always been a bit of an odd duck, because uploads used to be the only files that weren't the result of our Robots.
So, after the introduction of fine-grained control through the `output_meta` parameter, the next logical step was to encapsulate upload handling in a Robot of its own and launch the[/upload/handle](/docs/robots/upload-handle.md) Robot alongside the new parameter. Now there are no more exceptions, and behavior can be modified at every Step for every file.
## How does it work?
The `output_meta` parameter accepts an object. For now, however, we only have the boolean property`has_transparency` available. If this property is set to `true`, it analyzes the image and tells you if it has transparent parts. Since calculating `has_transparency` can take a long time for certain files, we have it excluded from the result set by default. After all, we don't want to have our customers paying a premium in execution time if they don't even care about this property in the first place.
If you do want to know whether, for instance, your uploaded files have transparent areas, you can set `"output_meta": { "has_transparency": true }` on the[/upload/handle](/docs/robots/upload-handle.md) Robot, after which you'll find`meta.has_transparency` set on the resulting files.
Let's take a look at how to build an Assembly that uses this parameter. Feel free to follow along!
## Creating the Assembly
In this section, we will be creating two separate Assembly Instructions, which will show us how the parameter is used in both the [/upload/handle](/docs/robots/upload-handle.md) Robot and the [/image/resize](/docs/robots/image-resize.md) Robot.
```json
{
"steps": {
":original": {
"robot": "/upload/handle",
"output_meta": {
"has_transparency": true
}
}
}
}
```
```json
{
"steps": {
":original": {
"robot": "/upload/handle"
},
"resized": {
"use": [":original"],
"robot": "/image/resize",
"result": true,
"background": "white",
"flatten": false,
"height": 500,
"imagemagick_stack": "v2.0.3",
"resize_strategy": "pad",
"rotation": false,
"strip": true,
"trim_whitespace": true,
"width": 250,
"output_meta": {
"has_transparency": true
}
}
}
}
```
Here, we have two different sets of Assembly Instructions. One using only the[/upload/handle](/docs/robots/upload-handle.md) Robot and the other using the[/image/resize](/docs/robots/image-resize.md) Robot.
Notice that in the Assembly Instructions that feature the[/image/resize](/docs/robots/image-resize.md) Robot, the `output_meta` property does not appear in the `:original` step, but in the `resized` step. This is because in theseAssembly Instructions, we are testing for transparency when the file is being resized and not when it is uploaded.
## The results
After running any of the above Assembly Instruction sets, we can see from the JSON result for the [/upload/handle](/docs/robots/upload-handle.md) Robot that the `meta`property of the `uploads` key has a field called `has_transparency`, which is set to `true`. This property only returns `true` if the image has transparent parts.
Likewise, for the JSON result returned for the [/image/resize](/docs/robots/image-resize.md) Robot, the `meta` property of the `resized` key under the `results` section has a field called `has_transparency`, which is set to `true`.
As you can see, the `output_meta` parameter can be quite handy! We're also considering to let you opt out of other existing meta keys in order to speed up Assemblies. For instance, we're currently calculating MD5 hashes for all files by default, even though many use cases may not need that. So, as soon as we have more properties that can be specified with this parameter, we'll be sure to let you know! 💖
[#integrations](/blog/tags/integrations.md)[#image-resize-robot](/blog/tags/image-resize-robot.md)[#upload-handle-robot](/blog/tags/upload-handle-robot.md)
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