How to render a source image through rokka into your desired format

Table of Contents

Render an image through a stack

The recommended way to render images is through stacks. Using a stack, the rendering instructions are stored centrally and the result can be cached. For hash you can use either the full hash or the short_hash returned by the API.

curl -X GET 'https://{organization}{stack-name}/{hash}.{format}'

Note: Additional text after the hash is ignored. You can use this for example to add a slug to the image URL for SEO purposes. This slug can contain all characters except a /.

curl -X GET 'https://{organization}{stack-name}/{hash}/{slug}.{format}'

Overwriting stack operation options

If you want to overwrite some stack operation options within the URL, you can do that. For example, if you want to have different resize width, but leave the rest as is. It's the same format as mentioned below for dynamically rendering an image. You can also add/overwrite stack options.


See also the stack variables chapter for another way to overwrite stack operation options.

Dynamically render an image

You can use the dynamic renderer to specify operations directly in the URL without the need for stacks:


URL Operations are concatenated with double hyphens (--). For example, to do a resize and then a rotate operation, the URL would look like this:


You can also add stack options do a dynamic stack, prefix them with options-, eg:


We recommend using stacks instead of the dynamic renderer for a better reusability of your rendered images.

See operations for the definition of URL operations.

Rendering animated GIFs

rokka can also render and output animated GIFs in different formats, like animated WebP, MP4 and WebM. And can do all the stack operations you can use on a still image. It also automatically delivers in the usually much smaller WebP format instead of GIF, if you set autoformat to true on the stack. Additionally it optimizes the original GIF to make it as small as possible in the asynchronous optimization step. The gif.quality stack options defines, how much it should be compressed in this phase. Default is 60, 100 means lossless compression, minimum is 1.

Currently, only animated GIFs are supported as source image. Animated WebP or even videos are not, those are only supported on the output side. We may add that, if there's demand.

If you just want to return the original animated gif in an optimized format to save bandwidth, create a stack without operations and set autoformat to true.

    "stack_operations": [],
    "stack_options": {
        "autoformat": true

The following stack definition would for example add a watermark to your gif and resize it to a width of 300

    "stack_operations": [
            "name": "composition",
            "options": {
                "mode": "background",
                "secondary_image": "0dee47",
                "anchor": "right_bottom"
            "name": "resize",
            "options": {
                "width": 300
    "stack_options": {
        "autoformat": true

Be aware, that the transformation - especially with stack operations on large gifs - will take quite some time on the first hit and you may run into time-outs. If that's an issue for you, please report, and we will see, if we can increase some limitations for you.

Output as video

To save even more bandwidth, it's advised to display the animations as video, instead of as a GIF. They will be much smaller. You have to use the <video> on your HTML tag to do this. Eg.

<video autoplay loop muted playsinline poster="">
    <source src="" type="video/webm">
    <source src="" type="video/mp4">

Getting a blurhash from a rendered image

BlurHash is a compact representation of a placeholder for an image. With this short hash you can display "blurry" placeholders in a webpage before the actual image is loaded. See for more details about this technique.

Rokka can provide this short hash to you, directly for each rendered image, so you don't have to build/compute that by yourself. Use the blur "format", eg, make a GET request to this and you'll get the blurhash back. This hash you can then store in your database or similar (along with the rokka hash for example) and later use it for the blurhash library.

The result looks like this:

for this image

The code for this example using blurhash-img is:

<script type="module" src=""></script>
  style="--aspect-ratio: 840/1260; width: 50%">

Rendering images from a remote URL

See the Loading images from a remote URL chapter for more details about that.

Use another organization as fallback for rendering images

Sometimes you have different rokka organizations for test/stage and production environments, but need the same images in both of them. You can easily copy all images from one org to another, but this is a long and resource intensive process, when you have many images.

Another approach, if you only need all the images for rendering and not via API operations, you can set the render_org_fallback organization option to another organisation. With this setting, whenever an image is not found for rendering in the original organization, rokka checks the fallback organisation and loads it from there, if available.

As said, they don't show up in the API, for example the image search. So if your CMS does interact with rokka to read from those images, you won't get them. But you can still upload or copy the same images later, if you need to. Also, you still have to copy the stacks from one organization to the other, there's no fallback for them.

To actually be able to link two organizations with this, you need to be admin on both organizations.

curl -H 'Content-Type: application/json' -X PUT '' -d '{"render_org_fallback": "$FALLBACK_ORG"}'

Signed URLs for limited access

rokka has the possibility to let you sign render URLs, so that those URLs are only valid for a certain time or can only be accessed from certain IP ranges. If you need that feature, get in contact with us.