Tutorials in Kotlin programming language

If you want to use rethumb with Kotlin check these tutorials:

Paths in Sources

Our API finally allows paths in sources. As listed by our roadmap our API didn’t allow for paths in the domain or subdomain name of a source.

From now on all these are valid sources:

  • my-site.com
  • username.my-site.com
  • subdomain.my-site.com
  • backoffice.my-site.com
  • (NEW) my-site.com/images/
  • (NEW) username.my-site.com/images/dir2/

This could be very useful for clients with resources on shared domains like S3, where all customers might share the same domain or subdomain.

Bring your Custom Domain Name

Starting today you can use your own domain name with rethumb.

By using CNAME records it is possible to point any subdomain to our server.

  1. Choose a subdomain: something like images.yoursite.com.

  2. Create a CNAME record with name=images.yoursite.com and value=domains.rethumb.com within your DNS managament service.

  3. Login into our dashboard at https://dashboard.rethumb.com and create a CNAME record with your subdomain name (images.yoursite.com).

  4. Wait for your DNS changes to propagate and our servers to update.

After these steps you can start using rethumb with your own domain, example:


That will work in the same way as:


More information: CNAMEs – how do they work?

Cover Resize Tutorials

Check our cover resize examples. rethumb can resize an image to cover any dimensions:

Cover resize now Available

Our new operation cover is now available. This feature allows you to resize an image to any dimension: upscaling, downscaling and cropping as needed.

An example, if you have an image with dimensions 300 x 300 px you can use the following request to get a new 150 x 200 px image:


Original image

As you can see the new image itseft have no distortion in any way:

Transformed image

This feature is very similiar to CSS background cover, you can read more about it here: CSS3 background-size Property.

Check our API for more details on how to use this new transformation.

WebP Support now Available

Support for WebP images in now available. You can use rethumb to convert WebP images to other formats like JPG or PNG and vice-versa.

Convert from WebP to JPG:


Convert from JPG to WebP:


Format Conversion Tutorials

Check our format conversion examples. rethumb can convert to and from JPG, GIF, PNG, TIFF and WebP:

Format Conversion now Available

Starting today our format conversion feature is available for all our customers.

This feature allows you to convert from an image file format to another. At the moment we can convert from and to JPG, GIF, PNG, TIFF and WebP.

The following example will convert a JPG image to GIF, PNG and WebP. Note that the format feature must be used with other transformation operation like height, square or width.


Documention on this feature is online at http://rethumb.com/api.

It is a paid feature so you’ll need to subscribe to a paid plan. Check our prices at http://rethumb.com/pricing.

Any question contact us at [email protected].

WebP Support

rethumb will start supporting WebP images soon. WebP is the Google image format for the web.

From their site:

“WebP is a new image format that provides lossless and lossy compression for images on the web. WebP lossless images are 26% smaller in size compared to PNGs. WebP lossy images are 25-34% smaller in size compared to JPEG images”

You can read more about it at https://developers.google.com/speed/webp/?hl=en

Not many browsers support this tecnology: http://caniuse.com/#search=webp. Be careful when sending WebP images to your clients.

Format Conversion

We are preparing a new feature for rethumb: format conversion.

At the moment our API creates images with the same image format as the input.
E.G.: PNG images are converted to PNG thumbnails, etc.

This new feature will allow our users to select the output format.
In that way it’ll be possible to convert PNG images to JPG thumbnails, etc.

Our API will support conversion from PNG, JPG, GIF, TIFF and WEBP to PNG, JPG, GIF, TIFF and WEBP.