Optimizing images means making them load faster at a minimum visual quality loss. This mainly includes manipulating image format and quality. A right balance of those helps improving conversions and bounce rates; it positively affects your SEO ranking.



Converts an image to one of the following formats:

  • jpeg — JPEG is a lossy image format (good compression, good for photos). JPEG doesn’t support an alpha channel, hence you can use the setfill operation that sets a background color. All browsers support JPEG.
  • png — PNG is a lossless format (good compression only for graphics) with alpha channel support. Supported by all browsers.
  • webp — WebP is a modern image format that supports alpha channel and lossy compression. The format is good for all kinds of images but supported by a limited number of browsers.
  • auto — the image format used for content delivery is set according to the presence of an alpha channel in your input and capabilities of a client.

Technically, the default behavior of auto is about always trying to deliver WebP images based on checking the Accept header. We do it if a client supports the image/webp MIME-type and you are running the default Uploadcare setup with our storage and the default CDN domain,

PNG image with transparency
400x301 png 116Kb
JPEG image, opaque
400x301 jpeg 16Kb
WEBP image with transparency, 10 times smaller file size than JPG
400x301 webp 15Kb
Transparent, size is equal
to the opaque one.

Beside using -/format/auto/, there is another way to control which image format is delivered to a client. In HTML 5, you can force the browser to automatically choose a WebP image version over others. This is done by using <picture>. Simply, wrap your <img> element with <picture> and add <source> having its type set to type="image/webp". Compatible browsers will then automatically load the WebP image version; others will take either JPEG or PNG.

  <source srcset="//" type="image/webp"/>
  <img src="//"/>



Sets the level of image quality that affects file sizes and hence loading speeds and volumes of generated traffic. quality works with JPEG and WebP images.

When your input and output are both JPEGs and no destructive operations are applied, your output image quality is limited to the initial input quality: when you upload a highly compressed image, you can use the normal setting or go even higher, but it will not affect neither your compression settings nor file size.

  • normal — the default setting, suits most cases.
  • better — can be used to render relatively small and detailed previews. ≈125% file size compared to normal.
  • best — useful for hi-res images, when you want to get perfect quality without paying much attention to file sizes. ≈170% file size.
  • lighter — useful when applied to relatively large images to save traffic without significant losses in quality. ≈80% file size.
  • lightest — useful for retina resolutions, when you don’t have to worry about the quality of each pixel. ≈50% file size.
  • smart — automatically adjusts image compression and format settings to preserve visual quality while minimizing the file size. The mode is content-aware. Image formats will not be adjusted if you define format explicitly.
Best quality, max file size
1x best 16Kb
Blurry on retina.
Smaller file size for all screens
1.5x lighter 16Kb
Fits all screens.
Even smaller file size, useful for retina
2x lightest 16Kb
Perfect for retina.
Smart compression, content aware, converts to WebP when possible
1x smart 14Kb

Progressive JPEG


Returns a progressive image. In progressive images, data are compressed in multiple passes of progressively higher detail. This is ideal for large images that will be displayed while downloading over a slow connection allowing a reasonable preview after receiving only a portion of the data. The operation does not affect non-JPEG images; does not force image formats to JPEG.

Baseline loading.

Progressive loading.

GIF to Video

Uploadcare Image Transformations features GIF to Video conversion that provides better loading times thus reducing your bounce rate. The feature is available on paid plans only.

GIF to Video workflow is the same as with other image transformations. The only difference is the gif2video URL directive should be included after the / separator, not /-/.


gif2video converts GIF files to video on the fly. Video files are much smaller than GIFs, without any quality loss. Their delivery to end users is much faster. In case your source file is not an animated GIF or the conversion feature is disabled for your project, you’ll get an HTTP 400 error.

Please note, even though you don’t use /-/ after :uuid with the gif2video directive, the separator is used with specific operations designed for the GIF to Video workflow: format and quality. We use such approach for our parser to tell the format and quality operations related to GIF to Video from their general versions.

Set Output Video Format, format


Converts an animated GIF to one of the following formats:

  • mp4 — H.264 video format. The format is supported by all major browsers. When no format is specified, mp4 is used by default.
  • webm — WebM video format. Supported in Google Chrome, Firefox, and Opera.

When embedding videos, the best practice is to specify both formats and let clients choose a more suitable one:

<video width="384" height="216" autoplay loop muted webkit-playsinline playsinline>
  <source src="" type="video/webm"/>
  <source src="" type="video/mp4"/>

Original GIF: 6.5MB, MP4: 251KB, WebM: 202KB

Set Output Video Quality, quality


Sets both quality and compression ratio for the output video. There are five :value levels: from better compression to better quality:
lightest, lighter, normal, better, best.

When quality is not explicitly specified, normal is used by default.