Image optimization

Image optimization is essential for improving the performance of your website or application. Resizing your images and compressing them without sacrificing quality are the critical factors to consider:

  • Scaling operations, such as various methods of resize and crop, have the biggest effect.
  • Delivering the most efficient format that the client's browser supports.
  • Further optimization of the image quality of the resulting image, especially for high pixel ratios.

It's important to use all three types of operations to achieve the best results.

Check out our responsive images guide for more details.

How it works

Every URL transformation generates a modified image version on the fly, while the original file stays intact. The transformed image version will be cached on CDN nodes to optimize delivery.

Also, you can fetch and deliver images to apply operations without explicitly uploading them:

When applying any image operation, a new file is created (cached on our CDN, and not counted towards your storage limits). If not set, this file is encoded with the default quality and format.

Image processing operation may be applied only to the appropriate file. On uploading, the file is analyzed by Uploadcare: file type, metadata, and so on; the file is assigned an attribute is_image. If this attribute is true, then an operation can be applied to the file. See the Limitations section.

Without any image processing operation in the URL, CDN instructs browsers to show images (Content-Disposition: inline) and download other file types (Content-Disposition: attachment). Browsers may not show all image formats, such as TIFF and HEIC. If you need to display an image, add any image processing operation, -/preview/ for instance.


Image processing operations have limits that you should consider:

  • Input image formats
  • Mandatory usage of core operations
  • File size
  • Output image dimensions
  • SVG files
  • Image resolution
  • Rotation
  • Animated images

Learn more about image processing limitations.

Scaling operations

Rather than delivering large, full-sized images and relying on the browser to resize them, you can do it programmatically:

The advanced scaling operations allows you to resize images more precisely:



If any other image processing operation is applied (such as scaling operations), the default format is auto (see how auto works).

Alternatively, you can use the -/format/ operation to convert an image to one of the following formats:

  • jpeg is a lossy image format (good compression 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 is a lossless format (good compression only for graphics) with alpha channel support. All browsers support PNG.
  • webp is a modern format with more efficient compression than JPEG and with alpha channel support. It works well for all images, yet not all browsers and OSs support it.
  • auto the default behavior; is an automatic image format selection based on alpha channel presenceand a client's device and browser.
  • preserve returns the image in the original format if it is PNG or JPEG, otherwise coerces to PNG or JPEG. This option is useful when you need to save the image, rather than display it to the end-user.

How auto works and prioritize image formats

First, the algorithm checks the Accept header with MIME types to figure out what image format a client browser supports.

  • AVIF is used as output when all the following conditions are met:
    • image/avif MIME type is supported by the client.
    • Output image resolution is under the threshold (currently 2 MPx).
  • WebP is used when image/webp MIME type is supported by the client.
  • PNG is used when the source image contains an alpha channel with non-opaque pixels or when the image has limited color diversity, resembling artwork.
  • JPEG is used otherwise.

You can disable the selection of modern formats, specifically AVIF and WebP, for your project in the Dashboard. Alternatively, you may consider adding the -/format/preserve/ operation to a specific URL.

Note: auto works when you use primary Uploadcare storage (not S3 Bucket) and the default Uploadcare 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 PNG

400x301 webp 15Kb
Transparent, size is equal
to the opaque one.

Browsers that support WebP will load this image version, while others will display JPEG or PNG instead.



Sets output quality for lossy formats (JPEG, WebP, and AVIF). Since actual settings vary from codec to codec and, more importantly, from format to format, we provide five simple tiers that are consistent across different formats and other settings and suit most cases of image distribution.

A higher quality level will typically result in a larger output file. However, setting the quality level higher than the original level of the uploaded image won’t increase your file size.

  • normal — the default behavior when no quality operation is applied. The reasonable quality for 1x pixel density.
  • better — can be used to render relatively small and detailed previews. ≈125% file size compared to normal.
  • best — can be used to deliver images close to their pristine quality (e.g., for artwork). ≈170% file size.
  • lighter — useful when applied to relatively large images to save traffic without significant quality loss. ≈80% file size.
  • lightest — highest compression ratio for high pixel ratio. ≈50% file size.

Adaptive quality

Adaptive quality could be enabled per project in the Dashboard. In this case, we analyze the output image using content-aware algorithms to determine maximum compression that won't cause noticeable visual artefacts and adjust the compression level accordingly.

Optimizing for high pixel ratios

A great approach for high pixel densities is to increase images resolution and reduce quality at the same time. Compared to just increasing quality, images will look clearer on all screens with nearly the same file size. To adjust quality, you can use lighter and lightest presets.

Best quality, max file size

1x best 16Kb
Blurry on retina.

Smaller file size for all screens

1.5x lighter 14Kb

Even smaller file size, useful for retina

2x lightest 12Kb
Perfect for all screens.

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.

Strip meta information


The original image often comes with additional information built into the image file. In most cases, this information doesn't affect image rendering and thus can be safely stripped from the processed images to reduce image weight. Currently, you can only keep EXIF meta information. Other storage, such as XMP or IPTC, will always be stripped when creating a new processed image version.

  • all — the default behavior when no strip_meta operation is applied. No meta information will be added to the processed file.
  • none — uses the EXIF from the original file. The orientation tag will be set to 1 (normal orientation).
  • sensitive — uses the EXIF from the original file but skips geolocation. The orientation tag will be set to 1 (normal orientation).

If you need to restrict user access to EXIF information, please protect your images from editing.

Animated images optimization

Video files are much smaller than GIFs, without noticeable quality loss. Their delivery to end users is much faster. Gif to video operation converts animated image files, such as GIF, WebP, and HEIC, to video and transforms them on the fly. Learn more about animated images optimization.