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.
- Automating images with
-/format/auto/delivers the most efficient format that the client's browser supports.
- Further optimization of the image quality of the resulting image.
It's important to use all three types of operations to achieve the best
-/quality/smart/ operation that adjusts compression and
format automatically to preserve visual quality while minimizing the file size.
Check out our responsive images guide for more details.
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 original 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
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
Content-Disposition: attachment). Browsers may not show all image formats,
HEIC formats. If you need to display an image, add any image
-/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
- Animated images
Learn more about image processing limitations.
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:
Converts an image to one of the following formats:
jpegis a lossy image format (good compression for photos). JPEG doesn’t support an alpha channel; hence you can use the
setfilloperation that sets a background color. All browsers support JPEG.
pngis a lossless format (good compression only for graphics) with alpha channel support. All browsers support PNG.
webpis 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.
autois an automatic image format selection based on alpha channel presence and a client's device and browser.
Note: We partially support AVIF. See the next chapter for details.
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:
AVIF is activated for your project (contact our sales team);
output image resolution is under the threshold (currently 1 MPx);
image/avifMIME type is supported by the client.
- WebP is used when
image/webpis one of the supported MIME types.
- JPEG is used when the original image is fully opaque.
- PNG is used when the source image has an alpha channel with non-opaque pixels.
Transparent, size is equal
to the opaque one.
You can use
<picture> tag to render WebP image on client when possible. Place
<picture> and add
<picture> <source srcset="//ucarecdn.com/:uuid/:operations/-/format/webp/" type="image/webp"/> <img src="//ucarecdn.com/:uuid/:operations/-/format/jpeg/"/> </picture>html
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 and two automatic values 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
qualityoperation is applied. The reasonable quality for 1x pixel density.
smart— adjusts compression and format automatically to preserve visual quality while minimizing the file size. See the detailed explanation below.
smart_retina— similar to
smart, yet optimized for double pixel density.
better— can be used to render relatively small and detailed previews. ≈125% file size compared to
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.
Smart quality modes (
input images using content-aware algorithms to determine maximum compression
that won't cause noticeable visual artifacts.
Prior to compression, a smart mode selects an output image format. It can be PNG
for images with flat colors (like graphs, charts or web graphics). You can
format explicitly while using
smart_retina. In this case, the image format won't be adjusted, but the
compression will. For example:
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
lightest presets, or we can
adjust quality more precisely for this case on the per-image basis with
Blurry on retina.
Perfect for all screens.
Optimized size for 1x.
Optimized size for retina displays.
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
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_metaoperation 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.
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.