Image optimization
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Compression is essential for improving the performance of your website or application. Reducing image size without sacrificing quality and scaling operations are critical factors to consider.
Note: Keep in mind that when applying any image operation, a new file is created (cached on our CDN, and not counted towards your storage limits). This file is encoded with the default format and quality settings; however, you can adjust them to meet your requirements better.
We recommend setting your image quality on autopilot using the
-/quality/smart_retina/
operation. This will preserve visual quality while
minimizing the file size and choosing the most suitable output format.
Format
-/format/:format/
Converts 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 thesetfill
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
is 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.
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:
AVIF is activated for your project (contact sales);
output image resolution is under the threshold (currently 1 MPx);
image/avif
MIME type is supported by the client. - WebP is used when
image/webp
is 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.
Note: auto
works when you use primary Uploadcare storage (not S3
Bucket) and the default CDN domain ucarecdn.com
.
400x301 png 116KbTransparent | 400x301 jpeg 16KbOpaque | 400x301 webp 15KbTransparent, size is equal to the opaque one. |
HTML5 image auto format example
You can use <picture>
tag to render WebP image on client when possible. Place
<img>
within <picture>
and add <source>
with type="image/webp"
.
<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.
Quality
-/quality/:value/
Sets output JPEG and WebP quality. Since actual settings vary from codec to codec, and more importantly, from format to format, we provide five simple tiers and two automatic values which suits most cases of image distribution and are consistent.
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.
smart
— adjusts compression and format automatically to preserve visual quality while minimizing the file size. See the detailed explanation below.smart_retina
— similar tosmart
, yet optimized for double pixel density.normal
— the default behavior when noquality
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 tonormal
.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 compression
Smart quality modes analyze 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
define format
explicitly while using smart
and
smart_retina
. In this case, the image format won't be adjusted, but the
compression will. For example:
-/quality/smart/-/format/jpeg/
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, or we can
adjust quality more precisely for this case on the per-image basis with
smart_retina
preset.
1x best 16KbBlurry on retina. | 1.5x lighter 14Kb | 2x lightest 12KbPerfect for all screens. |
1x smart 9.6KbOptimized size for 1x. | 2x smart_retina 17KbOptimized size for retina displays. |
Progressive JPEG
-/progressive/yes/
-/progressive/no/
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. |
Meta information control
-/strip_meta/all/
-/strip_meta/none/
-/strip_meta/sensitive/
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 nostrip_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.
GIF 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 GIF to video operation.
Resize and crop
Rather than delivering large, full-sized images and relying on the browser to resize them, you can programmatically resize and crop them to reduce file weight further.