Transformations

There are two kinds of transformations: ones that actually modify the image (or video) and others that change the context of further transformations down the manipulation chain. You'll find both types listed here, in alphabetical order, each with a short description of its specific syntax and behavior.

background

Syntax: background=<color>

background specifies a color that will show through transparent and translucent parts of the image. This will have no effect on images with no transparency nor translucency.

If multiple background transformations are specified, they are applied in order. If a background uses an opaque color, any background coming after will be ignored.

contain

Syntax: contain=<size>

contain behaves like the CSS background size "contain". It will resize the image so that it completely fits inside the target area while conserving the original aspect ratio. The resulting image will be smaller than a target size which aspect ratio is not the same as the aspect ratio of the input.

For instance, applying contain=150x100 to our beloved face of a cat will result in the following 150x94 image:

Result

contain-max

Syntax: contain-max=<pixel size>

A conditional version of contain that will be applied only when one of the given lengths is smaller than the corresponding input image dimension.

contain-min

Syntax: contain-min=<pixel size>

A conditional version of contain that will be applied only when one of the given lengths is larger than the corresponding input image dimension.

cover

Syntax: cover=<size|ratio>

cover behaves like the CSS background size "cover". It will resize the image so that it completely fills the target area while conserving the original aspect ratio. If some parts of the image end up outside of the covered area, they are cropped.

So, a cover=100x100 of a 300x188 image would first scale the image down to a height of 100 pixels and then crop along the x-axis as demonstrated below:

Process	Result

cover will use the focus point as a guide and will crop the image so that the focus point is as central as possible in the resulting image. For instance, focus=85x85/cover=100x100 will behave as follows:

Process	Result

When a ratio is provided, cover will extract the biggest possible area that satisfies the ratio and is as centered on the focus point as possible. For instance, focus=85x85/cover=1:1 will behave as follows:

Process	Result

cover-max

Syntax: cover-max=<pixel size>

A conditional version of cover that will be applied only when one of the given lengths is smaller than the corresponding input image dimension.

cover-min

Syntax: cover-min=<pixel size>

A conditional version of cover that will be applied only when one of the given lengths is larger than the corresponding input image dimension.

crop

Syntax: crop=<crop size>[@<coordinates>]

crop will extract a zone from the image which size is the given crop size. If no coordinates are given, the focus point will be used as a guide to determine where to start the extraction. If coordinates are given, they will be used to determine the top-left pixel from which to start the extraction and the focus point will be reset to the center of the resulting image.

Here are two examples:

Manipulation	Process	Result
`crop=200x100`
`crop=200x100@20x50`

flip

Syntax: flip=<expression>

flip will invert the image horizontally, vertically or both depending on the expression provided.

Expression	Axis	Result
`both`	horizontal and vertical
`x`	horizontal
`y`	vertical

focus

Syntax: focus=<coordinates> or focus=auto

focus will set the focus point coordinates. It doesn't modify the output image in any way but will change the behavior of further transformations that take the focus point into account (namely cover, crop and resize).

If auto is used in place of actual coordinates, the focus point will be chosen automagically for you! Note that auto is not implemented for videos yet.

max

Syntax: max=<pixel size>

Alias of contain-max.

min

Syntax: min=<pixel size>

Alias of contain-min.

output

Syntax: output=<format>

Specifies the output format. It can be an image format, a video format or a preview format. Only the last output in the manipulation expression is taken into account. By default, TwicPics will "smart-guess" the best output format for the browser currently issueing the request but you can use output to override this behavior.

Available image formats are:

avif for AV1 Image File Format
heif for High Efficiency Image File Format
image (jpeg or webp depending on the browser, useful to extract the first frame of a video)
jpeg for Joint Photographic Experts Group
png for Portable Network Graphics
webp for WebP

Available video formats are:

h264 for an H.264 stream in an MPEG-4 Part 14 container
h265 for an H.265 stream in an MPEG-4 Part 14 container
vp9 for a VP9 stream in a WebM container

Available preview formats are:

blank: a blank, totally translucent version of the resulting image
maincolor: a solid color image containing the most represented color in the resulting image
meancolor: a solid color image containing the mean color of the resulting image
preview: a blurry preview of the resulting image

For videos, preview formats are based on the first frame of the resulting video.

Preview Format	Result
`output=blank`
`output=maincolor`
`output=meancolor`
`output=preview`

In addition, you can use output=auto to ensure TwicPics' "smart-guess" of the output image format is used even if an output format has already been specified by the default manipulation of your path.

quality

Syntax: quality=<number>

Specifies the output quality as a number between 1 and 100.

Note that quality will be ignored when:

output is png and truecolor is on
output is a preview format

quality-max

Syntax: quality-max=<number>

A conditional version of quality that will be applied only when given quality is below current quality.

Manipulation	Resulting quality
`quality=100/quality-max=50`	`50`
`quality=20/quality-max=50`	`20`
`quality-max=50/quality=100`	`100`

quality-min

Syntax: quality-min=<number>

A conditional version of quality that will be applied only when given quality is above current quality.

Manipulation	Resulting quality
`quality=100/quality-min=50`	`100`
`quality=20/quality-min=50`	`50`
`quality-min=50/quality=20`	`20`

resize

Syntax: resize=<size|ratio>

resize will resize the image to the specified size. If only one length is provided, the other dimension will be determined so as to respect the aspect ratio of the input image. If both lengths are provided, the aspect ratio may not be respected.

Here are three resize operations on the same source image:

Manipulation	Result
`resize=100`
`resize=-x100`
`resize=100x100`

If a ratio is provided, the image will be resized so that it stays as close as possible to its current surface (i.e number of pixels) while respecting the given aspect ratio as closely as possible.

For instance, focus=85x85/resize=4:3 will result in the following 274x206 image:

Result

The 300x188 image was resized to a 274x206 image (respecting the 4:3 ratio as best as possible). The initial surface was (300x188=) 56,400 pixels. The final surface is (274x206=) 56,444 pixels.

resize-max

Syntax: resize-max=<pixel size>

A conditional version of resize that will be applied only when one of the given lengths is smaller than the corresponding input image dimension.

resize-min

Syntax: resize-min=<pixel size>

A conditional version of resize that will be applied only when one of the given lengths is larger than the corresponding input image dimension.

truecolor

Syntax: truecolor=<boolean> or true-color=<boolean>

truecolor can be used to prevent color quantization. If no boolean is provided, true is assumed. By default, quantization is allowed (truecolor=false).

When may quantization occur? Whenever the output format is png. By default, TwicPics will quantize colors to reduce the size of the output image. It is possible to prevent this behaviour by setting truecolor to true.

Be aware that TwicPics will automatically output PNG images when:

no output format is specified,
the source image has an alpha channel,
and, target browser does not support WebP.

As such, use truecolor if you want to distribute substantially larger but more accurate images with translucency to users on browsers with no WebP support.

turn

Syntax: turn=<number> or turn=<expression>

turn will change the orientation of the image. It accepts an angle in degrees or an expression. Angles will be rounded to the closest multiple of 90°.