Transformations

The complete reference of media transformations supported by the TwicPics API.

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.

Syntax

All transformations follow the same structure: <name>=<parameters>

where:

<name> is the name of the transformation
<parameters> is an expression specifying the parameters for the transformation

For instance:

resize=400 will resize the image to 400 pixels in width while conserving the source image aspect ratio
resize=640x480 will resize the image to exactly 640 pixels in width per 480 pixels in height, potentially altering its aspect ratio

Fundamentals

We refer to a list of one or several transformations as a manipulation .

Transformations can be chained together using the character /. There is no limit to the number of transformations you can chain, save for the limit in size of a URL as enforced by your browser. No matter how complex the manipulation, TwicPics will optimize it for speed and accuracy on the fly.

Focus point

Transformations behave differently depending on which point in the image is the main focus. TwicPics will do its best to keep this focus point as central as possible within the transformed image.

By default, the focus point is in the middle of the image but you can change its coordinates by using the focus transformation.

Chaining transformations

When adding a transformation to the chain, the parameters given are interpreted as if previous transformations had already been performed (ie. as if the source image was the result of the previous transformations).

For instance:

resize=340/resize=50p will result in an image that is 170 pixel-wide
resize=50p/focus=20x10 will put the focus point at coordinates 40x20 of the source image

Since TwicPics will optimize the manipulation, be aware that a transformation may shadow what came before it. For instance resize=50p/resize=340 will result in an image that is 340 pixel-wide: TwicPics will simply ignore the first resize.

List of transformations

achromatopsia

Syntax:

achromatopsia=<number>
achro=<number>
achromatopsia
achro

Corrects the colors of the image for color blind people suffering from achromatopsia.

The number provided must be between 0 and 1 and represents the degree of color blindness to correct for. If no number is provided then 1 (full color blindness) is assumed.

Manipulation	Result
none
`achromatopsia=0.5`
`achromatopsia`

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.

The background color will also fill the borders created by an inside transformation. This can be superceded by using the border transformation.

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

border

Syntax: border=<color>

border specifies a color to fill borders eventually created by an inside transformation. It supercedes background in that instance and it is notably possible to ensure both a solid background and translucent borders by using border=transparent. border will have no effect on images that have no inside applied to them.

If multiple border transformations are specified, they are applied in order. If a border uses an opaque color, any border thereafter 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`

deuteranopia

Syntax:

deuteranopia=<number>
deut=<number>
deuteranopia
deut

Corrects the colors of the image for color blind people suffering from deuteranopia.

The number provided must be between 0 and 1 and represents the degree of color blindness to correct for. If no number is provided then 1 (full color blindness) is assumed.

Manipulation	Result
none
`deuteranopia=0.5`
`deuteranopia`

flip

Syntax: flip=<axis>

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

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

focus

Syntax:

focus=<coordinates>
focus=<anchor>
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 zoom).

If an anchor is provided, then the focus point will be the corresponding corner or the middle point of the corresponding border.

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.

inside

Syntax: inside=<size|ratio>

inside behaves like the CSS background size "contain". It will resize the image so that it completely fits inside the target area. Contrary to the contain transformation, translucent borders will be added if the resulting aspect ratio is not the same as the aspect ratio of the input so that the resulting image has the exact, physical, size specified.

If the background transformation is used, then the background color will be used to fill the borders. If you wish to have a different color than the background color for the added borders, you can use the border transformation.

Expression	Result
`inside=150x150`
`background=black/inside=150x150`
`background=black/border=cyan/inside=150x150`

It is not possible to perform a crop after an inside.

max

Syntax: max=<pixel size>

Alias of contain-max.

min

Syntax: min=<pixel size>

Alias of contain-min.

output

Syntax:

output=<format>
output=<preview type>
output=auto

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 types are:

blank: a blank, totally translucent version of the resulting image
maincolor: a solid color image containing the most important 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, previews 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 format is used even if an output format has already been specified by the default manipulation of your path.

protanopia

Syntax:

protanopia=<number>
prot=<number>
protanopia
prot

Corrects the colors of the image for color blind people suffering from protanopia.

The number provided must be between 0 and 1 and represents the degree of color blindness to correct for. If no number is provided then 1 (full color blindness) is assumed.

Manipulation	Result
none
`protanopia=0.5`
`protanopia`

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.

tritanopia

Syntax:

tritanopia=<number>
trit=<number>
tritanopia
trit

Corrects the colors of the image for color blind people suffering from protanopia.

The number provided must be between 0 and 1 and represents the degree of color blindness to correct for. If no number is provided then 1 (full color blindness) is assumed.

Manipulation	Result
none
`tritanopia=0.5`
`tritanopia`

truecolor

Syntax:

truecolor=<boolean>
truecolor

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 that do not support WebP.