Manipulations

A manipulation is a list of transformations that are 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.

Transformations all have 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

Types of parameters

The TwicPics API strives to be as consistent as possible and, as such, transformations will use the same format for parameters that represent the same underlying concept.

boolean

A boolean represents... a boolean value (true or false).

The following literals are accepted:

• for true: true, on, yes
• for false: false, off, no

color

A color represents... a color! It can be specified as:

• a color name like red or green (see the comprehensive list further down this section)
• a three character hexadecimal value like 76E for RGB colors with no alpha,
• a four character hexadecimal value like 76E8 for RGB colors with alpha,
• a six character hexadecimal value like A68040 for RGB colors with no alpha,
• a eight character hexadecimal value like A6804080 for RGB colors with alpha,
• a CSS-like RGB expression: rgb(<red>,<green>,<blue>),
• a CSS-like RGBA expression: rgba(<red>,<green>,<blue>,<alpha>),
• a CSS-like HSL expression: hsl(<hue>,<saturation>,<lightness>),
• a CSS like HSLA expression: hsla(<hue>,<saturation>,<lightness>,<alpha>).

TwicPics also adds transparent so that you can easily create an invisible placeholder using placeholder:transparent.

Finally, you also have the possibility to add an alpha value to color names, three character hexadecimal colors, and six character hexadecimal color. Simply append the decimal part of the alpha component to the color expression.

Example	Result
violet.25
008.75
808080.3

Finally, here is the list of all supported color names:

Name	Preview
alice-blue
antique-white
aqua
aquamarine
azure
beige
bisque
black
blanched-almond
blue
blue-violet
brown
burlywood
cadet-blue
chartreuse
chocolate
coral
cornflower-blue
cornsilk
crimson
cyan
dark-blue
dark-cyan
dark-goldenrod
dark-gray
dark-green
dark-khaki
dark-magenta
dark-olive-green
dark-orange
dark-orchid
dark-red
dark-salmon
dark-sea-green
dark-slate-blue
dark-slate-gray
dark-turquoise
dark-violet
deep-pink
deep-sky-blue
dim-gray
dodger-blue
firebrick
floral-white
forest-green
fuchsia
gainsboro
ghost-white
gold
goldenrod
gray
green
green-yellow
honeydew
hot-pink
indian-red
indigo
ivory
khaki
lavender
lavender-blush
lawn-green
lemon-chiffon
light-blue
light-coral
light-cyan
light-goldenrod-yellow
light-gray
light-green
light-pink
light-salmon
light-sea-green
light-sky-blue
light-slate-gray
light-steel-blue
light-yellow
lime
lime-green
linen
magenta
maroon
medium-aquamarine
medium-blue
medium-orchid
medium-purple
medium-sea-green
medium-slate-blue
medium-spring-green
medium-turquoise
medium-violet-red
midnight-blue
mint-cream
misty-rose
moccasin
navajo-white
navy
old-lace
olive
olive-drab
orange
orange-red
orchid
pale-goldenrod
pale-green
pale-turquoise
pale-violet-red
papaya-whip
peach-puff
peru
pink
plum
powder-blue
purple
rebecca-purple
red
rosy-brown
royal-blue
saddle-brown
salmon
sandy-brown
sea-green
seashell
sienna
silver
sky-blue
slate-blue
slate-gray
snow
spring-green
steel-blue
tan
teal
thistle
tomato
turquoise
violet
wheat
white
white-smoke
yellow
yellow-green

coordinates

Coordinates represent a point in an image, specified as a couple of positive lengths separated by the character x:

• the first length is the coordinate along the x-axis (following the width of the image)
• the second length is the coordinate along the y-axis (following the height of the image)

TwicPics uses the same coordinate system as CSS: zero-based, left-to-right and top-to-bottom.

If we take the example of an image that is 640 pixel-wide and 480 pixel-high:

• 0x0 points to the top-left corner pixel
• 639x479 points to the bottom-right corner pixel.

crop size

A crop size is a size where omitted dimensions are assumed to be the same as the input image.

For instance:

• 320 and 320x- are equivalent to 320x1s
• -x240 is equivalent to 1sx240

length

TwicPics lengths are equivalent to CSS length values. They consist of a number eventually followed by a unit specifier:

• when no unit is specified, the length is in pixels, for instance 50 is a pixel length that can be read as "50 pixels"
• with the unit specifier "s", the length is a scale, for instance (1/3)s is a scale length that can be read as "one third"
• with the unit specifier "p", the length is a percentage, for instance 4.5p is a percentage length representing "4.5%"

number

TwicPics numbers can be JSON-encoded number literals or expressions that, when computed, result in an actual number. Expressions are embedded in parenthesis. Operators +, -, * and / are supported for additions, subtractions, multiplications and divisions respectively. Classic algebraic precedence is respected and parenthesis can be used to circumvent it.

For instance, 50, 7.2, (1/3), (5*(7+2)/3) are all valid numbers.

ratio

A ratio represents the proportional relationship between a width and a height. It is specified as a couple of strictly positive numbers separated by the character ::

• the first number is the number of length units contained in the width
• the second number is the number of length units contained in the height

For instance, the ratio 9:3 indicates that the width is 9-units long while the height is 3-units long. In terms of proportions, the width is (9/3=)3 times longer than the height.

size

A size represents a 2D area, specified as a couple of strictly positive lengths separated by the character x:

• the first length is the width of the area
• the second length is the height of the area

For instance 640x480 is 640 pixel-wide per 480 pixel-high.

It is possible to omit one of the dimensions using the character -. In that case, TwicPics will automatically compute the missing dimension so that the size respects the aspect ratio of the source image. For instance, if the source image is 640 pixel-wide per 480 pixel-high, then sizes 320x- and -x240 are both equivalent to 320x240.

As a shortcut, it is possible to omit the height by specifying just a width. For instance, the size 320 is equivalent to 320x-.

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.