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The /image/resize Robot

We can resize, crop, and (auto-)rotate images, as well as watermark them.

The /image/resize Robot resizes, crops, changes colorization, rotation, and applies text and watermarks to images.

The /image/resize Robot resizes, crops, changes colorization, rotation, and applies text and watermarks to images.

Parameters

Name Type Default Description
use (required) String / Array of Strings / Object

General

Specifies which Step(s) to use as our input.

Special Step names

A special Step name is ":original", which provides user uploads handled by Transloadit. Outside of this restriction you can pick your own names.

Providing several Steps as input

You can add arrays to use several Steps: 
"use": [
  ":original",
  "encoded",
  "resized"
]
:bulb: That's likely all you need to know about use, but you can view advanced use cases:
› Advanced use cases

Step bundling

Some Robots can gather several Step results for a single invocation. For example, the /file/compress Robot would normally create one archive for each file passed to it. If you'd set bundle_steps to true, however, it will create one archive containing all the result files from all Steps you give it. To enable bundling, provide an object like the one below to the use parameter: 
"use": {
  "steps": [
    ":original",
    "encoded",
    "resized"
  ],
  "bundle_steps": true
}
This is also a crucial parameter for the /video/adaptive Robot, otherwise you'll generate 1 playlist for each viewing quality.
Keep in mind that all input Steps must be present in your Template. If one of them is missing (for instance it is rejected by a filter), no result is generated because the Robot waits indefinitely for all input Steps to be finished. Here's a demo that showcases Step bundling.

Group by original

Sticking with the /file/compress Robot example, you can set group_by_original to true, in order to create a separate archive for each of your uploaded or imported files, instead of creating one archive containing all originals (or one per resulting file). This is important for for the /media/playlist Robot where you'd typically set: 
"use": {
  "steps": [
    "segmented"
  ],
  "bundle_steps": true,
  "group_by_original": true
}

Fields

You can be more discriminatory by only using files that match a field name by setting the fields property. When this array is specified, the corresponding Step will only be executed for files submitted through one of the given field names, which correspond with the strings in the name attribute of the HTML file input field tag for instance. When using a back-end SDK, it corresponds with myFieldName1 in e.g.: $transloadit->addFile('myFieldName1', './chameleon.jpg'). This parameter is set to true by default, meaning all fields are accepted. Example: 
"use": {
  "steps": [ ":original" ],
  "fields": [ "myFieldName1" ]
}

Use As

Sometimes Robots take several inputs. For instance, the /video/merge Robot can create a slideshow from audio and images. You can map different Steps to the appropriate inputs. Example: 
"use": {
  "steps": [
    { "name": "audio_encoded", "as": "audio" },
    { "name": "images_resized", "as": "image" }
  ]
}
Sometimes the ordering is important, for instance, with our concat Robots. In these cases, you can add an index that starts at 1. You can also optionally filter by the multipart field name. Like in this example, where all files are coming from the same source (end-user uploads), but with different <input> names: Example: 
"use": {
  "steps": [
    { "name": ":original", "fields": "myFirstVideo", "as": "video_1" },
    { "name": ":original", "fields": "mySecondVideo", "as": "video_2" },
    { "name": ":original", "fields": "myThirdVideo", "as": "video_3" }
  ]
}
For times when it is not apparent where we should put the file, you can use Assembly Variables to be specific. For instance, you may want to pass a text file to the /image/resize Robot to burn the text in an image, but you are burning multiple texts, so where do we put the text file? We use specify it via ${use.text_1}, to indicate the first text file that was passed. Example: 
"watermarked": {
  "robot": "/image/resize",
  "use"  : {
    "steps": [
      { "name": "resized", as: "base" },
      { "name": "transcribed", as: "text" },
    ],
  },
  "text": [
    {
      "text"  : "Hi there",
      "valign": "top",
      "align" : "left",
    },
    {
      "text"    : "From the 'transcribed' Step: ${use.text_1}",
      "valign"  : "bottom",
      "align"   : "right",
      "x_offset": 16,
      "y_offset": -10,
    }
  ]
}
format String Auto The output format for the modified image. Some of the most important available formats are "jpg", "png", "gif", "tiff" and "pdf". For a complete lists of all formats that we can write to please check our supported image formats list. If this parameter is not specified it will default to the format of the input image.
width Integer(1-5000) Auto Width of the new image, in pixels. If not specified, will default to the width of the input image.
height Integer(1-5000) Auto Height of the new image, in pixels. If not specified, will default to the height of the input image.
resize_strategy String "fit" See the list of available resize strategies.
zoom Boolean true If this is set to false, smaller images will not be stretched to the desired width and height. For details about the impact of zooming for your preferred resize strategy, see the list of available resize strategies.
crop Object / JSON String null Specify an object containing coordinates for the top left and bottom right corners of the rectangle to be cropped from the original image(s). For example: 
{
  "x1": 80,
  "y1": 100,
  "x2": 160,
  "y2": 180
}
will crop the area from (80, 100) to (160, 180) which is a square whose width and height are 80px. If crop is set, the width and height parameters are ignored, and the resize_strategy is set to crop automatically. You can also use a JSON string of such an object with coordinates in similar fashion: "{ \"x1\": <Integer>, \"y1\": <Integer>, \"x2\": <Integer>, \"y2\": <Integer> }" To crop around human faces, see our /image/facedetect Robot.
gravity String center The direction from which the image is to be cropped, when "resize_strategy" is set to "crop", but no crop coordinates are defined. The available options are "center", "top", "bottom", "left", and "right". You can also combine options with a hyphen, such as "bottom-right".
strip Boolean false Strips all metadata from the image. This is useful to keep thumbnails as small as possible.
alpha String "" Gives control of the alpha/matte channel of an image. Valid options are "Activate", "Background", "Copy", "Deactivate", "Extract", "Off", "On", "Opaque", "Remove", "Set", "Shape", "Transparent"
preclip_alpha String "" Gives control of the alpha/matte channel of an image before applying the clipping path via clip: true. Valid options are "Activate", "Background", "Copy", "Deactivate", "Extract", "Off", "On", "Opaque", "Remove", "Set", "Shape", "Transparent"
flatten Boolean true Flattens all layers onto the specified background to achieve better results from transparent formats to non-transparent formats, as explained in the ImageMagick documentation. To preserve animations, GIF files are not flattened when this is set to true. To flatten GIF animations, use the frame parameter.
correct_gamma Boolean false Prevents gamma errors common in many image scaling algorithms.
quality Integer(1-100) Quality Controls the image compression for JPG and PNG images. Please also take a look at our /image/optimize Robot.
Before:


Quality 92 applied:


Quality 40 applied:


If this parameter is not specified it will default to the quality of the input image, or 92
background String "#FFFFFF" Either the hexadecimal code or name of the color used to fill the background (only used for the pad resize strategy). By default, the background of transparent images is changed to white. For details about how to preserve transparency across all image types, see this demo.
frame Integer / Null null Use this parameter when dealing with animated GIF files to specify which frame of the GIF is used for the operation. Specify 1 to use the first frame, 2 to use the second, and so on. null means all frames.
colorspace String "" Sets the image colorspace. For details about the available values, see the ImageMagick documentation. Please note that if you were using "RGB", we recommend using "sRGB" instead as of 2014-02-04. ImageMagick might try to find the most efficient colorspace based on the color of an image, and default to e.g. "Gray". To force colors, you might then have to use this parameter in combination with type "TrueColor"
type String "" Sets the image color type. For details about the available values, see the ImageMagick documentation. If you're using colorspace, ImageMagick might try to find the most efficient based on the color of an image, and default to e.g. "Gray". To force colors, you could e.g. set this parameter to "TrueColor"
sepia Integer(0-99) / Null null Sets the sepia tone in percent.
Before:


After setting sepia to 90:


After setting sepia to 40:


After setting sepia to 10:
rotation String / Boolean / Integer true Determines whether the image should be rotated. Set this to true to auto-rotate images that are rotated in a wrong way, or depend on EXIF rotation settings. You can also set this to an integer to specify the rotation in degrees. You can also specify "degrees" to rotate only when the image width exceeds the height (or "degrees" if the width must be less than the height). Specify false to disable auto-fixing of images that are rotated in a wrong way.
compress String / Null null Specifies pixel compression for when the image is written. Valid values are "None", "BZip", "Fax", "Group4", "JPEG", "JPEG2000", "Lossless", "LZW", "RLE", and "Zip". Compression is disabled by default. Please also take a look at our /image/optimize Robot.
blur String / Null null Specifies gaussian blur, using a value with the form {radius}x{sigma}. The radius value specifies the size of area the operator should look at when spreading pixels, and should typically be either "0" or at least two times the sigma value. The sigma value is an approximation of how many pixels the image is "spread"; think of it as the size of the brush used to blur the image. This number is a floating point value, enabling small values like "0.5" to be used.
progressive Boolean false Interlaces the image if set to true, which makes the image load progressively in browsers. Instead of rendering the image from top to bottom, the browser will first show a low-res blurry version of the images which is then quickly replaced with the actual image as the data arrives. This greatly increases the user experience, but comes at a cost of a file size increase by around 10%.
transparent String "" Make this color transparent within the image.
trim_whitespace Boolean false This determines if additional whitespace around the image should first be trimmed away. If you set this to true this parameter removes any edges that are exactly the same color as the corner pixels.
clip Boolean / String false Apply the clipping path to other operations in the resize job, if one is present. If set to true, it will automatically take the first clipping path. If set to a String it finds a clipping path by that name.
negate Boolean false Replace each pixel with its complementary color, effectively negating the image. Especially useful when testing clipping.
density String null While in-memory quality and file format depth specifies the color resolution, the density of an image is the spatial (space) resolution of the image. That is the density (in pixels per inch) of an image and defines how far apart (or how big) the individual pixels are. It defines the size of the image in real world terms when displayed on devices or printed. You can set this value to a specific width or in the format widthxheight. If your converted image has a low resolution, please try using the density parameter to resolve that.
output_meta Object {} Allows you to specify a set of metadata that is more expensive on cpu power to calculate, and thus is disabled by default to keep your Assemblies processing fast. You can add "has_transparency": true in this object to extract if the image contains transparent parts.
Text Overlay Parameters
Name Type Default Description
text Array of Objects [] An array of objects each containing text rules. The following text parameters are intended to be used as properties for your array of text overlays. Here is an example: 
"watermarked": {
  "use": "resized",
  "robot": "/image/resize",
  "imagemagick_stack": "v2.0.7",
  "text": [
    {
      "text": "© 2018 Transloadit.com",
      "size": 12,
      "font": "Ubuntu",
      "color": "#eeeeee",
      "valign": "bottom",
      "align": "right",
      "x_offset": 16,
      "y_offset": -10
    }
  ]
}

Before:


After:
text.*.font String "Arial" The font family to use. Also includes boldness and style of the font. Here is a list of all supported fonts.
text.*.size Integer 12 The text size in pixels.
text.*.rotate Integer 0 The rotation angle in degrees.
text.*.color String "#000000" The text color. All hex colors in the form "#xxxxxx" are supported, where each x can be 0-9 or a-f. "transparent" is also supported if you want a transparent text color. In that case use "stroke" instead, otherwise your text will not be visible.
text.*.background_color String "transparent" The text color. All hex colors in the form "#xxxxxx" are supported, where each x is can be 0-9 or a-f. "transparent" is also supported.
text.*.stroke_width Integer 0 The stroke's width in pixels.
text.*.stroke_color String "transparent" The stroke's color. All hex colors in the form "#xxxxxx" are supported, where each x is can be 0-9 or a-f. "transparent" is also supported.
text.*.align String "center" The horizontal text alignment. Can be "left", "center" and "right".
text.*.valign String "center" The vertical text alignment. Can be "top", "center" and "bottom".
text.*.x_offset Integer 0 The horizontal offset for the text in pixels that is added (positive integer) or removed (negative integer) from the horizontal alignment.
text.*.y_offset Integer 0 The vertical offset for the text in pixels that is added (positive integer) or removed (negative integer) from the vertical alignment.
Watermarking Parameters
Name Type Default Description
watermark_url String "" A URL indicating a PNG image to be overlaid above this image. Please note that you can also supply the watermark via another Assembly Step. With watermarking you can add an image onto another image. This is usually used for logos.

Before:


After:
watermark_position String / Array of Strings "center" The position at which the watermark is placed. The available options are "center", "top", "bottom", "left", and "right". You can also combine options, such as "bottom-right". An array of possible values can also be specified, in which case one value will be selected at random, such as [ "center", "left", "bottom-left", "bottom-right" ]. This setting puts the watermark in the specified corner. To use a specific pixel offset for the watermark, you will need to add the padding to the image itself.
watermark_x_offset Integer 0 The x-offset in number of pixels at which the watermark will be placed in relation to the position it has due to watermark_position. Values can be both positive and negative and yield different results depending on the watermark_position parameter. Positive values move the watermark closer to the image's center point, whereas negative values move the watermark further away from the image's center point.
watermark_y_offset Integer 0 The y-offset in number of pixels at which the watermark will be placed in relation to the position it has due to watermark_position. Values can be both positive and negative and yield different results depending on the watermark_position parameter. Positive values move the watermark closer to the image's center point, whereas negative values move the watermark further away from the image's center point.
watermark_size String "" The size of the watermark, as a percentage. For example, a value of "50%" means that size of the watermark will be 50% of the size of image on which it is placed. The exact sizing depends on watermark_resize_strategy, too.
watermark_resize_strategy String "fit" Available values are "fit", "stretch" and "area". To explain how the resize strategies work, let's assume our target image size is 800×800 pixels and our watermark image is 400×300 pixels. Let's also assume, the watermark_size parameter is set to "25%". For the "fit" resize strategy, the watermark is scaled so that the longer side of the watermark takes up 25% of the corresponding image side. And the other side is scaled according to the aspect ratio of the watermark image. So with our watermark, the width is the longer side, and 25% of the image size would be 200px. Hence, the watermark would be resized to 200×150 pixels. If the watermark_size was set to "50%"", it would be resized to 400×300 pixels (so just left at its original size). For the "stretch" resize strategy, the watermark is stretched (meaning, it is resized without keeping its aspect ratio in mind) so that both sides take up 25% of the corresponding image side. Since our image is 800×800 pixels, for a watermark size of 25% the watermark would be resized to 200×200 pixels. Its height would appear stretched, because keeping the aspect ratio in mind it would be resized to 200×150 pixels instead. For the "area" resize strategy, the watermark is resized (keeping its aspect ratio in check) so that it covers "xx%" of the video's surface area. The value from watermark_size is used for the percentage area size.
ImageMagick Parameters
Name Type Default Description
imagemagick_stack String "v1.0.0" Selects the ImageMagick stack version to use for encoding. These versions do not reflect any real ImageMagick versions, they reflect our own internal (non-semantic) versioning for our custom ImageMagick builds. The current recommendation is to use "v2.0.7" Other valid values can be found here.
See full docs

Demos

Our /image/resize Robot can be used in combination with other Robots, to create powerful workflows unique to your use case. Here are a few example scenarios that you can try live on our website:

Pricing

Transloadit is a SaaS with a subscription model.

Our /image/resize Robot counts towards your plan's data at a normal rate. It charges at minimum 0MB whenever it is used. Assuming the Startup Plan and an average image size of 0.8MB, you could convert 10240 images for $49/month.

Just like with your mobile plan, pricing goes down considerably when you commit to larger monthly volumes. You can adjust this every month. More info and available plans on our Pricing page.

Blog posts about the /image/resize Robot

We wrote the following posts about the /image/resize Robot on our blog: