Imagor

Imagor is a fast, Docker-ready image processing server written in Go.

Imagor uses one of the most efficient image processing library libvips (with govips). It is typically 4-8x faster than using the quickest ImageMagick and GraphicsMagick settings.

Imagor is a Go library that is easily extensible, ready to be installed and used in any Unix environment, and ready to be containerized using Docker.

Imagor adopts the Thumbor URL syntax and covers most of the web image processing use cases. If these fit your requirements, Imagor would be a lightweight, high performance drop-in replacement.

Quick Start

docker run -p 8000:8000 shumc/imagor -imagor-unsafe

Try out the following image URLs:

# original images
https://raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png
https://raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher-front.png

http://localhost:8000/unsafe/500x500/top/https://raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png
http://localhost:8000/unsafe/fit-in/500x500/filters:fill(white):format(jpeg)/raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png
http://localhost:8000/unsafe/fit-in/-500x500/10x10/filters:hue(290):saturation(100):fill(yellow):format(jpeg):quality(80)/raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png
http://localhost:8000/unsafe/fit-in/800x800/filters:fill(white):watermark(raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher-front.png,repeat,bottom,10):format(jpeg)/raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png

Docker Compose Example

Imagor with File Loader and Storage using mounted volume:

version: "3"
services:
  imagor:
    image: shumc/imagor:latest
    volumes:
      - ./:/mnt/data
    environment:
      PORT: 8000
      IMAGOR_UNSAFE: 1 # unsafe URL for testing
      FILE_LOADER_BASE_DIR: /mnt/data # enable file loader by specifying base dir
      FILE_STORAGE_BASE_DIR: /mnt/data # enable file storage by specifying base dir
    ports:
      - "8000:8000"

Imagor with AWS S3 Loader and Storage:

version: "3"
services:
  imagor:
    image: shumc/imagor:latest
    environment:
      PORT: 8000
      IMAGOR_SECRET: mysecret # secret key for URL signature
      AWS_ACCESS_KEY_ID: ...
      AWS_SECRET_ACCESS_KEY: ...
      AWS_REGION: ...
      S3_LOADER_BUCKET: mybucket # enable S3 loader by specifying loader bucket
      S3_LOADER_BASE_DIR: images # optional
      S3_STORAGE_BUCKET: mybucket # enable S3 storage by specifying storage bucket
      S3_STORAGE_BASE_DIR: images # optional
    ports:
      - "8000:8000"

Imagor Endpoint

Imagor endpoint is a series of URL parts which defines the image operations, followed by the image URI:

/HASH|unsafe/trim/AxB:CxD/fit-in/stretch/-Ex-F/GxH/HALIGN/VALIGN/smart/filters:NAME(ARGS):NAME(ARGS):.../IMAGE

• HASH is the URL Signature hash, or unsafe if unsafe mode is used
• trim removes surrounding space in images using top-left pixel color
• AxB:CxD means manually crop the image at left-top point AxB and right-bottom point CxD
• fit-in means that the generated image should not be auto-cropped and otherwise just fit in an imaginary box specified by ExF
• stretch means resize the image to ExF without keeping its aspect ratios
• -Ex-F means resize the image to be ExF of width per height size. The minus signs mean flip horizontally and vertically
• GxH add horizontal padding G and vertical padding H under fit-in
• HALIGN is horizontal alignment of crop. Accepts left, right or center, defaults to center
• VALIGN is vertical alignment of crop. Accepts top, bottom or middle, defaults to middle
• smart means using smart detection of focal points
• filters a pipeline of image filter operations to be applied, see filters section
• IMAGE is the image URI

Imagor provides utilities for previewing and generating Imagor endpoint URI:

GET /params

Prepending /params to the existing endpoint returns the endpoint attributes in JSON form, useful for preview:

curl http://localhost:8000/params/g5bMqZvxaQK65qFPaP1qlJOTuLM=/fit-in/500x400/0x20/filters:fill(white)/raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png

{
  "path": "fit-in/500x400/0x20/filters:fill(white)/raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png",
  "image": "raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png",
  "hash": "g5bMqZvxaQK65qFPaP1qlJOTuLM=",
  "fit_in": true,
  "width": 500,
  "height": 400,
  "v_padding": 20,
  "filters": [
    {
      "name": "fill",
      "args": "white"
    }
  ]
}

imagorpath package

Imagor Go library provides a imagorpath package which allows you to parse and generate Imagor endpoint using the Params struct:

import "github.com/cshum/imagor/imagorpath"

...

func Test(t *testing.T) {
	params := imagorpath.Params{
		Image:    "raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png",
		FitIn:    true,
		Width:    500,
		Height:   400,
		VPadding: 20,
		Filters: imagorpath.Filters{
			{
				Name: "fill",
				Args: "white",
			},
		},
	}

	// generate signed Imagor endpoint from Params struct with secret
	path := imagorpath.Generate(params, "mysecret")

	assert.Equal(t, path, "g5bMqZvxaQK65qFPaP1qlJOTuLM=/fit-in/500x400/0x20/filters:fill(white)/raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png")
}

URL Signature

In production environment, it is highly recommended turning off IMAGOR_UNSAFE and setup IMAGOR_SECRET to avoid DDoS attacks that abuse multiple image operations.

The hash is based on HMAC digest, created by taking the URL path (excluding /unsafe/) with secret. The hash is then base64url-encoded. An example in Go:

func SignPath(path, secret string) string {
	h := hmac.New(sha1.New, []byte(secret))
	h.Write([]byte(strings.TrimPrefix(path, "/")))
	hash := base64.URLEncoding.EncodeToString(h.Sum(nil))
	return hash + "/" + path
}

func main() {
	fmt.Println(SignPath("500x500/top/raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png", "mysecret"))
	// RArq3FZw_bqxLcpKo1WI0aX_q7s=/fit-in/500x500/filters:fill(white):format(jpeg)/raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher.png
}

Filters

Filters /filters:NAME(ARGS):NAME(ARGS):.../ is a pipeline of image operations that will be sequentially applied to the image. Examples:

/filters:fill(white):format(jpeg)/
/filters:hue(290):saturation(100):fill(yellow):format(jpeg):quality(80)/
/filters:fill(white):watermark(raw.githubusercontent.com/golang-samples/gopher-vector/master/gopher-front.png,repeat,bottom,10):format(jpeg)/

Imagor supports the following filters:

• background_color(color) sets the background color of a transparent image
  • color the color name or hexadecimal rgb expression without the “#” character
• blur(sigma) applies gaussian blur to the image
• brightness(amount) increases or decreases the image brightness
  • amount -100 to 100, the amount in % to increase or decrease the image brightness
• contrast(amount) increases or decreases the image contrast
  • amount -100 to 100, the amount in % to increase or decrease the image contrast
• fill(color) fill the missing area or transparent image with the specified color:
  • color - color name or hexadecimal rgb expression without the “#” character
    • If color is "blur" - missing parts are filled with blurred original image.
    • If color is "auto" - the top left image pixel will be chosen as the filling color
• format(format) specifies the output format of the image
  • format accepts jpeg, png, webp, gif, jp2, tiff
• grayscale() changes the image to grayscale
• hue(angle) increases or decreases the image hue
  • angle the angle in degree to increase or decrease the hue rotation
• quality(amount) changes the overall quality of the image, does nothing for png
  • amount 0 to 100, the quality level in %
• rgb(r,g,b) amount of color in each of the rgb channels in %. Can range from -100 to 100
• rotate(angle) rotates the given image according to the angle value passed
  • angle accepts 0, 90, 180, 270
• round_corner(rx [, ry [, color]]) adds rounded corners to the image with the specified color as background
  • rx, ry amount of pixel to use as radius. ry = rx if ry is not provided
  • color the color name or hexadecimal rgb expression without the “#” character
• saturation(amount) increases or decreases the image saturation
  • amount -100 to 100, the amount in % to increase or decrease the image saturation
• sharpen(sigma) sharpens the image
• trim([tolerance [, position]]) apply trim operation as part of the filter pipeline
  • tolerance the euclidean distance between the colors to get trimmed within the tolerance, default 1
  • position default using top-left pixel color unless specified bottom-right
• upscale() upscale the image if fit-in is used
• watermark(image, x, y, alpha [, w_ratio [, h_ratio]]) adds a watermark to the image. It can be positioned inside the image with the alpha channel specified and optionally resized based on the image size by specifying the ratio
  • image watermark image URI, using the same image loader configured for Imagor
  • x horizontal position that the watermark will be in:
    • Positive numbers indicate position from the left and negative numbers indicate position from the right.
    • Number followed by a p e.g. 20p means calculating the value from the image width as percentage
    • left,right,center positioned left, right or centered respectively
    • repeat the watermark will be repeated horizontally
  • y vertical position that the watermark will be in:
    • Positive numbers indicate position from the top and negative numbers indicate position from the bottom.
    • Number followed by a p e.g. 20p means calculating the value from the image height as percentage
    • top,bottom,center positioned top, bottom or centered respectively
    • repeat the watermark will be repeated vertically
  • alpha watermark image transparency, a number between 0 (fully opaque) and 100 (fully transparent).
  • w_ratio percentage of the width of the image the watermark should fit-in
  • h_ratio percentage of the height of the image the watermark should fit-in

Configurations

Imagor supports command-line arguments, see available options imagor -h. You may check main.go for better understanding the initialization sequences.

Imagor also supports environment variables or .env file for the arguments equivalent in capitalized snake case. For instances -imagor-secret would become IMAGOR_SECRET:

# both are equivalent

imagor -debug -imagor-secret=1234

DEBUG=1 IMAGOR_SECRET=1234 imagor

Available options:

imagor -h
Usage of imagor:
  -debug
        Debug mode
  -port int
        Sever port (default 8000)

  -imagor-secret string
        Secret key for signing Imagor URL
  -imagor-unsafe
        Unsafe Imagor that does not require URL signature. Prone to URL tampering
  -imagor-version
        Imagor version
  -imagor-cache-header-ttl duration
        Imagor HTTP cache header ttl for successful image response (default 24h0m0s)
  -imagor-request-timeout duration
        Timeout for performing imagor request (default 30s)
  -imagor-load-timeout duration
        Timeout for Imagor Loader request, should be smaller than imagor-request-timeout (default 20s)
  -imagor-save-timeout duration
        Timeout for saving image for storage (default 1m0s)

  -server-address string
        Server address
  -server-cors
        Enable CORS
  -server-strip-query-string
        Enable strip query string redirection
  -server-path-prefix string
        Server path prefix

  -vips-concurrency-level int
        VIPS concurrency level. Default to the number of CPU cores.
  -vips-disable-blur
        VIPS disable blur operations for vips processor
  -vips-disable-filters string
        VIPS disable filters by csv e.g. blur,watermark,rgb
  -vips-max-filter-ops int
        VIPS maximum number of filter operations allowed (default 10)

  -http-loader-allowed-sources string
        HTTP Loader allowed hosts whitelist to load images from if set. Accept csv wth glob pattern e.g. *.google.com,*.github.com.
  -http-loader-default-scheme string
        HTTP Loader default scheme if not specified by image path. Set "nil" to disable default scheme. (default "https")
  -http-loader-forward-headers string
        Forward request header to HTTP Loader request by csv e.g. User-Agent,Accept
  -http-loader-forward-all-headers
        Forward all request headers to HTTP Loader request
  -http-loader-insecure-skip-verify-transport
        HTTP Loader to use HTTP transport with InsecureSkipVerify true
  -http-loader-max-allowed-size int
        HTTP Loader maximum allowed size in bytes for loading images if set
  -http-loader-disable
        Disable HTTP Loader

  -file-loader-base-dir string
        Base directory for File Loader. Will activate File Loader only if this value present
  -file-loader-path-prefix string
        Base path prefix for File Loader

  -file-storage-base-dir string
        Base directory for File Storage. Will activate File Storage only if this value present
  -file-storage-path-prefix string
        Base path prefix for File Storage
  -file-storage-mkdir-permission string
        File Storage mkdir permission (default "0755")
  -file-storage-write-permission string
        File Storage write permission (default "0666")

  -aws-access-key-id string
        AWS Access Key ID. Required if using S3 Loader or S3 Storage
  -aws-region string
        AWS Region. Required if using S3 Loader or S3 Storage
  -aws-secret-access-key string
        AWS Secret Access Key. Required if using S3 Loader or S3 Storage

  -s3-loader-base-dir string
        Base directory for S3 Loader
  -s3-loader-bucket string
        S3 Bucket for S3 Loader. Will activate S3 Loader only if this value present
  -s3-loader-path-prefix string
        Base path prefix for S3 Loader

  -s3-storage-base-dir string
        Base directory for S3 Storage
  -s3-storage-bucket string
        S3 Bucket for S3 Storage. Will activate S3 Storage only if this value present
  -s3-storage-path-prefix string
        Base path prefix for S3 Storage
  -s3-storage-acl string
        Upload ACL for S3 Storage (default "public-read")