Imagor

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

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

Imagor is a Go application that is highly optimized for concurrent requests. It is ready to be installed and used in any Unix environment, and ready to be containerized using Docker.

Imagor adopts the Thumbor URL syntax and supports tons of image processing use cases representing a lightweight, high-performance drop-in replacement.

Quick Start

docker run -p 8000:8000 ghcr.io/cshum/imagor -imagor-unsafe -imagor-auto-webp

Original images:

https://raw.githubusercontent.com/cshum/imagor/master/testdata/gopher.png
https://raw.githubusercontent.com/cshum/imagor/master/testdata/dancing-banana.gif
https://raw.githubusercontent.com/cshum/imagor/master/testdata/gopher-front.png

Try out the following image URLs:

http://localhost:8000/unsafe/fit-in/200x200/filters:fill(white)/https://raw.githubusercontent.com/cshum/imagor/master/testdata/gopher.png
http://localhost:8000/unsafe/200x200/smart/filters:fill(white):format(jpeg):quality(80)/https://raw.githubusercontent.com/cshum/imagor/master/testdata/gopher.png
http://localhost:8000/unsafe/fit-in/-180x180/10x10/filters:hue(290):saturation(100):fill(yellow)/raw.githubusercontent.com/cshum/imagor/master/testdata/gopher.png
http://localhost:8000/unsafe/30x40:100x150/filters:fill(cyan)/raw.githubusercontent.com/cshum/imagor/master/testdata/dancing-banana.gif
http://localhost:8000/unsafe/fit-in/200x150/filters:fill(yellow):watermark(raw.githubusercontent.com/cshum/imagor/master/testdata/gopher-front.png,repeat,bottom,0,40,40)/raw.githubusercontent.com/cshum/imagor/master/testdata/dancing-banana.gif

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:IxJ/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. Coordinates can also be provided as float values between 0 and 1 (percentage of image dimensions)
• 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:IxJ add left-top padding GxH and right-bottom padding IxJ
• 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, including the imagorpath Go package and the /params endpoint:

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/cshum/imagor/master/testdata/gopher.png

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

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/cshum/imagor/master/testdata/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
• focal(AxB:CxD) adds a focal region for custom transformations, coordinated by left-top point AxB and right-bottom point CxD. Also accepts float values between 0 and 1 that represents percentage of image dimensions.
• format(format) specifies the output format of the image
  • format accepts jpeg, png, gif, webp, tiff, avif
• 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
• max_bytes(amount) automatically degrades the quality of the image until the image is under the specified amount of bytes
• proportion(percentage) scales image to the proportion percentage of the image dimension
• 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
• 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

Loader, Storage and Result Storage

Imagor Loader, Storage and Result Storage are the building blocks for loading and saving images from various sources:

• Loader loads image. Enable Loader where you wish to load images from, but without modifying it e.g. static directory.
• Storage loads and saves image. This allows subsequent requests for the same image loads directly from the storage, instead of HTTP source.
• Result Storage loads and saves the processed image. This allows subsequent request of the same parameters loads from the result storage, saving processing resources.

Imagor provides built-in adaptors that support HTTP(s), Proxy, File System, AWS S3 and Google Cloud Storage. By default, HTTP Loader is used as fallback. You can choose to enable additional adaptors that fit your use cases.

File System

Docker Compose example with file system, using mounted volume:

version: "3"
services:
  imagor:
    image: ghcr.io/cshum/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
      FILE_STORAGE_MKDIR_PERMISSION: 0755 # optional
      FILE_STORAGE_WRITE_PERMISSION: 0666 # optional

      FILE_RESULT_STORAGE_BASE_DIR: /mnt/data/result # enable file result storage by specifying base dir
      FILE_RESULT_STORAGE_MKDIR_PERMISSION: 0755 # optional
      FILE_RESULT_STORAGE_WRITE_PERMISSION: 0666 # optional
      
    ports:
      - "8000:8000"

AWS S3

Docker Compose example with AWS S3. Also works with S3 compatible such as MinIO, DigitalOcean Space.

version: "3"
services:
  imagor:
    image: ghcr.io/cshum/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 bucket
      S3_LOADER_BASE_DIR: images # optional

      S3_STORAGE_BUCKET: mybucket # enable S3 storage by specifying bucket
      S3_STORAGE_BASE_DIR: images # optional
      S3_STORAGE_ACL: public-read # optional - see https://docs.aws.amazon.com/AmazonS3/latest/userguide/acl-overview.html#canned-acl

      S3_RESULT_STORAGE_BUCKET: mybucket # enable S3 result storage by specifying bucket
      S3_RESULT_STORAGE_BASE_DIR: images/result # optional
      S3_RESULT_STORAGE_ACL: public-read # optional
    ports:
      - "8000:8000"

Custom S3 Endpoint

Configure custom S3 endpoint for S3 compatible such as MinIO, DigitalOcean Space:

      S3_ENDPOINT: http://minio:9000
      S3_FORCE_PATH_STYLE: 1

By default, S3 prepends bucket name as subdomain to the request URL:

http://mybucket.minio:9000/image.jpg

this may not be desirable for a self-hosted endpoint. You can also switch to path-style requests using S3_FORCE_PATH_STYLE=1 such that the host remains unchanged:

http://minio:9000/mybucket/image.jpg

Google Cloud Storage

Docker Compose example with Google Cloud Storage:

version: "3"
services:
  imagor:
    image: ghcr.io/cshum/imagor:latest
    volumes:
      - ./googlesecret:/etc/secrets/google
    environment:
      PORT: 8000
      IMAGOR_SECRET: mysecret # secret key for URL signature
      GOOGLE_APPLICATION_CREDENTIALS: /etc/secrets/google/appcredentials.json # google cloud secrets file

      GCLOUD_LOADER_BUCKET: mybucket # enable loader by specifying bucket
      GCLOUD_LOADER_BASE_DIR: images # optional

      GCLOUD_STORAGE_BUCKET: mybucket # enable storage by specifying bucket
      GCLOUD_STORAGE_BASE_DIR: images # optional
      GCLOUD_STORAGE_ACL: publicRead # optional - see https://cloud.google.com/storage/docs/json_api/v1/objects/insert

      GCLOUD_RESULT_STORAGE_BUCKET: mybucket # enable result storage by specifying bucket
      GCLOUD_RESULT_STORAGE_BASE_DIR: images/result # optional
      GCLOUD_RESULT_STORAGE_ACL: publicRead # optional
    ports:
      - "8000:8000"

Security

URL Signature

In production environment, it is highly recommended turning off IMAGOR_UNSAFE and setting up URL signature using IMAGOR_SECRET, to prevent DDoS attacks that abuse multiple image operations.

The URL signature hash is based on SHA digest, created by taking the URL path (excluding /unsafe/) with secret. The hash is then Base64 URL encoded. An example in Node.js:

var hmacSHA1 = require("crypto-js/hmac-sha1")
var Base64 = require("crypto-js/enc-base64")

function sign(path, secret) {
  var hash = hmacSHA1(path, secret)
  hash = Base64.stringify(hash).replace(/\+/g, '-').replace(/\//g, '_')
  return hash + '/' + path
}

console.log(sign('500x500/top/raw.githubusercontent.com/cshum/imagor/master/testdata/gopher.png', 'mysecret'))
// cST4Ko5_FqwT3BDn-Wf4gO3RFSk=/500x500/top/raw.githubusercontent.com/cshum/imagor/master/testdata/gopher.png

Custom HMAC Signer

Imagor uses SHA1 HMAC signer by default, the same one used by Thumbor. However, SHA1 is not considered cryptographically secure. If that is a concern it is possible to configure different signing method and truncate length. Imagor supports sha1, sha256, sha512 signer type:

IMAGOR_SIGNER_TYPE=sha256
IMAGOR_SIGNER_TRUNCATE=32

The URL signature generator then becomes:

var hmacSHA256 = require("crypto-js/hmac-sha256")
var Base64 = require("crypto-js/enc-base64")

function sign(path, secret) {
  var hash = hmacSHA256(path, secret)
  hash = Base64.stringify(hash).slice(0, 32).replace(/\+/g, '-').replace(/\//g, '_')
  return hash + '/' + path
}

Allowed Sources

Whitelist specific hosts to restrict loading images only from the allowed sources using HTTP_LOADER_ALLOWED_SOURCES. Accept csv wth glob pattern e.g.:

HTTP_LOADER_ALLOWED_SOURCES=*.foobar.com,my.foobar.com,mybucket.s3.amazonaws.com

Configuration

Imagor supports command-line arguments and environment variables for the arguments equivalent in capitalized snake case, see available options imagor -h. For instances -imagor-secret would become IMAGOR_SECRET:

# both are equivalent

imagor -debug -imagor-secret 1234

DEBUG=1 IMAGOR_SECRET=1234 imagor

Configuration can also be specified in a .env environment variable file and referenced with the -config flag:

imagor -config path/to/config.env

config.env:

PORT=8000
IMAGOR_SECRET=mysecret
DEBUG=1

Available options

imagor -h
Usage of imagor:
  -debug
        Debug mode
  -port int
        Sever port (default 8000)
  -version
        Imagor version
  -config string
        Retrieve configuration from the given file (default ".env")

  -imagor-secret string
        Secret key for signing Imagor URL
  -imagor-unsafe
        Unsafe Imagor that does not require URL signature. Prone to URL tampering
  -imagor-auto-webp
        Output WebP format automatically if browser supports
  -imagor-auto-avif
        Output AVIF format automatically if browser supports (experimental)
  -imagor-base-params string
        Imagor endpoint base params that applies to all resulting images e.g. fitlers:watermark(example.jpg)
  -imagor-signer-type string
        Imagor URL signature hasher type sha1, sha256, sha512 (default "sha1")
  -imagor-signer-truncate int
        Imagor URL signature truncate at length
  -imagor-cache-header-ttl duration
        Imagor HTTP cache header ttl for successful image response (default 168h0m0s)
  -imagor-cache-header-swr duration
        Imagor HTTP Cache-Control header stale-while-revalidate for successful image response (default 24h0m0s)
  -imagor-cache-header-no-cache
        Imagor HTTP Cache-Control header no-cache for successful image response
  -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 to Imagor Storage (default 20s)
  -imagor-process-timeout duration
        Timeout for image processing (default 20s)
  -imagor-process-concurrency int
        Imagor semaphore size for process concurrency control. Set -1 for no limit (default -1)
  -imagor-base-path-redirect string
        URL to redirect for Imagor / base path e.g. https://www.google.com
  -imagor-modified-time-check
        Check modified time of result image against the source image. This eliminates stale result but require more lookups
  -imagor-disable-params-endpoint
        Imagor disable /params endpoint
  -imagor-disable-error-body
        Imagor disable response body on error

  -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
  -server-access-log
        Enable server access log

  -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-forward-headers string
        Forward request header to HTTP Loader request by csv e.g. User-Agent,Accept
  -http-loader-forward-client-headers
        Forward browser client 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-proxy-urls string
        HTTP Loader Proxy URLs. Enable HTTP Loader proxy only if this value present. Accept csv of proxy urls e.g. http://user:pass@host:port,http://user:pass@host:port
  -http-loader-proxy-allowed-sources string
        HTTP Loader Proxy allowed hosts that enable proxy transport, if proxy URLs are 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-accept string
        HTTP Loader set request Accept header and validate response Content-Type header (default "*/*") 
  -http-loader-disable
        Disable HTTP Loader

  -file-safe-chars string
        File safe characters to be excluded from image key escape
  -file-loader-base-dir string
        Base directory for File Loader. Enable File Loader only if this value present
  -file-loader-path-prefix string
        Base path prefix for File Loader
  -file-result-storage-base-dir string
        Base directory for File Result Storage. Enable File Result Storage only if this value present
  -file-result-storage-mkdir-permission string
        File Result Storage mkdir permission (default "0755")
  -file-result-storage-path-prefix string
        Base path prefix for File Result Storage
  -file-result-storage-write-permission string
        File Storage write permission (default "0666")
  -file-result-storage-expiration duration
        File Result Storage expiration duration e.g. 24h. Default no expiration
  -file-storage-base-dir string
        Base directory for File Storage. Enable 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")
  -file-storage-expiration duration
        File Storage expiration duration e.g. 24h. Default no expiration

  -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-endpoint string
        Optional S3 Endpoint to override default
  -s3-safe-chars string
        S3 safe characters to be excluded from image key escape
  -s3-force-path-style
        S3 force the request to use path-style addressing s3.amazonaws.com/bucket/key, instead of bucket.s3.amazonaws.com/key
  -s3-loader-bucket string
        S3 Bucket for S3 Loader. Enable S3 Loader only if this value present
  -s3-loader-base-dir string
        Base directory for S3 Loader
  -s3-loader-path-prefix string
        Base path prefix for S3 Loader
  -s3-result-storage-bucket string
        S3 Bucket for S3 Result Storage. Enable S3 Result Storage only if this value present
  -s3-result-storage-base-dir string
        Base directory for S3 Result Storage
  -s3-result-storage-path-prefix string
        Base path prefix for S3 Result Storage
  -s3-result-storage-acl string
        Upload ACL for S3 Result Storage (default "public-read")
  -s3-result-storage-expiration duration
        S3 Result Storage expiration duration e.g. 24h. Default no expiration
  -s3-storage-bucket string
        S3 Bucket for S3 Storage. Enable S3 Storage only if this value present
  -s3-storage-base-dir string
        Base directory for S3 Storage
  -s3-storage-path-prefix string
        Base path prefix for S3 Storage
  -s3-storage-acl string
        Upload ACL for S3 Storage (default "public-read")
  -s3-storage-expiration duration
        S3 Storage expiration duration e.g. 24h. Default no expiration

  -gcloud-safe-chars string
        Google Cloud safe characters to be excluded from image key escape
  -gcloud-loader-base-dir string
        Base directory for Google Cloud Loader
  -gcloud-loader-bucket string
        Bucket name for Google Cloud Storage Loader. Enable Google Cloud Loader only if this value present
  -gcloud-loader-path-prefix string
        Base path prefix for Google Cloud Loader
  -gcloud-result-storage-acl string
        Upload ACL for Google Cloud Result Storage
  -gcloud-result-storage-base-dir string
        Base directory for Google Cloud Result Storage
  -gcloud-result-storage-bucket string
        Bucket name for Google Cloud Result Storage. Enable Google Cloud Result Storage only if this value present
  -gcloud-result-storage-expiration duration
        Google Cloud Result Storage expiration duration e.g. 24h. Default no expiration
  -gcloud-result-storage-path-prefix string
        Base path prefix for Google Cloud Result Storage
  -gcloud-storage-acl string
        Upload ACL for Google Cloud Storage
  -gcloud-storage-base-dir string
        Base directory for Google Cloud
  -gcloud-storage-bucket string
        Bucket name for Google Cloud Storage. Enable Google Cloud Storage only if this value present
  -gcloud-storage-expiration duration
        Google Cloud Storage expiration duration e.g. 24h. Default no expiration
  -gcloud-storage-path-prefix string
        Base path prefix for Google Cloud Storage
        
  -vips-max-animation-frames int
        VIPS maximum number of animation frames to be loaded. Set 1 to disable animation, -1 for unlimited
  -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. Set -1 for unlimited (default -1)
  -vips-max-height int
        VIPS max image height
  -vips-max-width int
        VIPS max image width
  -vips-concurrency int
        VIPS concurrency. Set -1 to be the number of CPU cores (default 1)
  -vips-max-cache-files int
        VIPS max cache files
  -vips-max-cache-mem int
        VIPS max cache mem
  -vips-max-cache-size int
        VIPS max cache size
  -vips-mozjpeg
        VIPS enable maximum compression with MozJPEG. Requires mozjpeg to be installed