rightimage

rightimage

This module is a small library for streaming dynamic images. Its primary trick is to automatically detect and correct oritentation.

Use

The library exposes a function that can be passed image processing options and will return a stream. We carefully arrange for error propogation and teardown of resources to ensure operation in servers is safe.

const fs = require("fs");
const inputStream = fs.createReadStream("./testdata/test.jpg");

const rightimage = require("rightimage");

rightImage.createRightImagePipeline(
  {
    contentType: "image/jpeg",
    imageOptions: {
      setFormat: 'png',
      resize: "100,100"
    },
    inputStream
  },
  passError(next, pipelineResult => {
    const { outputContentType, outputStream } = pipelineResult;

    const outputFile = fs.writeFileStream("./testdata/output_small.png");
    outputFile.on('close', () => {
      console.log(`wrote ${outputContentType}`);
    })

    outputStream.pipe(outputFile);
  });
);

The example above would take the test JPEG file in the project repository and convert it to a 100x100 PNG write the output "wrote image/png". Since the source JPEG has an orientation, it will be oriented correctly without any further options required.

Implementation

The primary trick is to read the first 128K bytes of the imahe on-the-fly and parse the EXIF data for the image oritentation. We use any present orientation data to calculate the correction required and trigger rotation via image processing libraries. The image data is never buffered.

Image processing

Internally two modules are used to do the core image manipulation work.

express-processimage

This awesome library wraps multiple image libraries - the two invoked by rightimage are sharp and Gifsicle (for the correct conversion of all GIFs including those with animated frames).

We bypass the outer layer that exposes a middleware and instead directly use the internal engine which, based on input options and input content-type, will construct a streaming pipeline that will perform the conversion.

jpegtran

In the case of JPEGs that require nothing more than an orientation change we switch over to the jpegtran library to ensure we make a best effort to best preserve the image quality.

Changelog

v0.2.2 (2019-03-03)

• Tweak title sizes in the README. (Alex J Burke)
• Send coverage data to coveralls and add badge. (Alex J Burke)
• Add comprehensive README. (Alex J Burke)