how to compress a base64 image to custom size

Question

I send/receive my image by using base64. I have a base64 string and I want to compress it to my size.

for example I want to reduce photo size to 100kb.

Is it possible?

Solution

This was a fun challenge cuz it involved a binary search until it finds the right size. I'm not going to advice you to solve this with base64 instead of blob cuz you should really handle it as binary (blob) otherwise it takes up ~33% more data as base64

This code includes resizing that you can set a max width/hight and still be able to keep the aspect ratio and auto quality lookup until it finds the correct quality to match the MAX_SIZE

console.log('Downloading lorem ipsum image to simulate a file from user input')

fetch('https://picsum.photos/1920/1080/?random')
.then(res => res.blob())
.then(blob => {
  const img = new Image()
  img.src = URL.createObjectURL(blob)

  console.log(`Original image size (at 1920x1080) is: ${blob.size} bytes`)
  console.log('URL to original image:', img.src)
  
  img.onload = () => resize(img, 'jpeg').then(blob => {
    console.log('Final blob size', blob.size)
    console.log('Final blob url:', URL.createObjectURL(blob))

    console.log('\nNow with webp\n')

    resize(img, 'webp').then(blob => {
      console.log('Final blob size', blob.size)
      console.log('Final blob url:', URL.createObjectURL(blob))
    })
  })
}) 


const MAX_WIDTH = 1280
const MAX_HEIGHT = 720
const MAX_SIZE = 100000 // 100kb

async function resize(img, type = 'jpeg') {
  const canvas = document.createElement('canvas')
  const ctx = canvas.getContext('2d')
  
  ctx.drawImage(img, 0, 0)
  
  let width = img.width
  let height = img.height
  let start = 0
  let end = 1
  let last, accepted, blob
  
  // keep portration
  if (width > height) {
    if (width > MAX_WIDTH) {
      height *= MAX_WIDTH / width
      width = MAX_WIDTH
    }
  } else {
    if (height > MAX_HEIGHT) {
      width *= MAX_HEIGHT / height
      height = MAX_HEIGHT
    }
  }
  canvas.width = width
  canvas.height = height
  console.log('Scaling image down to max 1280x720 while keeping aspect ratio')
  ctx.drawImage(img, 0, 0, width, height)
  
  accepted = blob = await new Promise(rs => canvas.toBlob(rs, 'image/'+type, 1))
  
  if (blob.size < MAX_SIZE) {
    console.log('No quality change needed')
    return blob
  } else {
    console.log(`Image size after scaling ${blob.size} bytes`)
    console.log('Image sample after resizeing with losseless compression:', URL.createObjectURL(blob))
  }
  
  // Binary search for the right size
  while (true) {
    const mid = Math.round( ((start + end) / 2) * 100 ) / 100
    if (mid === last) break
    last = mid
    blob = await new Promise(rs => canvas.toBlob(rs, 'image/'+type, mid))
        console.log(`Quality set to ${mid} gave a Blob size of ${blob.size} bytes`)
    if (blob.size > MAX_SIZE) { end = mid }
    if (blob.size < MAX_SIZE) { start = mid; accepted = blob }
  }

  return accepted
}

PS/warning Canvas don't do any good compression, if you paint a jpg picture on a canvas element and get the image back with no resizing, manipulation quality loss or changing the format toBlob('image/jpg', cb, 1) then you will most definitely get a larger file back since they probably already are well compressed and canvas dose none. I only change the quality & max width/height to reduce the size with the canvas api. You would need some compressor to reduce it even more without quality loss.

• jsfiddle demonstration of file increase with canvas
• imageoptim
• squoosh.app
• zopfli
• pngcrush

Comments

[Ben]

Decode it to an image format, set it to a canvas, then encode it using PNG or jpg to the target size, then encode as base64.

[Prashant Pimpale]

Using javascript or any serverside lang?

[Ben]

Possible duplicate of How to compress an image via Javascript in the browser?

[Hyyan Abo Fakher]

Possible duplicate of JavaScript reduce the size and quality of image with based64 encoded code

[Endless]

if you don't encode it as base64 you will save ~3x more in size

[Venugopal M]

Exactly the question I wanted to ask !

[Endless]

ps, if you change to image/webp you get a lower quality loss

[siddharth shah]

thanks for the wonderful answer. It would be even great if you are able to attach a working example!!

[siddharth shah]

In while loop blob is not getting generated. it is null

[Venugopal M]

Worked in a jiffy! Exactly what I was trying to figure out for a couple of weeks. BTW, I just ignored the "webp" part and it gave me a size of 170Kb instead of 900 !