1. 选择一张图片
const img_original = document.getElementById('img_original');
const img_output = document.getElementById('img_output');
let blob;
function preview(file) {
let reader = new FileReader();
reader.onload = function () {
img_original.src = this.result;
img_original.onload = () => {
console.log('图片原始宽高:', img_original.naturalWidth, img_original.naturalHeight);
console.log('图片原始大小:', file.size)
}
};
reader.readAsDataURL(file);
}
2. 使用Canvas压缩
function compress() {
// 压缩到图片原始宽高的一半
let w = img_original.naturalWidth / 2;
let h = img_original.naturalHeight / 2;
let canvas = document.createElement('canvas');
let ctx = canvas.getContext('2d');
let anw = document.createAttribute("width");
anw.nodeValue = w;
let anh = document.createAttribute("height");
anh.nodeValue = h;
canvas.setAttributeNode(anw);
canvas.setAttributeNode(anh);
ctx.fillRect(0, 0, w, h);
ctx.drawImage(img_original, 0, 0, w, h);
const base64 = canvas.toDataURL('image/jpeg', 0.75);// 压缩后质量
const bytes = window.atob(base64.split(',')[1]);
const ab = new ArrayBuffer(bytes.length);
const ia = new Uint8Array(ab);
for (let i = 0; i < bytes.length; i++) {
ia[i] = bytes.charCodeAt(i);
}
blob = new Blob([ab], {type: 'image/jpeg'});
console.log('压缩后的图片大小', blob.size);
// 预览压缩后的图片
img_output.src = base64
}
3. 保存到本地
function save() {
if (blob) {
let a = document.createElement('a');
let event = new MouseEvent('click');
a.download = Math.round(new Date() / 1000) + '.jpg';
a.href = URL.createObjectURL(blob);
a.dispatchEvent(event)
}
}
