[英]Resizing a image with Javascript without rendering a canvas on the DOM
我在其他许多人中看到了这个有趣的线程: 在不使用画布的情况下在JavaScript中调整Base-64图像的大小
但是,当我使用创建一个屏幕外画布
const canvas = document.createElement('canvas');
结果图像是透明的,大小甚至不匹配参数。 如果我在DOM的画布上画一切都很好
const canvas = document.getElementById('canvas');
这是我的调整大小功能,保持输入图像比例:
resizeImage(file) {
const canvas = document.createElement('canvas');
// const canvas = document.getElementById('canvas');
const context = (<HTMLCanvasElement>canvas).getContext('2d');
// set maximum width and height of output image
const maxW = 400;
const maxH = 400;
const img = new Image;
img.onload = function () {
const iw = img.width;
const ih = img.height;
const scale = Math.min((maxW / iw), (maxH / ih));
const iwScaled = iw * scale;
const ihScaled = ih * scale;
console.log(iwScaled + ' ' + ihScaled);
(<HTMLCanvasElement>canvas).width = iwScaled;
(<HTMLCanvasElement>canvas).height = ihScaled;
context.drawImage(img, 0, 0, iwScaled, ihScaled);
}
img.src = URL.createObjectURL(file);
// retrieve output img in base64 format
console.log((<HTMLCanvasElement>canvas).toDataURL());
}
它从HTML输入中获取文件(File)作为参数。 任何帮助将不胜感激,谢谢。
加载完成后,您将获得Base-64图像。
function resizeImage(file) { var canvas = document.createElement('canvas'); var context = canvas.getContext('2d'); var maxW = 400; var maxH = 400; var img = document.createElement('img'); img.onload = function() { var iw = img.width; var ih = img.height; var scale = Math.min((maxW / iw), (maxH / ih)); var iwScaled = iw * scale; var ihScaled = ih * scale; canvas.width = iwScaled; canvas.height = ihScaled; context.drawImage(img, 0, 0, iwScaled, ihScaled); console.log(canvas.toDataURL()); document.body.innerHTML+=canvas.toDataURL(); } img.src = URL.createObjectURL(file); } document.getElementById("file").addEventListener("change", function() { file = file.files[0]; if (file) { resizeImage(file); } });
<input id="file" type="file">
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