我试图在上传到我的服务器之前旋转图像。到目前为止我采取的步骤是:
- 将图像转换为 Base64。
- 使用 Canvas 旋转 base64 字符串。
- 将旋转后的 Base64 转换为图像。
但我无法将其转换回图像格式。最终图像文件(旋转后)无法上传,因为它是一个 blob。
您能否告诉我如何将旋转的 Base64 字符串转换为图像文件,以便我可以创建 blob 并上传它。
我猜我的旋转函数也不正确,因为我尝试转换它并使用转换后的 Base64 字符串在 https://codebeautify.org/base64-to-image-converter 上查看它给了我一个空白文件(黑色图像文件)。
此问题的根源是当用户在 iOS 或 Android 上单击图像并上传时,图像会出现横向。为了解决这个问题,我尝试根据其 EXIF 方向旋转图像。
function detectFiles(event) {
this.getOrientation(event.target.files[0], function (orientation) {
this.imageOrientation = orientation;
}.bind(this));
console.log('the original image data', event.target.files);
this.selectedFiles = event.target.files;
// SAS : Converting the selected image to Base64 for rotation.
const reader = new FileReader();
reader.onloadend = (e) => {
this.base64Data = reader.result;
const rotatedData = this.rotateBase64Image(this.base64Data);
// SAS: Calling the data uri to blob
const selFile = this.dataURItoBlob(rotatedData);
this.uploadFiles(selFile);
}
reader.readAsDataURL(event.target.files[0]);
}
// SAS: Rotate the image.
function rotateBase64Image(base64ImageSrc) {
const canvas = document.createElement('canvas');
const img = new Image();
img.onload = function () {
canvas.width = img.width;
canvas.height = img.height;
console.log('image height and width', canvas.width , canvas.height);
}
img.src = base64ImageSrc;
const context = canvas.getContext('2d');
context.translate((img.width), (img.height));
// context.rotate(180 * (Math.PI / 180));
context.rotate(90);
context.drawImage(img, 0, 0);
console.log(canvas);
console.log('the rotated image', canvas.toDataURL());
return canvas.toDataURL();
}
// SAS: Data URI to Blob
function dataURItoBlob(dataURI) {
// convert base64 to raw binary data held in a string
// doesn't handle URLEncoded DataURIs
const byteString = atob(dataURI.split(',')[1]);
// separate out the mime component
const mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0]
// write the bytes of the string to an ArrayBuffer
const ab = new ArrayBuffer(byteString.length);
// create a view into the buffer
const ia = new Uint8Array(ab);
// set the bytes of the buffer to the correct values
for (let i = 0; i < byteString.length; i++) {
ia[i] = byteString.charCodeAt(i);
}
// write the ArrayBuffer to a blob, and you're done
const blob = new Blob([ab], {type: mimeString});
console.log('the value of the blob', blob);
return blob;
}
此后,我尝试使用以下接受图像文件的函数上传数据。
uploadFiles(selFile) {
// SAS: Setting the 'image uploaded flag' to be retrieved in quick post to prevent duplicate placeholders.
// const file = this.selectedFiles.item(0);
const file = selFile;
this.currentUpload = new Upload(file);
// This is the API call to upload the file.
this.storageApiService.createBlob(file).subscribe((response) => {
console.log(response);
}, (error) => {
console.log(error);
});
}
}
最佳答案
您可以为他们处理 exif 旋转,这样他们就不必旋转图像
我创建了一个库,永远不必使用名为 screw-filereader 的文件读取器额外的好处是,只需调用 blob.image().then(success, failed)
即可轻松从 blob 创建图像,并且它将为您处理图像 exif 旋转。
// unrelevant code (just to get a rotated image with exif metadata)
var exifImage = 'https://cors-anywhere.herokuapp.com/http://duckz.serveblog.net/risorse/foto/francia/P1831_21-02-10.jpg'
fetch(exifImage)
.then(res => res.blob())
.then(blob => {
// just to show the problem you have with your image
const objectURL = URL.createObjectURL(blob)
const img = new Image()
img.src = objectURL
document.body.appendChild(img)
// what screw-filereader can do (auto rotate based on exif data)
// will resolve at img.onload event with a new img element
// will also cast a error if blob isn't a image (img.onerror)
// this is what you need...
blob.image().then(img => {
// convert image back to blob
var canvas = document.createElement('canvas')
canvas.width = img.width
canvas.height = img.height
const ctx = canvas.getContext('2d')
ctx.drawImage(img, 0, 0)
canvas.toBlob(uploadFiles)
// just to show the rotated image
document.body.appendChild(img)
})
})
function uploadFiles(blob) {
// upload blob
}
img {
width: 100px
}
<script src="https://cdn.jsdelivr.net/npm/screw-filereader@1.4.3/index.min.js"></script>
额外提示,使用 canvas.toBlob 而不是使用 dataURItoBlob
关于javascript - Angular4 中的图像旋转,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/48291250/