您可以使用以下代码预览选定的图像

<ngx-dropzone-image-preview ngProjectAs="ngx-dropzone-preview" *ngFor="let f of files" [file]="f" [removable]="true" (removed)="onRemove(f)">
</ngx-dropzone-image-preview>

如果还想显示标签

<ngx-dropzone-image-preview ngProjectAs="ngx-dropzone-preview" *ngFor="let f of files" [file]="f" [removable]="true" (removed)="onRemove(f)">
        <ngx-dropzone-label>{{ f.name }} ({{ f.type }})</ngx-dropzone-label>
    </ngx-dropzone-image-preview>

I understand your question.I was facing the same issue.For this, you have 
to have a blob response. So if you have a url you have to convert it into a 
blob response. I have given an example below

URL: string = `https://fireflysemantics.github.io/i/service-parts- 
help/electrocardiogram-36732.png`;
files: File[] = [];

this.loadImage().subscribe(i => {
  const myFile = new File([i], this.URL, {
  type: i.type,
 });
 this.files.push(myFile)
})

loadImage(): Observable < Blob > {
 return this.http.get(this.URL, {
  responseType: "blob"
 });
}