压缩图片大小JavaScript

Question

I am doing project where we can take snap shots from video. You can view my code snippet below.

             function snapshot(){
                context.drawImage(video, 0, 0, w, h);
                img = document.createElement("img");
                img.src = canvas.toDataURL();
             }

w,h are nothing but width and height of video. Those are calculated as shown below.

            video.addEventListener('loadedmetadata', function() {

               var ratio = video.videoWidth / video.videoHeight;
               w = video.videoWidth - 100;
               h = parseInt(w / ratio, 10);
               w= w-100; h= h-100;
               canvas.width = w;
               canvas.height = h;           
            }, false);

The base64 Image I am getting here is approximately 260kb. I want to reduce this image to below 80kb.

I tried using canvas.toDataURL('image/png', 0.2) but no use.

Answer 1

The quality setting is only valid when the type of image is either jpeg or webp . Try using the following:

canvas.toDataURL("image/jpeg", 0.1);

For example, from the Docs :

A Number between 0 and 1 indicating image quality if the requested type is image/jpeg or image/webp .
If this argument is anything else, the default value for image quality is used. Other arguments are ignored.

Answer 2

The specification and MDN say that the second argument is not supported for PNG images. The specification says the second argument is just for image/jpeg ; MDN says image/jpeg or image/webp .

Note that browsers are not required to support anything other than PNG, and if you request something they don't support, they give back PNG. So you can do:

img.src = canvas.toDataURL('image/jpeg', 0.2);

...and you'll either get a JPEG low quality ( 0.2 is really low), or a PNG ignoring the second argument.