authorProfileImageUrl returns only a tiny thumbnail

Question

I'm trying to use YouTube Data API to get a list of comments for a video.
The problem is that the field authorProfileImageUrl in the response contains a URL to a tiny thumbnail (28x28 pixels) of the profile image instead of the bigger one (48x48) that can be seen in YouTube's comment section. How can I retrieve the bigger one? Am I missing some magic parameter in the request that selects the size of the profile images in comments?

Here's my request URL:

https://www.googleapis.com/youtube/v3/commentThreads?videoId=VIDEO_ID&part=snippet&fields=pageInfo,items(snippet(topLevelComment(id,snippet(authorDisplayName,authorChannelUrl,authorProfileImageUrl,authorChannelId,textDisplay,likeCount,publishedAt)),totalReplyCount))&maxResults=3&key=API_KEY

Edit: Here's an example profile pic URL i get:

https://yt3.ggpht.com/-b-fXZSZ0hPw/AAAAAAAAAAI/AAAAAAAAAAA/mq4JpF46xq4/s28-c-k-no-mo-rj-c0xffffff/photo.jpg
                                                                        ^^

I noticed that the marked part seems to select the size, because when I change the 28 to 48, the size of the profile pic changes too.

I could change it "manually" with some fancy regexp, and it will work, but it will also rely on implementation details that are undocumented and that may change in future and render the application broken :P So it really would be better if there was a documented API way to do that.

Answer 1

Seems like nobody knows how to solve this, ho here's my temporary solution.
It works, but it depends on an implementation detail that can change in the future and then the solution will break apart and will have to be corrected :q

I accept my own answer for now, but when someone posts a better one, I'll accept it instead.

The solution:
I made a simple function that searches for the image size in the URL string and replaces it with a bigger size.

function small2big(url)
{
   return url.replace(/(\/.*s)28(.*\/photo.jpg)$/,"$1"+"48"+"$2");
}

Oh, and here's my middle finger for you, Google: ,,|,,

Answer 2

It seems that actually removing everything right at the 's28' will display the entire image without specifying a size.

For example, instead of this: https://yt3.ggpht.com/-b-fXZSZ0hPw/AAAAAAAAAAI/AAAAAAAAAAA/mq4JpF46xq4/s28-c-k-no-mo-rj-c0xffffff/photo.jpg

You can use this: https://yt3.ggpht.com/-b-fXZSZ0hPw/AAAAAAAAAAI/AAAAAAAAAAA/mq4JpF46xq4/

And it will return the full size image.

In my case, using php I simply:

function bigAvatar($url) {
   $url = substr($url, 0, strpos($url, 's28'));
   return $url;
}

Again, if google decides to change this in the future, this would break. But for now, it works.