Mediawiki Image Resizing - Trying to understand how it works - image

Question

I have Mediawiki 1.21.2 installed. I have also set up ImageMagick on my server and have enabled it in LocalSettings.php. I have already read the Mediawiki's Images manual and I just need to clarify this:
If I am adding a plain image without adding the "thumb" option, will the image be automatically resized for the width I have mentioned or will it only skrink the dimension to that size but still has the original file size? For example, if I using this:
[[File:Sample_Image.jpg|250px]]
In the above statement, I can see that the image will be displayed with the maximum width of 250px. Lets say, if the original image is like 800px X 600px with a file size of 2MB, will the re-sized image for the above dimension will be reduced to only a few KB when the image is reduced to a width of 250px (or) will the image size shown in the article page will still have the original filesize of 2MB but only shrinked to 250px width but doesnt reduce the original filesize? I am just wondering since a lot of my users upload big pictures and these pictures have big file sizes. At the moment, I have added the image like this in my templates:
<div class="main_article_image">[[File:Sample_Image.jpg]]</div>
and then using css, I have minimized the image size like this:
.main_article_image {
max-width: 250px;
height: auto;
}
The current method resizes the images in the articles pages but the file size for these images are still huge and the article page takes too long to load. So I manually resize all images and upload a smaller size for images each time that takes more manual work. Therefore, I am trying to find out if adding the 250px with the image tag like: [[File:Sample_Image.jpg|250px]] will automate this work for me!
I have these settings on my LocalSettings.php for imagemagic:
$wgEnableUploads = true;
$wgGenerateThumbnailOnParse = true;
$wgUseImageMagick = true;
$wgImageMagickConvertCommand = "/usr/local/cpanel/3rdparty/bin/convert";
Can someone please confirm if this will work? Am I doing it the wrong way by resizing it via css? I know adding "thumb" parameter resizes the image, but will it work the same if for plain images without the thumb parameter? If it will, then I need to edit all of my templates and I just want to confirm before I go ahead changing the templates. Anyone who can clarify this will be helpful for me.

Answer 1

Yes, it seems that a smaller image file is generated even without the "thumb" parameter.
For example if you check the help page on images with the example "[[File:Example.jpg|50px]]" and check the url of the small image that is displayed, you'll see that it uses the thumb version /thumb/a/a9/Example.jpg/50px-Example.jpg instead of the full-size version /a/a9/Example.jpg