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Is size of image file important for display speed?

  1. I notice that the html in WordPress for displaying an image is often something like this:

    <img class="size-thumbnail wp-image-59" title="reflection one" src="http://xxxxxxx.wordpress.com/files/2008/10/snv31267.jpg?w=128" border="0" alt="reflection one" width="128" height="96" />

    Does this mean that the full size jpg file (in this case snv31267.jpg (JPEG Image, 2816x2112 pixels)) is sent down from WordPress to the user and the user's browser resizes it to 128 by 96?

    Or does WordPress do it cleverly and store various different sizes of file and send the appropriate one?

    If the former, I will make an effort to reduce images to the maximum size that I make them viewable at.

    Thanks

    The blog I need help with is noticeboards.wordpress.com.

  2. Yes, image size is important for display speed.

    WP stores the file you upload - period. It resizes what is displayed, to the dimensions you specify (up to the maximum allowed for the theme you're using).

    2816x2112 is too large. It's better to upload scaled-down copies of your images, or at least optimized for the web.

    Also note that the WP resizing is less than perfect: you lose some color and sharpness. For a demonstration see here:

    http://en.forums.wordpress.com/topic/pale-pictures?replies=11#post-258262

    So its better to upload images in real size, or of course link to the full-size original.

    Re the last, your latest post has an image that doesn't link to the full-size original when clicked. Perhaps you are unaware of the change since WP2.7. For a linking image, you now have to click "File URL" after uploading and before inserting (you only have to do this once: the uploader will then remember your preference).

    And please paste the exact URL of your blog when asking questions here - or link your nickname to your blog as explained in the Sticky "8 Things to Know". We often need that to give a relevant answer

  3. "Does this mean that the full size jpg file (in this case snv31267.jpg (JPEG Image, 2816x2112 pixels)) is sent down from WordPress to the user and the user's browser resizes it to 128 by 96?"

    No. In this case, WordPress.com resizes the image down to 128 x 96 on the server, then sends the much smaller file to the user's browser.

    (WordPress in general doesn't do this, it's a special WordPress.com feature).

    This will normally happen anytime an image is served from *.files.wordpress.com and the <img> tag includes width and height attributes.

  4. Thanks.

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