have you ever noticed that after you upload an image to your favorite social
media site it sometimes doesn't look quite as good as you thought it would
specifically because the image was compressed or it had its resolution
lowered well naturally it turns out that there are reasons that social media
services do this as it's crucial for helping them manage the millions of
images our selfie addicted society is uploading every day so how exactly do
these large services get images to us quickly and how are they making
improvements to try and keep the image quality as high as they can to answer
that we spoke with nolan o'brien at twitter and we'd like to thank him both
personally as well as twitter itself for help with this episode large services
like twitter face enormous challenges trying to get images to so many
different users the images that go through twitter's servers every day
number in the billions with a b and they have to figure out how to quickly get
them to their 330 million users even if
those users are far away from twitter's data centers a large part of the
solution is using content delivery networks or cdns which are distributed
storage networks that you can learn more about here this way devices will have a
semi-nearby server to pull images from
but what about the images themselves well twitter uses both png and jpeg
images both are compressed which saves bandwidth compared to using huge
uncompressed images that can easily take up around 35 megabytes if shot with a
typical smartphone camera however pngs use lossless compression meaning they're
higher quality but take up significantly more space than a jpeg typically twitter
will convert most images to jpeg if the png version has a high color depth
meaning that if they support 16 bit or a little over 65 000 colors which actually
isn't all that many considering modern displays support millions of colors
additionally jpegs that take up more than five megabytes are also reduced in
quality but hold on a second i use twitter all the time and i think the
images look pretty decent how do they pull that off using so much compression
keep in mind that twitter still supports jpegs up to about 16.7 megapixels or
about 4.2 megapixels if you're uploading from mobile
and when the service has to reduce to jpeg quality it does so by only about 15
percent typically such a loss in quality isn't noticeable unless you're looking very
closely yet still saves a significant amount of bandwidth and this is
especially true since phone screens these days are very high resolution yet
small in size so images can very easily be scaled down in resolution without a
noticeable loss in visual fidelity many phone screens only have one red or blue
pixel for every green so trying to show a super high resolution photo on them
would be a waste as the phones can't even reproduce them accurately if you
compare these images to original side by side on a high res desktop monitor you
may notice a difference but for phone users who are often most impacted by
speed constraints the compression methods we've mentioned so far are no
brainers of course sometimes noticeable trade-offs even on mobile devices cannot
be avoided many people use social media services without fast connections so if
you're on a slow connection you might notice that twitter uses progressive
jpegs meaning that a low quality version will fully load first while you wait for
the higher res version contrasting with the slowly loading image from top down
as you probably remember from the dial up era if you're old then you have to
factor in how people use many different devices including some really old ones
this is a big part of the reason you might have noticed that twitter header
images often appear to be lower quality as they're capped at 500 pixels
vertically to ensure that they can be shown correctly on legacy devices
but what about all the space these pictures take up on twitter's servers
well it turns out that storage isn't all that difficult to expand so the choices
that social networks make with how they process images has less to do with drive
capacity and more to do with how to use
as little bandwidth as possible for the end user after all who has an extra five
seconds to wait for the next zesty Linus beam to load am i right not me check out
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