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A few reasons:

1) Although the site serves up images at 1024 pixels (or whatever) today, in the future they may want larger images. When everyone is rocking 10K monitors and 6K phone displays, those small images are going to look pretty bad.

2) The original image has some metadata that they want to keep (geolocation, etc).

3) They think they can do a better and more consistent job resizing than the various browsers, which is probably true.

agree on 3) most browsers just use linear interpolation when resizing images, which makes sense from a performance point of view, but looks terrible. Better to use a bi-linear or cubic resize, more computing up front, but better images, this is probably the reason they do it

But soon you can do any type of resizing through WASM on the browser.

You can already do it, just use a library or implement your own scaling function and don't use the built-in image resize functions.

This is my understanding as well, you could kill a browser trying to do single-threaded bilinear or cubic resize on a sufficiently large image.

bi-linear is linear interpolation

I think they may have meant "nearest-neighbor", which isn't true for any browsers that I know of.

Regardless, there are still better filters than bilinear, i.e. Lanczos, which I'm pretty sure none of the browsers use.

If you resize the image in steps, with each resize at least 50% of the previous step, you can do a pretty decent approximation of cubic resize using the canvas. Doing this for a year now, we've gotten no complaints and we have designers as clients :)

> 2) The original image has some metadata that they want to keep (geolocation, etc).

Isn't exif data something you should strip out?

Discord makes most of their revenue from selling user data so they probably want to keep as much as possible.

Do you have a source? That's a pretty bold claim, and I haven't seen anything else to back that up.

pretty sure they've directly stated that they're not selling user data

to be fair, you could say the same of facebook/google. they're not selling the data (giving it to third parties), but they're making money off it.

Sure, they serve said data to other authorized users and clients (intended recipients). Name a business that doesn’t do that. ;)

point is, their statement does not preclude them from using data for marketing purposes. some people are content with that, but others take it as a sign that they are (or will) use the data to build dossiers on users.

Our site would have been happy with full res images from the start. As it is now we are stuck with 80x80 images that needs replacing with higher res images since the originals was not kept in any sorted order.

So you kept the originals, but didn't organize them into a way you could use them later?

Long story but from the start we kept originals organized. Then we restructured and the new people couldnt care less and threw away originals or left them named 1,2,3 and so on. All useless now.

This is for proxying images that users link in chat, not for when users upload images to the service. It doesn't make sense to talk about doing this resize on the client, as the client doesn't have the image.

That is a great point. It could still be feasible to cache the image on the client, and have it do the resize. Although I probably wouldn't accept it as a client, especially if my internet cuts out halfway through.

Yes, the use-case of proxying images is a different mater. I was talking about client uploads since so many companies seem determined to waste my bandwidth and time uploading without resizing first.

Client uploads with client-provided thumbnails could lead to some pranks.

You know, a thumbnail with a cute kitten but something completely different after you click on it ;)

I think you misunderstood. The client is uploading a single data blob for each image, but the blob can be smaller if the client resizes it first.

As mentioned in the post, one of our core product features is preventing your IP from being shared. Given that requirement, images shared in chat have to be proxied through our infrastructure. When doing this we save a lot of money and improve client performance by reducing image sizes.

So why the image can't first be resized/compressed before being sent through your infrastructure...?

Ah sorry I misunderstood you. We keep the original image around and provide different sizes for different platforms/resolutions/dpis/etc.

There's no reason this couldn't be a two-step process, resizing to something reasonable on the client then fine-tuning it on the server. I'm presuming you don't see the need to start with multi-megapixel images.

> I'm presuming you don't see the need to start with multi-megapixel images.

Might be a fair presumption today, but might not be for the future with hiDPI screens, VR etc... for the relative storage costs, it'd be better to have the original, and then you can programmatically run from there.

Today's hiDPI screens can already display more detail than your eye can perceive. The issue wasn't about storage costs, it was about transmission costs which still matter for the foreseeable future.

Perhaps, but I think you can compress current-day phone images considerably without losing any actual image fidelity (because the sensor pitch significantly exceeds the lens resolution, and .. noise).

You should seriously consider doing this for your mobile client; the worst thing about Discord is that it eats mobile data if you're uploading lots of images.

That’s exactly the reason why the iOS Mail app asks you whether you want to attach an image in small/medium/large/original size.

Data aside, my phone takes pictures at ridiculously high resolutions. Whenever I go to send pictures with discord, it takes a good 30 seconds and half the time it'll just break.

As an aside, I wish the "share" button would share a lower resolution image instead. I don't mind storing the full quality picture, but handling a 10mb image is seriously silly.

The other side of this is if you're on mobile data and they decide to resize the images on the client then people will complain about the app eating up battery life because it's using so much CPU to resize the images. Plus, they won't have the full size image to share with people you may be chatting with on desktop. If you want to not use so much data while uploading images then you should probably resize them yourself or just not upload images unless you're on wifi.

From the notes of your link:

"drawImage() will ignore all EXIF metadata in images, including the Orientation. This behavior is espacially troublesome on iOS devices. You should detect the Orientation yourself and use rotate() to make it right. "

If the origin of the image is the client and you got the client side resize wrong, then you might introduce artifacts when trying to fix it on the server because the data loss. Also if clients are mobile, you might like to optimize the battery of clients instead of computing time on the server.

Even several years ago there were libraries on github that accounted for iOS defects. However, that aside, just skip the resize on iOS and send as-is. The server still has to verify the result anyway.

The question now is, what drains more power, sending the image and resizing it before sending. If the user has a good WiFi or 4G connection, sending the file as it, should be quicker and more energy efficient. With a 2G or 3G connection, uploading a photograph can take significantly longer (1min on poor/average 3G, which means the antenna is working for that duration and draws a lot of battery). Converting it should not take more then a second. Furthermore, I would prefer using less data then using a tiny amount of battery.

First: Please don't use "Edit" for responding to responses to your comment; it make following threads much, much harder.

On Topic:

> Some people mention having original highest-resolution images are important. I don't think that is true for most applications.

It is true for every application when the next generation of displays hits the market. The question is not the long term usability of our current low-res images but just the migration to the next step. At the moment Acorn announces their new APhone and has a million handsets sold by tomorrow, you want your service to deliver at least viewable images. It's not always the app that sets the bar, sometimes it is the device.

Edit: As someone who travels rather remote places of this planet regularly I'm grateful for every app that does not put the burden on the client. My battery packs only last so long.

The last thing I want is client-side image resizing when my browser is already choking on heavy javascript.

These images are often links from the web or posted by a bot, so they're not on a client until after they've been served.

As I understand they needed to download images from any external servers using an URL. I am not sure if that is possible even with CORS.

Also they don't save preview images and generate them when needed as I understood. So what you are suggesting requires a lot of disk space to keep thumbnails that might be never needed later.

And if you don't have millions of uploads per day then it makes no sense trying to save some seconds of CPU time by unnecessarily complicating the system. In most languages there already are libraries for resizing images.

I have no idea how what you are saying related to compressing images before they are sent?

Many do resizing initially, but even when resizing, you still need to resize images for different reasons, such as thumbnails. So what you need to do is resize on client as low as you are willing to go, and then upload that. But you still need to resize for different needs. You don't want the client doing multiple resizes and uploads for that.

Because then you don't get to build out fun infrastructure like this and write it up in your company blog.

Sure you do! Don't you know that adding "Free" to a title increases the ROI by 40%?

"How Discord Resizes 150M Images Every Day for Free"

Agreed. I wish the posts contained a "it cost X developer hours to recreate thumbor or $$$ total, and we saved Y dollars per month" meaning in approximately 15 years we'll have broken even on this investment. Oh yeah and we don't even do intelligent resizing like thumbor does.

It looks like thumbor is built on a Python stack similar to what Discord was using in their original service. What makes you say they didn't consider it or benchmark it against their previous service and make the decision that it wasn't as good as they needed?

It may work in certain cases.

But it also means you need to know how you will display when you save it. Layout changes, screens change, how do you anticipate the future dimensions / resolution you will need out of the original?

Historically, resizing images client side doesn't work because most clients are not able to render the images, let alone resize them.

The image file formats are very very complicated, many are platform specific, some are covered by patents.

For example of a common issue, another comment mentioned the rotation parameter, it's set by many cameras but the support is inconsistent.

You often want the original because different clients may display different sizes.

isn't it a meme at this point, pushing computational work to the client side? I have a laptop or mobile device, please don't hog my limited cpu and battery life by forcing my device to resize images.

Are you sure your wifi connection will not eat more power with huge upload than processor/gpu doing the scaling?

I dont see how that matters at all.

also -- there's also page load time. if it's an intensive calculation then the overhead of sending the results over http is still less than the browser calc time.

Mandatory XKCD: https://xkcd.com/1683/

Imgur does this.