Image transparency replaced with checkerboard on zoom

[shidarin]

A PNG image with transparency is respected on the preview image within the chat stream:

But not in the zoomed view:

Where the transparency is replaced with a checkerboard.

Because of the checkerboard background, I figure there's a chance this was already discussed, and is intentional behavior. If so, this issue can be closed.

[shidarin]

Apparently this is only the case when Pan & Zoom is disabled. Turning Pan & Zoom to enabled causes the transparency to be respected.

[zulipbot]

Hello @zulip/server-misc members, this issue was labeled with the area: uploads label, so you may want to check it out!

[Anupam-dagar]

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[Anupam-dagar]

@shidarin what should be the expected behaviour?
is it to show background color instead of checkerboard?

[shidarin]

That was my expected behavior- display the image over the background color while respecting transparency.

I initially thought that the checkerboard was a concious design decision, but it goes away when you click the pan & zoom button. That makes me think it's a bug.

[Anupam-dagar]

so what change should be done?

[shidarin]

I would determine what's causing the checkerboard to appear, then adjust that to be the background color instead.

[ghost]

Discussed this a bit with @timabbott in #issues:

Some pertinent bits:

Tim Abbott: It seems like it's clearly a bug that they are different between the two views. How we want to resolve it is a bit ambiguous. I think we originally did the checkboard thing so that it's clear if you have a transparent image that it is transparent (otherwise, you might think it has a blue background, which could be confusing).

Tim Abbott: So I suspect we'd be happier to flip it to always due the blue background, but I'd be interested in others' thoughts.

So, anyone have any thoughts on checkboard vs the blue background?

[Anupam-dagar]

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[aero31aero]

My concern here would be in cases where a transparent png is made up of mainly blue color. The checkerboard design helps in eliminating most of such cases due to its frequent and consistent changes, so worst case, it is like looking at an image through a net, but the image is still visible.

[timabbott]

I think the current thinking is we will eventually want to make the background controllable by an option.

[Anupam-dagar]

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[zulipbot]

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[shidarin]

Posted an update for the wrong issue. Ignore this.