Pasted images are twice bigger when GNOME is scaled 200%

smartptr

Hello,

Let's set GNOME scale to 200%, take a screenshot with PrtSc, and paste here:

The image is shown bigger (scaled 200%) than the original.

Now let's set the scale to 100%:

Thanks?

smartptr

Yeah, so when Gnome scale is 200%, the screenshots are twice bigger

smartptr

Same with Firefox, by the way, and electron apps.
When pasted to GIMP, though, the image is fine.

yojimbo274064400

If display resolution is 1920 × 1280 then a screenshot would produce an image of 1920 × 1280 regardless of GNOME's scaling, i.e. screenshot at scale of 100% or 200% both produce images equal to the display resolution.

smartptr

The display resolution is 3840x2160, with 200% GNOME interface scale. Uploaded image is scaled by some reason. I don't quite understand at what step the image becomes twice bigger.
I noticed in youtube stats for nerds the viewport is in lower resolution with scaling (1920x1080*2.00 when running on 4K fullscreen). Might be this happens to canvas as well, or whatever is processing the pasted image.

smartptr

Browsers follow the environment scale, so they scale font and all media. Therefore, the original screenshot of a scaled interface gets scaled again.
The solution is to make use of the image DPI, I guess, which must be set when making a screenshot, so that browsers could display it accordingly.

Basically, an image of a 10 cm² size should be presented as 10 cm² on any screen and any interface scale (not talking about browser specific page zoom).

yojimbo274064400

Sorry but I cannot reproduce this issue; maybe lack of understanding it on my par. Hopefully someone will be able to understand the issue and help.

DoctorG

@smartptr No DPI calculation can be done as GNOME screenshot tool dose not store any resolution in the PNG file.

DoctorG

@smartptr said in Pasted images are twice bigger when GNOME is scaled 200%:

Basically, an image of a 10 cm² size should be presented as 10 cm² on any screen and any interface scale (not talking about browser specific page zoom).

A browser is not a Desktop Publishing app. What you want, scaling by screen resolution, zoom and image resolution was never added as a webstandard.
You can only trust your DTP or Image editing app that it will display correct.

smartptr

@DoctorG Even if GNOME screenshot did add the resolution, it wouldn't help. I tried to set different DPI to the same image, and it doesn't change the appearance on the screen. I made images with 300 and 600 DPI in their EXIF, and it didn't change anything.

A browser is not a Desktop Publishing app.

I can only partially agree with you. Nowadays, people do everything in browsers, even edit documents for printing. That would be unfortunate to not being able to insert an image of precise real-world dimensions to a page you edit. But, even on Google Docs, where I would expect my images to be displayed properly, it won't work.
Such an oversight!

DoctorG

@smartptr said in Pasted images are twice bigger when GNOME is scaled 200%:

I can only partially agree with you. Nowadays, people do everything in browsers, even edit documents for printing.

May be users do, but they do expect wrong, a browser is not the new MS Word which can do everything correct.
Unfortunately users sometimes do not recognise restrictions of browsers.

smartptr

Right, and not right. Browsers' job is to display marked-up documents with media. There is nothing, except the lack of agreement (aka standards) and will, which would prevent browsers to take DPI (or rather PPI) into account.
The information is right there in the image, take it and do the right calculations, which is a bit tricky part, as there's page scale, different screen resolutions and scale, which must be provided to the browser correctly.

DoctorG

@smartptr If dpi and zooms is not respected for images with such information, it is a browser bug when it does not display in correct size.

Interesting article ⇒ https://web.dev/articles/high-dpi?hl=en

smartptr

As far as I understood, and you told me above, the browsers basically ignore DPI set in the EXIF, and treat them as they're all at 72.

No difference between Firefox and Vivaldi.

No DPI:

Screenshot from 2024-01-05 18-03-04.png

300 DPI:

Screenshot from 2024-01-05 18-03-04-300dpi.png

600 DPI:

Screenshot from 2024-01-05 18-03-04-600dpi.png

DoctorG

@smartptr said in Pasted images are twice bigger when GNOME is scaled 200%:

treat them as they're all at 72.

As i remember that was more, 96 ppi.

DoctorG

@smartptr Yes, browser renders images in pixel width/height of current device, does not use a print output device resolution.

smartptr

I went ahead, created a page with

<hr style="width:1000px;height:10px;border-width:0;color:gray;background-color:gray">

And measured the bar with a ruler. It gave me 310 mm. Meaning 1000px/310mm = 1000px/12.2in ≈ 82 PPI, ahhaha.
Those 1000px are displayed on a 4K screen with 3840 pixels width with 200% scale as 2000px.

Then, this 1 inch bar:

<hr style="width:1in;height:10px;border-width:0;color:gray;background-color:gray">

Gave me 1.18 inches long (not 200% bigger!). This means the screen PPI is communicated, but slightly less than actual. So if I add the 1.18 correction to 82 PPI, it gives 82×1.18 ≈ 96 PPI.

So although not ideal, but even with 200% screen scale, the browser have some idea about PPI, but doesn't apply it to images.

There is actually this image-resolution CSS property that's going to change the world, but it is still experimental, and not supported by anybody yet.

smartptr

I checked the EDID sent by the display, and it is not correct, apparently:

Name: LG ULTRAFINE
EISA ID: GSM5bc2
EDID version: 1.4
EDID extension blocks: 1
Screen size: 70.0 cm x 40.0 cm (31.74 inches, aspect ratio 16/9 = 1.78)

While the actual size is about 60 cm, hence the 1.18 error. Such a shame.

DoctorG

@smartptr Now, was the wrong EDID the cause for images not showing up correct on your GNOME?

smartptr

@DoctorG , no, it only adds a little error. The main problem is that image resolution is not taken into account by the browsers.

P.S. The EDID v1.4, which is communicated by my display, only allows 1 byte to set the screen size in centimeters (1 byte width + 1 byte height). So I cannot set it to my actual 59.6×34.1 cm. I'll see if I can do anything with that, like overriding the data with another EDID format and udev rules.