The new "HD photos" option is supposed to increase the pixel limit by 4 times, i.e., 2 times in height and 2 times in width.
The standard limit is 1280 pixels, so the "HD" option should increase the per-side pixel count to 2560.
However, in the Android app, the limit is not 2560 pixels but 2048 pixels.
Additionally, the ability to send photos with a 2560x2560 pixel limit was implemented in the Telegram Desktop client several years ago.
This required enabling the experimental "Send large photos" option.
This option is only needed for sending; other Telegram Desktop or Web users can easily download images with increased resolution.
However, in the Android app, even in the latest version, images with a per-side pixel count higher than 2048 are downloaded in 1280p resolution.
For example, I upload two images via Telegram Desktop: one at 2560x2560 and another at 2048x2048. Any Telegram Desktop/Web user will download these images at 2560x2560 and 2048x2048, respectively.
But in the latest Android app version, the first image is downloaded at 1280x1280 instead of 2560x2560, while the second is downloaded correctly at 2048x2048. In older Android app versions, both images are downloaded at 1280x1280 resolution.
The Android app ignores available image resolutions above 2048 pixels. This is also a bug.
Log in here to report bugs or suggest features. Please enter your phone number in the international format and we will send a confirmation message to your account via Telegram.
(Images are sent in SD quality instead of HD when shared from other apps)