Tumblr will not allow images with width bigger than 1280.
Any width bigger than 1280 will be resized to fit w1280 automatically,
in which the height of an image will also resized based on width-height ratio.
This is the main reason why I did not use Tumblr in the first time but Imgur instead.
While it is needed to be configured manually to allow high resolution image upload,
Imgur will not resize images into a certain ratio or resolution.
As for Visual Web S,
this is my set from two months ago (August)↓↓
directly from Visual Web S site so the images are not resized
「ビジュアルウェブS」 vol.711 乃木坂46 『ふたりのバカンス』
Maiyan and Ikuchan are featured together,
and I did not want to create separate galleries,
so I hope you will understand the inclusion of Ikuchan in this discussion.
(and also the inclusion of Maiyan in Ikuta discussion, since it is the same gallery)