World HDRi gain

[madcat117]

can you turn up the brightness without making the background image brighter at the same time?

[Sharlybg]

Work mostly with high quality HDRi.
2k or 4k hdri from hdrihaven are good at it.

[kintuX]

can you turn up the brightness without making the background image brighter at the same time?

No.
Also, there's no nodes to play with in World / Environment lighting.
But you could sort of bypass the limitation using one texture for HDRI lighting (Equirectangular/ World) and another (Flat/ Camera, LC Image pipeline) as a Background Image (alike alpha compositing).

[Dade]

Work mostly with high quality HDRi.
2k or 4k hdri from hdrihaven are good at it.

Or convert the HDR image in a PNG or JPEG and use the converted (LDR) image. Than add a sun light source and pick a direction "compatible" with the image shown. At that point you can change the infinite and sun light source gains independently.

[kintuX]

Oh, just remembered an old school trick with Front/Back Opacity node... use a large sphere (or hemisphere, with inverted normals - directed inwards) for background with same texture as is used for HDRI then set Front Op. to 1 and Back to 0.

Hmm, but it looks like not all light is passing through and there's an excessive amount of noise...
i.e.:
Background Opacity @ 1 (HDRI obscured)

Background Opacity @ 0 (HDRI visible)

PS.
After some more tests, i find it quite compromising even with more noise (OIDN does good job at cleaning it out) and less light. It makes sort of natural balance between darker background and stronger HDRI on reflections (otherwise another Env. property should be added - Reflection Texture / ie. check Channels under Image Based Lighting @ Maxwell Render v3 Documentation).