[deep__dive]

I make a rendering of a bathroom.



It is lit by emitterplanes and artificial sunlight, reflections come from hdri. I'd like use alpha to put other backgroundimage. But how i can change the reflection in the mirror?

[a.behrens]

I make a rendering of a bathroom.

[img]But how i can change the reflection in the mirror?

Why would you? The mirror shows the reality of your bathroom. So you could change the room for example. Or you could create a frame (maybe with some spotlights) around the mirror the give the mirror plane more substance and make more obviously that there is an mirror. Or you could slightly rotate the mirror so that the mirrored picture shows a different part of the room.

A cheat would be to use a "picture". That means: Create a simple plane and use a material which contains a previously rendered image.

[Bubbaloo]

Render a custom alpha for the mirror.

[deep__dive]

Sorry, i should explain it better. Of course should the mirror show the backside of the bahtroom. But when i change the background in photoshop with alpha, the reflection in the mirror is keep showing the environment of the hdri. i don't have a HDRI from this real place.

when i render a custom alpha, i can change the hole mirror, but i need to change only the environment. the mirror should show the new background, the backside of the bathroom and the reflections on the windows. the mirror should mirroring the alpha, or so...

is there only the way to use a fix hdri image as background and render it, an no possibility to change the background after rendering?

[Bubbaloo]

Ah, interesting situation. Might try rendering with a solid green background (but keep the HDR lighting). Then you can cut out that green BG in Photoshop.

[polynurb]

Ah, interesting situation. Might try rendering with a solid green background (but keep the HDR lighting). Then you can cut out that green BG in Photoshop.

Good idea!!
i'd tend to have hdr in illu+refr+refl. If the rest is emitter based lighting it should give a better result

If it's already rendered i'd say ps+transform would do the job, but this is probably not the right forum to suggest such dirty tricks.