shadow catcher

[celmar]

hello! I have a little annoying problem: with a shadow catcher shot, and a set of backplate + hdri, I can't put -4 in the exposure, because the background image is much too dark... if I set the exposure back to 1, the only values I can use with the sun or the hdri are very low, 0.1 for example... There are not many latitudes... Is there a way around this problem?

[houska]

Hello!

If I understand correctly, you should have a look at the Corona Tonemap Control shader. It allows you to select, which post-processing effects will be applied to the shader. In its default settings, all post-processing effects are disabled, so to solve your issue, you just have to add the Tonemap Control shader into the self-illumination slot of the backplate material and insert your HDRI image as a subshader of the Tonemap Control shader.

[celmar]

hello!!!   mmmm, I'm sorry, Houska, I'm afraid I didn't understand your answer! when using a plane with a shadowcatcher material, you have (in the combo hdri+ backplate) a jpg on the shadow catcher plane. the same jpg on a material which is dropped in the corona "environnement override", and, of course, a corona sky with the hdri linked...   If I set up the tone mapping at exposure: -4, I can have the full range of the gap, with the sky and the corona sun... But the backplate picture is very dark; If I use an exposure of 1, the sun is nearly too strong, even at 0,1.. But the backplate picture is normally lighted...  I don't understand how to "add the tonemap control shader into the self illumination slot of the backplate material"...  ???
   Thank you for some explanations, Houska!!!

[TomG]

Like here - you load the HDRI into the tonemap, the defaults (highlighted in red) are to have all VFB effects off, then in this case I put the tonemap into a Corona Light material onto a plane (which we'll pretend is the backplate). You can see that even though exposure is set to -10 in the VFB, this has no effect on the backplate image (one note, if you do change exposure etc. in the VFB, then you have to restart Interactive Rendering or normal rendering to restore the "unaffected" version of the backplate image).