thanks for the scene richy and for getting the matte debate started. i've always struggled to get this to work properly with vray so i hoped corona might make it easier. i was a bit disappointed when i realised there wasn't a proper corona matte shader/workflow to get it working so i was delighted to see richy's posts on this issue. anyway i took richy's scene and tried to get it to work so that there would be no need for an additional corona sun, hoping that the hdri would do all the work - lighting, environment and correct looking (soft) shadows. the benefit of this being that hdri images can be dropped in and out of a scene without having to go back and match up the sun every time you use a different hdri image. i used a trick which i learned from Bertrand Benoit and Peter Guthrie where you adjust the gamma of the hdri image to something less than 1.0 to get sharper, darker, better shadows from the hdri. to do this you have to use the VrayHDRI shader and not the standard Bitmap as richy has used. you then adjust the gamma to get better shadows - Peter Guthrie suggested 0.75 but of course that varies depending on the hdri. in this instance i used 0.50 to try and match the shadows with the shadows cast by the containers in the hdri image. as a result of adjusting the gamma to something so low you then have to use the same hdri image with more normal gamma settings (1.00) for the background image - so for this scene i used one version for the lighting with a gamma of 0.50 and one version for the background with a gamma of 1.00. i then set up a standard CoronaMtl with a CoronaAO map in the diffuse slot and put the background hdri image in the unoccluded slot and applied this to the groud matte material. the Object Properties of this plane were left unchanged.
the first image was rendered using the same exposure and colour mapping settings that richy used but the subsequent images were rendered with my own settings (6500K for example to match more accurately the lighting in the hdri image used). i think the results are not too bad, particularly the quality of the shadows in the mirrored ball reflection which look more like whats actually happening on the ground, however the scene needs more work to better hide the ground plane which can be see very slightly in all of the images, especially the last image.
not sure what happened to the render stamp. any ideas?
very impressed with corona so far.
