Luminance material channel

[IKHandel]

Hi guys

Perhaps you can help me with this odd rendering problem

Using C4D 11.5 with latest win 32bit patch. I use AR3 for Rendering.

I believe that the luminance material channel is where I place a texture that will not be further affected by any lights in the scene. This is good.

BUT

I have a standard (not HDRI) photo of a street with good lighting that I am using in the luminance channel as a projection, using projection man.

I project the photo onto some basic cubes and planes made editable. In the view window it all projects really well. The view looks exactly the same as the photo including the colour, contrast, light areas and shadows and pixel resolution. Identical to photo so far, this is good!

The problem is when I render the scene everything is much much darker than the photo??
There are no lights in the scene as I believe with luminance channel material they are not required?

I CAN brighten the render using the picture viewer filters and render gamma, although it is difficult to get EXACTLY the same as origonal photo .

My question is, why is it darker at all, when I thought the idea of luminance channel is to use texture (Photo) as it's own brightness? Is there a way to get the same brightness as the projected texture shows in the perspective view window, in a render? Why is there a difference? Should there be a difference in the viewport display and the render, or am I doing something wrong?

IK

[wega]

Hi IK mmm...it's so strange because usually the luminance channel give to the material the same light as the photo attached into...can you post a viewport screen shot and render screenshot? (you can attach directly into the topic)

Can you insert a material manager window open to see the luminance channel?

Have you some post effects into render settings switched on as color mapping?
It never heppen to me with luminance channel, because it don't be affect from other lights into the scene...it's very strange

W

[masterzone]

As said by Wega, can you show us the Projection man window opened?

Mz :D

[IKHandel]

I will grab some screen captures and post in next couple of hours.

One thing meantime... this seems specific to projection man. Luminance renders normally if I just paste a photo in luminance channel onto a UV'd object and no projection man. I scratch my head

IK

[masterzone]

ah ok...but have you put picture into projection Man "L" channel ?

mz

[Arkimed]

Hi IKHandle,
the problem is in the alpha channel.

The picture in the luminance channel is displayed properly, but if the alpha is not appropriate, generates a semi transparent image .

Consequently, the image is darker because it really shows the black background.

Arkimed

[IKHandel]

Hi Arkimed.. thanks for your reply.

I have luminance channel and alpha channel generated by projection man (PM) and both channels show up in the PM window. I am using the new projection/load bitmap option as I already have the origonal photo. I check PM channels and both are set as backgound layer and all projected Luminance and alpha channels are highlighted orange (active) in the PM manager.

The screen capure shows alpha channel for right building projection, as automatically made. Bottom right the alpha settings as set by PM for projection.

Comparing shadow areas of projection and final render as you say it is the dark areas that are incorrect, but what should I do differently to fix alpha?

IK
PS I know using projection with shadows is a bad idea, I am just using this photo to learn the projection process. The manual is a bit basic to learn this process well.

[wega]

argh, I don't think that this is a good alpha channel . I don't know PM, but from where did you generated the alpha?

W

[Arkimed]

If you use the function "Load Bitmap" in PM, you have to disable the alpha channel, unless you upload an image that has an alpha channel created ad hoc, or PM using the RGB image as alpha channel and it's not good.

Once you create the material with only the Luminance channel, go again in PM window and right-click the object in question (the one with the material you just created) and this time choose Render Coverage ...

This will render the scene and the image will be loaded automatically in Photoshop (or bodypaint, depends on the preferences you set).

In Photoshop, create a new layer on which to paint the details you want and save the image again.

At this point you will have your C4D object with a new material that will have the picture painted in the luminance channel and an alpha channel automatically generated during the previous trial.

It 'easier to understand trying it, rather than to explain it in words.

Arkimed

[IKHandel]

Ok thanks for that. Having been testing since my last post and found out about deleting alphas.
Not quite sure why this is required but at least progress has been made.

I'll follow you workflow in another test and see how it goes.

Many thanks for you help!

Do you know of any indepth tuts for projection man, I can't find any that are not VERY basic?

IK