Difference between reflections and highlights/shadow.

Skills sketching
1

It’s me again! :wink:

I have been asking a lot of questions lately but it’s because I’m trying to “perfect my craft” over the summer, now that classes are out for a bit (gotta keep busy!!). Well, I have been practicing rendering traditionally and digitally and one of the phenomenons that I am still a bit baffled by are reflections and highlights on glossy surfaces.

It took me a while to realize that glossy surfaces react differently to light than matte surfaces (where the surface transition is gradual…thanks to Scott Robertson’s videos on rendering matte surfaces) but when I see a sharp white constrast on a glossy surface, I don’t know if that is the light hitting the object or a reflection of something like a window in the room when the object was photographed. I have been staring at photos of glossy objects in design books and online to decipher how that works and my brain is fried. I can’t figure it out. I just want to better understand so when I render, I can do it convincingly.

From what I understand…matte surfaces don’t show reflections or sharp constrasts, but can someone deconstruct the images of glossy objects I have attached? Which are the reflections and which are highlights from the light source? HELP!! :open_mouth: I know this sounds dumb… but is the “sharp white constrast” demonstrated in these examples of the actual light source illuminating the object or is it a reflection of the window in the room (or surrounding objects reflecting onto the surface)? I hope that makes sense. Thanks guys!

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2

First off, it’s great you’re taking the initiative to learn this necessary skill. It took me a long time to fully understand the concept and wrap my eyes around what I’m seeing…so kudos. Before I begin, do you know that these objects could have been photoshop’d out of the the native background? Or by the reflections, if you look carefully enough, you can make out the photo studio environment.

Second, do you understand the nature of how light affects an object in space and how the light bounces back to your eye? I believe that SR has these diagrams in the DVD if you search from them from your directory folder on DVD. Study these very carefully and keep these diagrams in the back of your head, or at least in front of you. Let me know when you can have the diagrams in front of you, this will make it a bit easier to explain. I would post these, but I believe it’s copywritten, and I don’t want to infringe, plus he was courteous enough to put it in the DVD’s and it’s only fair that he maintains his revenue from the instruction.

Don’t worry about getting it the first time, it will come to you over time and you will master it. Just be vigilant and patient…

3

Yes, those are white diffuser panels used in studio photography. The white square is a piece of thin fabric like material on a frame with a bright light behind it. This is used intentionally to create that white highlight you see in your examples. Look up studio photography setups and you’ll see what I mean.

It could also be a “window” with light coming through it, same idea.

In the digital world, often a small flat plane is created and turned into a lightsource. This plane can be positioned to cast light and also be reflected in glossy surfaces.

This example has a bunch of long white strips:

HDRI map with two rectangular light sources (spherical)

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4

Thanks guys for your feedback. After your replies, I went online and did some research of my own on studio photography and also “specularity” of surfaces… a new word in my vocabulary… :slight_smile:

Masood1224, I actually borrowed those Scott R videos from our on-campus library so I will have to check them out again and look for those files! I never knew there were any. Thanks for mentioning that. It’s too bad that Scott never came out with a “rendering for glossy surfaces” video. The only ones he has so far are for rendering matte surfaces.

Bennybtl, thanks for posting that 3D modelling example and for your explanation too. After spending time online looking at materials and lighting and how they interact and also looking up sites on studio photography, I came to finally make sense of it all!!

Now correct me if I am wrong guys: In the case of the example images I posted… it appears the light source is coming from the right, right? So if these items had all been “matte”, then the highlight would have been a very vague and feathered one and you wouldn’t have seen any sharp reflections at all, because matte surfaces don’t REFLECT anything in the background, right?

The reason these glossy items show that white diffuser panel in their surfaces is because the items are very glossy and it not only shows the light emitting from the light source but it also mirrors in the surface the actual “lighting equipment” used in the photo shoot!! Glossy surfaces, because of their high specularity, show reflections of things that are near it, like a camera, a light bulb from the light source, a table surface, etc?? If these items had been lit up by a single spotlight, then you would have probably seen a white bright speck reflected in the surface instead, right? Because it is reflecting not only the light, but also the actual spotlight far away?

Please tell me I got it right!! It finally ocurred to me that highlights are actually reflections too. I had to separate the actual concept of the light from the “light source” and the “reflections”… if that makes sense. They seem to be independent of one another when it comes to glossy surfaces. The light from the diffuser panel is what is making each item appear brighter on the right side (and the left side a bit darker to create three-dimensionality) but it also is creating a reflection of the actual light source (whether that light source be a diffuser panel or a single bulb), because of the materials reflectivity?

I get really excited when I make what I like to call “breakthroughs”. hehe. Only an ID person would understand me. :slight_smile:

Thanks guys.

5

Let’s take that last image you posted (the orange product). What we can see from it is that there is a main (key) light coming from the right hand side and a fill light (at a lower power) coming from the left hand side, giving a nicely contrasting shape. The key light is also producing that large rectangular specular highlight and also some on the rim of the hole. This is dependant on the angle of the light in relation to the viewer’s eyes. Light bounces off at the same angle that it hits, so light hitting at 10 degrees will leave at 20 (I think I’m right in that but you might want to double check.) A specular highlight is the reflection of the light source.

If you look at the bottom of the product you can see the reflection of the surface the product is sitting on. Even though this is closer to the product than the light source, the reflection is not as bright as there is not the same light energy being ommitted from it as there is from the light. As mentioned, the clean edged reflections are due to the highly glossy surface. What could be defined as a matte surface doesn’t mean that it has no reflective properties or glossiness. But yes the less glossy (the more matte), the softer the reflections.

It’s reflecting the light. If you look into a bright light, all you really see is the light coming out in the shape of the light. That’s what’s being reflected as the specular highlight.

6

Playdo,

Thanks for that explanation. After your posting, I decided to actually go research some studio photography websites and look at how products or items are photographed. I quickly learned about diffuse lighting versus specular lighting and how the material reacts to certain lighting. It then sunk in, what you had said about specular highlights being reflections of the light source!!

Just to clarify, (using the same Orange glossy object as an example) if the light source had been a bright spotlight and not a “soft box” (as what seems to be used in the Orange glossy example), would the specular highlight be a white sharp “dot” on the surface? Or does that also depend on the distance of the light to the object and the material/surface?

Thanks!

7

Yes a spotlight in that case would give a crisp circular highlight, though it could be slightly distorted depending on how much the surface distorts a reflection. The floor reflection is giving off indirect light (light is hitting the floor and bouncing off of it) - that shows you what happens to the highlight, when there is less light is being ommitted from the source. The further you move a spotlight away from a surface, the less light will reach the surface, producing a weaker highlight. If you’ve got a camera or 3d software that lets you play around with specular lighting, it will give you a better understanding.

8

Playdo,

You’ve given me a great idea! I am going to take some photos with my SLR of everyday products lying around my house and light them up with a spotlight and photograph them, to see what actually happens. Maybe that will make it a lot easier to grasp the concept of highlights and reflections. I will photograph products of different materials, from glossy to matte. I will keep you posted what I learn. :slight_smile: Thanks.

9

Check out Scott’s DVD called Industrial Design Rendering - Bicycle. It deals with a lot of glossy surface rendering.

“Scott discusses basic lighting and reflection strategies to indicate a variety of materials and colors.”

10

Reflections: an object that mirrors anything around it. The index of reflectivity is based on its surface and texture- matte, semi- gloss or glossy.
Highlight: the object is reflecting a light source. the highlights can be seen in every surface of the object - fillets, corners, even minute curvatures etc

Reflection and highlights follow the shape of the object- spherical, cylindrical, cubes. For e.g a car- the sides and top are like cubes and reflect and highlight as cube object. The wheel wells are cylinders running perpendicular to the sides. SO when you look at the surface transition from side to wheel wells, the reflection and highlight follow the surface.

Shadow: all object casts a shadow under light.

It is best that you read these differences from real life objects than 3d models. Car’s shows superb reflection, highlight and shadows. In the image i uploaded, there is a whole bunch of reflection from glossy surface, the parting lines have highlights and the ground shows the shadows.
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