<p>The charts you show aren't showing two different phenomena - "glossy reflection" and "specular reflection" - they're showing two parameters of specular reflection. One is the <em>specularity</em> or <em>specular colour</em> and gives the amount or brightness of the specular reflection. The other is the <em>glossiness</em> or <em>roughness</em> and shows how sharp the specular reflection is.</p>

<p>Put another way, if you picture the curve of the specular reflection over changing angle, the specularity (the vertical axis on your charts) gives the height of the peak - the maximum brightness - and the glossiness gives the width of the peak - the size of the highlight. The highlight gets narrower with increasing glossiness, whereas roughness is the inverse of this.</p>

<p><em>BRDF</em> is more general: it's a function that tells you how much light is reflected in a given direction (view direction) from a given direction (light direction). Usually (for most materials) we approximate a BRDF using a <em>diffuse term</em> and a <em>specular term</em>.</p>

CC BY-SA 3.0
2017-08-10T03:56:54.830Z
What's the difference between the two different phenomena - "glossy reflection" and "specular reflection"?
chaosink
CC BY-SA 3.0
2017-08-10T03:58:40.957Z
I found another image.
chaosink
CC BY-SA 3.0
2017-08-10T08:42:29.773Z
There **aren't** two different phenomena. That's exactly what I just explained. Your third image is no different from the original two: it's just showing what effect the glossiness parameter has on the specular highlights.
Dan Hulme
CC BY-SA 3.0
2017-08-10T13:02:48.353Z
I misunderstood your words...
chaosink
CC BY-SA 3.0
2017-08-21T14:27:55.467Z
_The amount or brightness of the specular reflection_ - this is also called metalness, right?
mdkdy
CC BY-SA 3.0
2017-08-22T07:36:59.323Z
@narthex No, that's something different. You should ask a new question.
Dan Hulme
CC BY-SA 3.0
2017-08-09T14:22:33.817Z
2017-08-09T14:22:33.817Z
Dan Hulme
<p>Gloss and Specularity are features of the surface. In modern PBR terms we usually refer to the smoothness and metalness of a surface instead (unless you use a specular workflow, then metalness is still linked to specular).</p>

<p>Basically, dielectric surfaces reflect around 4% of light in a specular way, and the rest is diffuse. Metallic surfaces reflect no light diffused, and all specular. Specular light bounces directly back to the eye and shows clear reflections of the environment more. Diffuse bounces around a lot more and therefore gives a more matte result. Gloss is another term for smoothness of a surface. When a surface is rougher its specular light is bounced all over, and so the reflection appears more blurry.</p>

<p>TL;DR: Specular is how shiny it is and usually is higher with metals. Gloss is how clear the reflections are.</p>

<p>Keep in mind that there are some surfaces that don't fall into the metalness workflow, especially when they have a coat on top. There are also materials in between metal and dielectric (semiconductors / metalloids).</p>

CC BY-SA 3.0
2017-08-16T15:27:36.590Z
2017-08-16T15:27:36.590Z
Karim Abdel Hamid
<p>I've noticed a lot of confusion in the use of terminology in this field, sometimes also scientific papers or software packages misuse these words, I agree with @gallickgunner explanation.</p>
<p>To sum up and from my understanding:</p>
<ul>
<li><p>materials have diffuse and specular reflection only.</p>
</li>
<li><p>in dielectric, you have both (and for physically based workflow they should never exceed 100%). If you have a certain amount of specular reflection you will have an inversely proportional amount of diffuse reflection and vice versa.</p>
</li>
<li><p>diffuse reflection is the light that scatters right underneath the surface and is reflected in all directions (diffuse reflection can be imagined as the base colour of the material or albedo), a material that has only the diffuse component looks flat and matte (like a very rough plaster), however, no materials in the world have only diffuse reflections.</p>
</li>
<li><p>the specular reflection is the light reflected on the surface of the material and can be sharp or blurry</p>
</li>
<li><p>the amount of blurriness of specular reflection is controlled by the glossiness parameter (or its inverse the roughness parameter)</p>
</li>
<li><p>for materials like metals the diffuse component is 0% and the specular is 100%, however, for coloured metals like gold or copper, the colour is given to the specular reflections and not to the diffuse reflections</p>
</li>
<li><p>a material that has 100% specular reflection with 100% glossiness, and 0% diffuse reflections it's a mirror</p>
</li>
<li><p>a material that has 100% specular reflection with 0% glossiness and 0% diffuse reflections looks like a very rough metal (like a heavily sandblasted silver) however, metals in real life always have some amount of glossiness it's never 0%</p>
</li>
<li><p>the &quot;specularity&quot; parameter is usually used to &quot;weight&quot; the % of specular reflection</p>
</li>
<li><p>the &quot;specular colour&quot; parameter is used to assign the colour to the specular reflections (metals and other strange hybrid materials can have coloured reflections; non-metallic/dielectric materials usually have white specular reflections)</p>
</li>
<li><p>the diffuse reflection might not always has a weighting factor as the specular reflections, usually it is controlled by the luminosity of its colour.</p>
</li>
<li><p>the &quot;diffuse colour&quot; parameter is the same as the specular colour but assigns a colour to the diffuse reflections rather than the specular ones.</p>
</li>
</ul>
<p>Additional observations:</p>
<ul>
<li><p>the metalness does not describe a different type of reflection, but it basically makes sure that when increasing the specular reflections, the diffuse reflections are lowered proportionally. (so basically, when you increase specular reflections to 100%, even if there is a colour assigned to the diffuse colour channel you won't see it because it would be weighted down to 0%)</p>
</li>
<li><p>Do not mistake the diffuse reflection with the subsurface scattering (SSS), the SSS is an effect that scatters the light underneath the surface as the Diffuse, but it can go way farther underneath the surface compared to the diffuse, in theory, if you set the SSS distance to a very low number you could replicate the Diffuse reflection effect, however, it is much heavier to calculate, so when you don't need to go very far beneath the surface you just avoid calculating it and you rely only on the diffuse effect.</p>
</li>
</ul>

CC BY-SA 4.0
2023-02-23T11:46:50.183Z
2023-02-24T14:40:48.100Z
2023-02-24T14:40:48.100Z
rikkarlo
<p>In the book Computer Graphics Principles and Practice, they use the term specular reflection when they want to imagine things resembling a mirror and glossy reflection when things like a polished door knob or an orange skin.</p>

<p>The charts shows you exactly that. When a material has more specular color, it should have less diffuse color due to the conservation of energy. That is, the sum of the light reflected specularly and light absorbed and emitted in random directions must be less than equal to 100% (the amount of light incident on the surface). Hence when you increase the specular color the material tends to go white or have a slight tint of the color like in metals. </p>

<p>Where as glossy surfaces can have more diffuse color but show a specular highlight like the surface of an orange skin.</p>

<p>So assuming the CGPP's point of view, we can say in pure specular reflection, the diffuse part is much less than the glossy part. Where as in glossy reflection the diffuse part is usually greater.</p>

CC BY-SA 3.0
2017-08-09T17:13:25.293Z
I think CGPP uses "specular" for sharp, mirror-like reflection due to a perfectly smooth surface, and "glossy" for blurred reflection due to a rough surface. I don't think that distinction has anything to do with the specular color or energy conservation. It sounds like you might be mixing this up with metallic vs dielectric materials (metallic = high specular with no diffuse; dielectric = low specular + diffuse).
Nathan Reed
CC BY-SA 3.0
2017-08-09T18:14:20.863Z
no i know that, i wrote all that on the basis of CGPP's assumption. That's one way to think of it. what you said "dielectric = low specular + diffuse" that's what cgpp is referring to as glossy.
gallickgunner
CC BY-SA 3.0
2017-08-09T18:20:32.777Z
No, dielectric != glossy. Glossy just means a blurry reflection due to a rough surface. Metals can have glossy or sharp reflection, and dielectrics can have glossy or sharp reflection. They're two independent axes of variation.
Nathan Reed
CC BY-SA 3.0
2017-08-09T19:29:56.147Z
I think i am bad at explaining and you are getting me wrong. I never said dielectric == glossy. What i mean is, dielectrics can be glossy if they have a specular componenet like you mentioned. I don't understand what do you mean by metals having "sharp or glossy" reflections. Reflection is either diffuse or specular or atleast that's what i have read in all different places. Glossiness or specular highlights is an effect of specular reflection.
gallickgunner
CC BY-SA 3.0
2017-08-10T06:14:19.213Z
https://en.wikipedia.org/wiki/Gloss_(optics)
chaosink
CC BY-SA 3.0
2017-08-10T06:54:17.083Z
@chaosink - ? like i am saying there is no such thing as glossy reflection. Gloss is an effect due to specular reflection. Specular reflection is the correct word. The other type is the diffuse reflection. You can think of gloss as how much the light is reflected specularly. The higher the amount the more glossy the surface.
gallickgunner
CC BY-SA 3.0
2017-08-09T15:55:00.263Z
2017-08-09T16:02:45.520Z
2017-08-09T16:02:45.520Z
gallickgunner
<p>What is the difference between glossy and specular reflection?</p>

<p>What is their relations with BRDF?</p>

<p><a href="https://i.sstatic.net/mqALR.jpg" rel="noreferrer"><img src="https://i.sstatic.net/mqALR.jpg" alt="enter image description here"></a>
<a href="https://i.sstatic.net/ic1g1.jpg" rel="noreferrer"><img src="https://i.sstatic.net/ic1g1.jpg" alt="enter image description here"></a>
<a href="https://i.sstatic.net/gIaQ5.png" rel="noreferrer"><img src="https://i.sstatic.net/gIaQ5.png" alt="enter image description here"></a></p>

<brdf><reflection><specular><material>
What is the difference between glossy and specular reflection?
chaosink
# What is the difference between glossy and specular reflection?

(Asked by: username_0 on 2017-08-09)

What is the difference between glossy and specular reflection?

What is their relations with BRDF?

[![enter image description here](https://i.sstatic.net/mqALR.jpg)](https://i.sstatic.net/mqALR.jpg)
[![enter image description here](https://i.sstatic.net/ic1g1.jpg)](https://i.sstatic.net/ic1g1.jpg)
[![enter image description here](https://i.sstatic.net/gIaQ5.png)](https://i.sstatic.net/gIaQ5.png)

**Tags:** brdf, reflection, specular, material


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## 4 answers

### Answer by username_1 on 2017-08-09. Score: 7

The charts you show aren't showing two different phenomena - "glossy reflection" and "specular reflection" - they're showing two parameters of specular reflection. One is the *specularity* or *specular colour* and gives the amount or brightness of the specular reflection. The other is the *glossiness* or *roughness* and shows how sharp the specular reflection is.

Put another way, if you picture the curve of the specular reflection over changing angle, the specularity (the vertical axis on your charts) gives the height of the peak - the maximum brightness - and the glossiness gives the width of the peak - the size of the highlight. The highlight gets narrower with increasing glossiness, whereas roughness is the inverse of this.

*BRDF* is more general: it's a function that tells you how much light is reflected in a given direction (view direction) from a given direction (light direction). Usually (for most materials) we approximate a BRDF using a *diffuse term* and a *specular term*.

> **Comments:**
> **username_0**: What's the difference between the two different phenomena - "glossy reflection" and "specular reflection"?  
> **username_0**: I found another image.  
> **username_1**: There **aren't** two different phenomena. That's exactly what I just explained. Your third image is no different from the original two: it's just showing what effect the glossiness parameter has on the specular highlights.  
> **username_0**: I misunderstood your words...  
> **username_2**: _The amount or brightness of the specular reflection_ - this is also called metalness, right?  
> **username_1**: @narthex No, that's something different. You should ask a new question.  

---

### Answer by username_3 on 2017-08-16. Score: 3

Gloss and Specularity are features of the surface. In modern PBR terms we usually refer to the smoothness and metalness of a surface instead (unless you use a specular workflow, then metalness is still linked to specular).

Basically, dielectric surfaces reflect around 4% of light in a specular way, and the rest is diffuse. Metallic surfaces reflect no light diffused, and all specular. Specular light bounces directly back to the eye and shows clear reflections of the environment more. Diffuse bounces around a lot more and therefore gives a more matte result. Gloss is another term for smoothness of a surface. When a surface is rougher its specular light is bounced all over, and so the reflection appears more blurry.

TL;DR: Specular is how shiny it is and usually is higher with metals. Gloss is how clear the reflections are.

Keep in mind that there are some surfaces that don't fall into the metalness workflow, especially when they have a coat on top. There are also materials in between metal and dielectric (semiconductors / metalloids).


---

### Answer by username_4 on 2023-02-23. Score: 1

I've noticed a lot of confusion in the use of terminology in this field, sometimes also scientific papers or software packages misuse these words, I agree with @username_5 explanation.

To sum up and from my understanding:

* materials have diffuse and specular reflection only.
* in dielectric, you have both (and for physically based workflow they should never exceed 100%). If you have a certain amount of specular reflection you will have an inversely proportional amount of diffuse reflection and vice versa.
* diffuse reflection is the light that scatters right underneath the surface and is reflected in all directions (diffuse reflection can be imagined as the base colour of the material or albedo), a material that has only the diffuse component looks flat and matte (like a very rough plaster), however, no materials in the world have only diffuse reflections.
* the specular reflection is the light reflected on the surface of the material and can be sharp or blurry
* the amount of blurriness of specular reflection is controlled by the glossiness parameter (or its inverse the roughness parameter)
* for materials like metals the diffuse component is 0% and the specular is 100%, however, for coloured metals like gold or copper, the colour is given to the specular reflections and not to the diffuse reflections
* a material that has 100% specular reflection with 100% glossiness, and 0% diffuse reflections it's a mirror
* a material that has 100% specular reflection with 0% glossiness and 0% diffuse reflections looks like a very rough metal (like a heavily sandblasted silver) however, metals in real life always have some amount of glossiness it's never 0%
* the "specularity" parameter is usually used to "weight" the % of specular reflection
* the "specular colour" parameter is used to assign the colour to the specular reflections (metals and other strange hybrid materials can have coloured reflections; non-metallic/dielectric materials usually have white specular reflections)
* the diffuse reflection might not always has a weighting factor as the specular reflections, usually it is controlled by the luminosity of its colour.
* the "diffuse colour" parameter is the same as the specular colour but assigns a colour to the diffuse reflections rather than the specular ones.

Additional observations:

* the metalness does not describe a different type of reflection, but it basically makes sure that when increasing the specular reflections, the diffuse reflections are lowered proportionally. (so basically, when you increase specular reflections to 100%, even if there is a colour assigned to the diffuse colour channel you won't see it because it would be weighted down to 0%)
* Do not mistake the diffuse reflection with the subsurface scattering (SSS), the SSS is an effect that scatters the light underneath the surface as the Diffuse, but it can go way farther underneath the surface compared to the diffuse, in theory, if you set the SSS distance to a very low number you could replicate the Diffuse reflection effect, however, it is much heavier to calculate, so when you don't need to go very far beneath the surface you just avoid calculating it and you rely only on the diffuse effect.


---

### Answer by username_5 on 2017-08-09. Score: 0

In the book Computer Graphics Principles and Practice, they use the term specular reflection when they want to imagine things resembling a mirror and glossy reflection when things like a polished door knob or an orange skin.

The charts shows you exactly that. When a material has more specular color, it should have less diffuse color due to the conservation of energy. That is, the sum of the light reflected specularly and light absorbed and emitted in random directions must be less than equal to 100% (the amount of light incident on the surface). Hence when you increase the specular color the material tends to go white or have a slight tint of the color like in metals.

Where as glossy surfaces can have more diffuse color but show a specular highlight like the surface of an orange skin.

So assuming the CGPP's point of view, we can say in pure specular reflection, the diffuse part is much less than the glossy part. Where as in glossy reflection the diffuse part is usually greater.

> **Comments:**
> **username_6**: I think CGPP uses "specular" for sharp, mirror-like reflection due to a perfectly smooth surface, and "glossy" for blurred reflection due to a rough surface. I don't think that distinction has anything to do with the specular color or energy conservation. It sounds like you might be mixing this up with metallic vs dielectric materials (metallic = high specular with no diffuse; dielectric = low specular + diffuse).  
> **username_5**: no i know that, i wrote all that on the basis of CGPP's assumption. That's one way to think of it. what you said "dielectric = low specular + diffuse" that's what cgpp is referring to as glossy.  
> **username_6**: No, dielectric != glossy. Glossy just means a blurry reflection due to a rough surface. Metals can have glossy or sharp reflection, and dielectrics can have glossy or sharp reflection. They're two independent axes of variation.  
> **username_5**: I think i am bad at explaining and you are getting me wrong. I never said dielectric == glossy. What i mean is, dielectrics can be glossy if they have a specular componenet like you mentioned. I don't understand what do you mean by metals having "sharp or glossy" reflections. Reflection is either diffuse or specular or atleast that's what i have read in all different places. Glossiness or specular highlights is an effect of specular reflection.  
> **username_0**: https://en.wikipedia.org/wiki/Gloss_(optics)  
> **username_5**: @username_0 - ? like i am saying there is no such thing as glossy reflection. Gloss is an effect due to specular reflection. Specular reflection is the correct word. The other type is the diffuse reflection. You can think of gloss as how much the light is reflected specularly. The higher the amount the more glossy the surface.  

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