Blender School: Photographer 5x

 Photographer 5 (Introduction to lighting)

What is the Photographer addon for Blender?

At its core, Photographer adds rendering, lighting and compositing parameters that are consistent with physical lighting and photography. This is good because it makes setting up and replicating realistic scenes if you are familiar with the many standards used in photography, lighting and optics. Photographer is a must-have if you are marrying Blender outputs to camera footage because you can take your capture parameters, such as exposure and apply them within Blender without doing a stupid amount of conversion work.

There are a lot of additional features, some of which are remarkable. I particularly like the Camera and Lens Post FX because you can set up realistic bloom and glow effects in just a few clicks without needing to access the compositor interface. There are more features, but I've not used them because I've never learned how they work. This blog post documents my journey deeper into Photographer 5.

 First, a refresher on Lighting:

There are two scientific approaches to measuring light:

Photometry: measures visible light by weighting its power according to the human eye's varying sensitivity to different colours. This is a system used by photographers and filmmakers.
Radiometry: measures the total power of light (radiant flux) across the entire electromagnetic spectrum. This is the absolute measure that isn't based on human perception.

Scale and Light
Light strength changes the apparent scale of a scene. This truism should encourage you to set up scenes that use real-world scale, as you are less likely to be bamboozled by trying to make things look realistic that are fundamentally unrealistic. 

Inverse Square Law and brightness
The brightness of a light source follows the inverse square law, so it falls off very quickly. You'll subconsiously see this in any depiction of a real-world scene. 

Example from CGCookie tutorial on lighting.

In the CGCookie tutorial, Jonathan Lampel provides a great example of how a well-crafted 3D scene can compromise realism, as the light from the room's lamps is as bright as sunlight. This would not be the case in reality.

Light intuitions
As an observer with properly functioning eyes, we handle changing light levels extremely well, to the extent that we don't even notice it happening. It makes us poor judges of how much light there is in our environment because the light-capturing equipment in our heads is automatic, and our brain tries to filter the change so we're not distracted from survival tasks.

Blender's built-in light system

Blender uses the energy rating of lamps, measured in watts, to rate light sources. This makes lights easy to understand, but it isn't the whole story. The wattage of a physical bulb is a measure of the electrical energy used to create light. However, traditional bulbs waste a lot of energy in the form of heat, whereas Blender's lights don't simulate poor efficiency; they put all that power out in the form of visible light. The actual output is measured as Radiant Flux (Φ), also measured in watts. If you look at diode or gas discharge lamps, their rating is neither the electrical input (it's actually the equivalent input rating of a traditional bulb) nor the light power. Confusing! Therefore, light power requires a standard unit of measurement. We used Lumens. 

Lumen: the SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela.

This gets more confusing! Different colours of the same light value are perceived differently by human eyes. To measure the value of a naturally produced light, we use a Kelvin value. This is the value of a neutral substance, called a blackbody, that emits when heated to a Kelvin temperature. This is why there's a black body node in Blender. By colouring your lights in Kelvin values, you get more realistic results.

A light's lumen value describes its brightness, while its Kelvin temperature describes its colour.

And it's weirder! Sometimes light is even more complex than that: even with exact temperatures, wattage and so on, an LED lamp will only look like the sun if you stare at it directly, not at the things it illuminates. The full spectrum of an LED lamp is different, and surface materials can respond differently under two seemingly matching lights. There's also polarisation, but that only matters if you want realistic looks through sunglasses; otherwise, adding a bit of colour filtering would be enough to mask its effect.

Kelvin light temperature

Final thing: White Balance.

So this brings together two things we've covered. One, our eyes and brains make numerous adjustments, allowing us to filter out the "cast" created by the colour of light sources and perceive objects as white under standard lighting conditions.

Light sources create a cast based on the Kelvin temperature. From 2000K, we get a warm orange/yellow cast. When we get to 4000K the lighting has a neutral daylight cast, and when we get to the top-end of the range, the light cast turns blue (10,000K). While human eyes and brains do this perceptual filtering, cameras don't. In digital photography, you need to set what white looks like in the environment you are viewing. Professionals often use a white card to calibrate the white balance of their camera, although most cameras have a pretty good automatic setting.

The white balance is not an absolute thing. There are times when you want to capture the colour cast, such as when viewing a sunset, where that quality is an aesthetic element. However, there are times when you need the whites to be white, for example, an interior scene where you want to see that the walls are painted white, not yellow.

White balance controls were introduced as native features in Blender 4.3.