Light is divided into two categories.
The sun being an extremely intense source of light, most of its rays will reach the ground in a rather directional manner and without their wavelength being affected. This will lead to white light projecting more or less sharp shadows, depending on the visible size of the sun through the atmosphere.
The atmosphere is not a neutral medium (contrary to space) so it shall deflect and spread part of the sunlight and even absorb some wavelengths. During the day, when there is a clear blue sky, the atmosphere will reflect mostly blueish light* that shall tint and soften in a more or less visible manner the shadows drawn by the sun. When the weather is overcast, the clouds block the sunlight and the sun rays are so absorbed and diffuse that only a minor part of the light can reach the ground, from all directions and in a very subdued manner. This will lead to very soft shadows, slightly darker than the better lit parts of the items on the ground.
All such variations in colours and intensity among primary and secondary sources are what makes a sky rich.
And it is that extraordinary dynamic that we have captured by photographing the skies with the largest EVs available on the market.
*At sunset, the angle of the sun in relation to where we stand on the ground forces the light to travel a greater distance through atmosphere to reach our eye. The sun then seems bigger and warm colours prevail.
EVs are a measure unit that allows us to quantify light.
Just like with F-Stop, every time you increase such unit by one EV, you double the intensity of the light. On an HDRi picture, the global number of EVs corresponds by extension to the range between the white point and the black point, i.e. to the difference in brightness between the lightest areas and the darkest areas of such picture...
In reality, certain skies have a great number of EVs. You will have guessed that a clear blue sky in midday sun has a great number of EVs, which is why the shadows are extremely sharp and dark.
An overcast sky however has fewer EVs and shall therefore produce a very soft and uniform light.
What about sunset then?
Paradoxically, sunset can produce a great number of EVs: although the intensity of the sunlight decreases because of the high quantity of ozone it has to go through, the sky is also a lot darker. In other words, the white point is a little less high than during the day but the black point is a lot lower than it would be with a clear blue sky (which, by definition, reflects a lot of light).
EXR is a 32bit float native format that, thanks to the endless colour values it can contain, will allow you to render all the F-Stop registered in shooting time.
It may contain all values between 0 (black point) and 1 (white point) but also values lesser than 0 and greater than 1.
This is why by changing the exposure of our skies, the black and the white both reveal information that could not be seen until then.
HDR has the same technical features but is much heavier and less mainstream than EXR. Also, some software do not perceive the highlights as well in HDR: some whites can turn blue, red, green or even black.
This is why we have decided to deliver our skies in EXR only.
Please feel free to convert them, using software such as Photoshop, if you prefer other formats.
If you happen to hesitate between buying EXR or JPG, remember this:
"HDRi Skies 360" aims at faithfully replicating reality and making it available for video games, advertising, motion pictures and even architectural pre-visualisation.
This is why we have systematically captured all the variations in our skies; from the whitest to the darkest light.
We have photographed the sun down to every detail until total extinction, with enough F-Stop to cover all of its spectrum while removing the visible transitions between different exposures, all of this in very high definition.
That is how we have more than 2,5 more EV than our competitors on skies of an equivalent nature..
Each F-Stop having been captured in shooting time, with "HDRi Skies 360", it is possible to change the exposure without making the HDRi merging transitions visible.
The field of view covered by your camera is about 25°. In this example, your camera therefore covers 25° of 360°, i.e. 7% of the total width of the sky.
If the final render of your HD scene is in 1920x1080, those 25° will correspond to 1920 px (pixels).
To be in a satisfactory definition, our sky should be px=1920/0.07, i.e. 27428 pixels.
This is why all our skies are in 25K.
With HD, the definition required for any 360 sky is huge. Imagine a scene in which you place a camera with a 50 mm focal length :
All our skies have been cleaned up: birds, flares, airplane trails…
And some of our panoramas have been captured at several moments, which allows for light to evolve within a scene.
They can therefore be used in any situation: contemporary or period movie, sci-fi movie, institutional movies, TV shows….
Our skies in JPEG 5K are all free and we have scalable prices until the skies of an optimal resolution and color depth, i.e. the EXR 25K.
Whether you just need an 8bit sky in an average resolution to fit a background or a sky in high resolution and 32bit to light a high resolution 3D scene, you will always find a resolution and a price adjusted to your needs here.