The Sky Light panel consists of two parts: "Geo and Sky" and "HDRI".
Geo and Sky
Geographic sky can quickly provide natural lighting for interior and exterior scenes.
Simple adjustment
Drag the sun angle control lever to change the time period and the corresponding sun angle. As the sun angle changes, the color of the sky will dynamically change accordingly, showing the light color in the early morning, noon, dusk and other time periods.
Precise Simulation
The geosky system can accurately simulate the real sunlight angle, which is great for project preview and visualization.
Click the ⋮ button to the right of the North Offset to expand the detailed parameter panel.
The default parameter of the geographic sky is the sun angle at 16:00 PM on January 1 in Nanjing, Jiangsu Province (D5 headquarters, 118.8°E, 32°N). Please modify the parameters according to the actual geographic data of your own project in order to get accurate simulation results:
North offset: This parameter is used to correct the direction of "north compass".
Drag the control and the sun's orientation will rotate horizontally. The default value of the control is in the middle, meaning no offset. In the top view, dragging to the right or entering a positive value will rotate the north direction clockwise.
D5 Render will set one of the main axis direction of the model as north. e.g. The positive direction of green axis in SketchUp scene will be recognized as north.
In practical design process, it is usually preferred that the modeling software's axes coincide with the design axes of the building, rather than modeling according to the geographic direction. This means that the axes of most scene files deviate from the geographic north direction, which can be corrected by using the "North Offset" parameter.
If you are not sure where the north direction of the D5 Render is, you can find it according to geographical knowledge. For example, if you set the time to 12:00 noon, the shadow of an object north of the Tropic of Cancer (23.5°N) will then point due north.
Time: Enter parameter as needed.
Date: Enter parameter as needed.
Latitude and longitude: Please enter the real latitude and longitude coordinates of the project.The positive value of the longitude parameter indicates the E longitude, and the negative value indicates the W longitude (parameter range 180°~-180°). The positive value of the latitude parameter indicates N latitude, and the negative value indicates S latitude (parameter range 90°~-90°).
Note that here is Decimal Degree (DD), different from Degree Minute Second (DMS), accurate to one decimal point. Pay attention to the conversion in actual use. For example: 35°30'E should be converted to 35.5°E.
Sunlight Intensity: Adjust the sunlight intensity as needed.
HDRI
Background Knowledge
What is HDRI?
HDRI is the abbreviation of High Dynamic Range Image. Common image formats are hdr, exr, etc. The opposite concept is called "LDRI (Low Dynamic Range Image)". Images in jpeg and png formats are all LDRI.
How can we create an HDRI? Usually, using a camera to capture the same scene at different exposure levels, resulting in several LDR images. Then using specific software, combine LDR information into a single image to obtain an HDR image. Ideally, the pixel values in an HDR image are proportional to the true intensity of light in nature. It records both very bright and very dark information, the so-called "dynamic range" is very high.
HDRI is not only the background, but also illuminates the whole scene.
Why use HDRI?
Here's an example to demonstrate the benefits of HDRI. Open the low and high dynamic versions of the same image in Photoshop and place them together. (HDR image credit: Sunflowers HDRI • Poly Haven).
The upper image is in jpeg format, bit depth: 8 bits/channel. The lower image is in hdr format, bit depth: 32 bits/channel.
By default, both images look the same on the screen, because the bit depth of the screen display is also 8 bits/channel.
Information outside of this range will appear on the screen as "overexposed" pure white, or severely underexposed pure black.
Let's add [Exposure] adjustment layers to both images and lower the exposure level by 3 stops:
The difference is apparent: in the lower HDR image, the areas that were overexposed and turned white show more content: cloud detail, blue sky, sun, etc. The overexposed areas of the LDR image above, on the other hand, simply change from pure white to a dull gray, because no detail was recorded in these overexposed areas in the first place.
We use these two images, as the sky environment background, to render the model, and the difference is also significant:
Differences in sky details:
Differences in reflection details:
Most importantly, the sun in HDRI can cast shadows:
What should I look for when selecting HDRI?
The HDRI environment used in D5 Render are "spherical projection" panoramas. In addition, there are other common panorama projection methods such as cubic and mirror ball.
The spherical projection panorama is characterized by:
- Image aspect ratio is 2:1
- The horizon line is usually at the middle height of the frame.
- The content of the picture can completely cover all angles around the camera.
Here is what a typical HDRI image suitable for D5 Render would look like (compressed to a low dynamic image for web display purposes), and we are going to use this type of image for Sky Light.
(HDR image credit: Sunflowers HDRI • Poly Haven)
Detailed explanation of parameters
Click on the "HDRI" tab and the parameters panel will look like this:
Default HDRI
D5 Render has nine different HDR panoramic environment maps built in for different atmospheres.
Note that the "Pure White" HDRI background will be automatically exposed to gray when the auto exposure option is turned on, so if you want to get a "pure white" background, you need to manually control the exposure.
Customise HDRI
Click "+ Customize HDR" in the drop-down menu to load the hdr file. Supported file formats: hdr, jpg, exr.
Note: Low dynamic range jpg files are also allowed to be loaded here. LDR images can of course provide a reflective background environment and some lighting, just not as realistic as HDR.
Custom imported HDR files are saved to the "customhdr" folder under D5 Render installation path, which can be quickly accessed by clicking on the folder icon to manage custom HDR files.
The "Default" and "Custom" categories can be toggled in the drop-down menu.
Parameter Adjustment
Light: Controls the overall brightness of the HDRI image, thus affecting the lighting of the scene. Note: If auto exposure is turned on, auto exposure will always compensate for changes in overall brightness, making the effect of this parameter less obvious.
Click on the buttons to the right of the Light control to adjust the brightness of the Sky lighting and the brightness of the background respectively:
Skylight: Only affects diffuse lighting. Does not affect material reflections.
Background: adjusts the brightness of the background, and also affects the material reflection.
Rotate: Rotates the HDRI sky environment horizontally, which affects the background content, material reflection environment, and sun azimuth.
Color temperature: affect the color tendency of the sky lighting, affect diffuse lighting, will not affect the background and reflection. The default value is 6500K, lower color temperature will make the diffuse yellowish, higher color temperature will make the diffuse blueish.
Sun
Before we go into the specific parameters, it is important to understand why we need a "sun" feature for the HDRI. The main reason is that not every sun in an HDRI panorama is bright enough to cast realistic shadows.
Only high quality HDRI panoramas that capture enough exposure stops contain enough sun brightness information to produce a clear and realistic shadow. That is, meet the drag-and-drop standard. As the demand increases, more and more HDRI panorama resources are reaching this level.
However, there are still quite a few HDRIs where the sun is not as bright as it needs to be, and the rendered scene will look more like a "cloudy" or "overcast" sky. The shadow is not obvious.
When we turn on the "Sun" switch, D5 Render automatically identifies the brightest point in the HDRI panorama (usually the sun) and adds a solar light source in that direction:
Sunlight intensity: Controls the brightness of the Sunlight source.
Sun Disk Radius: Control the radius of sun disk, it will affect the softness of the shadow edge.
Color Temperature(Sun): affects the color temperature of the sun, The default value is 6500K; lower color temperature will make the sunlight yellowish. You can set a low color temperature for early morning and dusk sunlight. Higher color temperature will make the sunlight blueish.
Direction
- Follow HDRI: Automatically identifies the brightest point in the HDRI (usually the sun) and adds a solar light source at the corresponding location. The advantage is that it usually fits the HDRI environment perfectly, the disadvantage is that the sun's altitude angle cannot be adjusted, and if you want to adjust the sun's azimuth, you need to rotate the HDRI.
- Custom: Disconnecting the solar direction from the HDRI. The advantage is that you can adjust the altitude angle and azimuth angle of the sun freely. The disadvantage is that in certain cases a "double shadow" appears, because there is already a sun in the original HDRI.