High Bit Depth Rendering with VPixx Devices

Starting from version 1.10, you may choose to render in high bit depth directly in LabMaestro. This process is automated and will adjust your stimuli to the selected mode. Depending on the VPixx device used, the total resolution (10 bits, 12 bits, etc.) will vary according to your device type.

Changing Video Mode in LabMaestro

Directly for Each VPixx Device

By clicking on your VPixx hardware in the Project window, under the Environment tab, you can access the device properties. In the Video section, you can select the required video mode for your experiment.

Through Timeline Properties (Preferred Way)

Another option is to specify a rendering mode for the experiment timeline. The rendering mode defined for a specific timeline overrides the one defined in device properties, making it useful if you need to change rendering modes between timelines during the experiment. To do so, you must first check the Overriding Rendering Mode box in your timeline’s properties (double-click on the timeline to access its properties). In the properties, select the preferred rendering mode.

Rendering Modes

High Bit Depth Grayscale (M16)

The high-bit-depth grayscale rendering mode enables VPixx hardware to display grayscale stimuli with greater precision, albeit at the expense of color rendering. High-bit-depth is achieved by combining the 8-bit red and green color channels into a single 16-bit grayscale-only channel. This mode is compatible with all supported screen resolutions. As such, high-bit-depth grayscale rendering can be instrumental when running experiments that benefit from higher precision in gray levels but do not utilize colored stimuli. The remaining 8 bits of the blue colour channel may be optionally used to index a user-defined 256 x 3 CLUT containing 16-bit RGB pixel values. Images assigned to a row in this table will be drawn in the designated colour as an overlay on the main grayscale image.

For more information on the inner workings of M16 rendering, please visit the vocal guide on this mode.

High Bit Depth Grayscale Demo

Download the LM project demo here: M16RenderingDemo.lm

The M16RenderingDemo displays two ramps: one going from black (0) to gray (0.5) and the other from gray (0.5) to black (0). The top ramp uses 16-bit values to define shades of gray, while the bottom ramp uses simulated 8-bit values. Running this demo in the default rendering mode reveals no difference between the two ramps. However, when run using high-bit-depth grayscale rendering, it becomes apparent that the top ramp is much more precise than the bottom ramp. The difference is evident in the larger quantization of the bottom ramp compared to the top one, as 8-bit rendering allows only 2⁸ possible shades of gray, whereas 16-bit rendering allows for up to 2¹⁶ shades of gray. Depending on your display, fewer values may be available (for instance, the PROPixx can render 2¹² shades of gray).

High Bit Depth Half Width (C48)

High Bit Depth Half Width rendering enables VPixx hardware to expand the range of displayed color levels for all three color channels (red, green, and blue) by increasing the possible values from 2⁸ to up to 2¹⁶. This mode comes at the cost of half of the display’s horizontal resolution (e.g., 1920x1080 becomes 960x1080). High Bit Depth Half Width rendering can be beneficial when better color precision is required and high resolution is not necessary.

For more information on the inner workings of C48 rendering, please see the vocal guide on this mode.

High Bit Depth Half Width Demo

Download the LM project demo here: C48DemoMulticoloured4.lm

The High Bit Depth Half Width demo displays two ramps. The top one showcases the increased precision of the High Bit Depth Half Width rendering mode, and the bottom one shows standard rendering. As the demo is built for use with the PROPixx, the precision of the top ramp is 12-bit (2¹² color values). The bottom ramp will display larger quantization, as the color precision is lower. Four ramps are shown, starting with the red channel, then green, blue, and grayscale. If you override the display rendering back to its default mode, no differences will be observable between the two ramps.