If the constant-hue factor is not saved, then the R'G'B' image appears as if it were range-compressed. A constant-hue factor, used to restore R'G'B' to the original YUV values, can optionally be stored in the alpha channel.

If the constant-hue algorithm is enabled, the illegal RGB values are converted into legal R'G'B' values. To restore the original YUV image, this correction factor must be saved with the pixel data. The constant-hue algorithm saves the normally lost information in a correction factor that can be stored in the alpha channel. The lost (clipped) information can result in significantly degraded quality when the image is subsequently transformed back to YUV for video output. If the constant-hue block is disabled, then the illegal RGB values are clipped by the output LUT. Because the YUV (YCrCb) color space is a superset of the RGB color space, illegal RGB values can be generated when YUV is converted to RGB. In normal conversion, YUV values that cannot be represented in the RGB color space are clamped or otherwise forced into the legal RGB range. This algorithm allows illegal YUV values to survive a YUV-to-RGB-to-YUV conversion. In addition to the standard color-space conversion model, the Indigo 2 IMPACT Video color-space option provides a constant-hue algorithm. All other controls on the color-space converter node, such as the input, output, and alpha LUTs and matrix coefficients, default to values supporting the specified conversion. These conversions are specified by setting the input and output packing of the color-space converter using the VL_MGV_CSC_INPUT_PACKING and VL_MGV_CSC_OUTPUT_PACKING controls, respectively, and by specifying the input and output ranges using the VL_MGV_CSC_INPUT_RANGE and VL_MGV_CSC_OUTPUT_RANGE. The normal usage of the color-space node is to convert from RGB to YUV/YCrCb or from YUV/YCrCb to RGB color spaces. The kind of the color-space conversion node is VL_CSC its type is VL_INTERNAL its number is VL_MGV_NODE_NUMBER_CSC. The node operates on full-range or limited-range data. The VL_CSC node converts incoming video from one packing to another, where packing describes color space, component encoding, and bits per component, as shown in Table 8-1. Performing Standard Color-Space Conversions This model also shows elements unique to IMPACT Video, such as the constant-hue processing block. The application can use the node's controls to override these values and achieve nonstandard conversions.įigure 8-2 shows a more detailed model of IMPACT Video's color-space converter, including delay blocks synchronizing the component paths. These processing blocks allow the standard RGB-to-YUV and YUV-to-RGB color-space conversions to be implemented, as well as other forms of image processing such as color correction or posterization.īy default, the Video Library's color-space converter node loads standard conversion values for the lookup tables and matrix multiplier, depending on the source and target color spaces. Input lookup tables for each component streamĪn output lookup table for each coefficient streamĪn output block producing pixel/alpha, or dual-linked, streams 4:4:4 to 4:2:2 downsampling is performed for 4:2:2 / 4:2:2:4 output packings You can set the current color depth in lv_conf.h, by setting the LV_COLOR_DEPTH define to 1 (monochrome), 8, 16 or 32.An input block taking in pixel/alpha, or dual-linked, input and producing component streams 4:2:2 -> 4:4:4 upsampling is performed for 4:2:2 / 4:2:2:4 inputs The lv_color_t, lv_color1_t, lv_color8_t, lv_color16_t and lv_color32_t types have four fields: Lv_opa_t A simple uint8_t type to describe opacity. Used to build color arrays from plain numbers. Lv_color_int_t uint8_t, uint16_t or uint32_t depending on color depth setting. Lv_color_t Equal to lv_color1/8/16/24_t depending on current color depth setting Lv_color32_t A structure to store R (8 bit),G (8 bit), B (8 bit) components for 24-bit colors (4 byte) Lv_color16_t A structure to store R (5 bit),G (6 bit),B (5 bit) components for 16-bit colors (2 byte) Lv_color8_t A structure to store R (3 bit),G (3 bit),B (2 bit) components for 8-bit colors (1 byte) Also has R, G, B fields for compatibility but they are always the same value (1 byte) The following variable types are defined by the color module:

8 bit color converter