SPRUIV7B May 2022 – September 2023 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP
The overlay manager supports two color transparency modes - source and destination. These modes cannot be active at the same time.
The source transparency is tied to the top most layer, so the layer to have this transparency applied to has to be mapped to the highest z-ordered input (layer-1) of the overlay manager. The destination transparency is tied to the bottom most layer, so the layer to have this transparency applied to has to be mapped to the lowest z-ordered input (layer-0) of the overlay manager.
The source and destination transparencies are defined as following:
The transparency color key is enabled via the DSS0_OVR_CONFIG[10] TCKLCDENABLE register bit.
The minimum transparency color values are specified in the TRANSCOLORKEY field of the DSS0_OVR_TRANS_COLOR_MIN and DSS0_OVR_TRANS_COLOR_MIN2 registers.
The maximum transparency color values are specified in the TRANSCOLORKEY field of the DSS0_OVR_TRANS_COLOR_MAX and DSS0_OVR_TRANS_COLOR_MAX2 registers.
The transparency color key values defined in the registers are compared with the pixel values. If each color component (R, G, and B) is in the range defined by MIN and MAX, then there is a match. If at least one of the color component is not in the range, then there is no match.
The values of the source transparency color key define the range of encoded pixel data considered as a transparent pixel. The encoded pixel values with the source color key value inside the valid range are not visible, and the encoded pixel values of the under layers or solid background color are visible.
The source transparency color key can be used with YUV and RGB formats (ARGB, RGB, RGBA, xRGB, and RGBx). In that case the A information is ignored for the comparison between the pixel value and the color key value. It is possible to use YUV formats with some care, since the comparison is between the input pixel value of the overlay manager from pipeline and the color key value. The YUV data is converted to RGB format. The user must consider the color space conversion processing in order to define the RGB color key value used for the comparison, in case the original format is YUV.
The scaler can be enabled as a preprocessor in the video pipelines. The pixel scaling processing can be considered in order to define the color key value to be used after the rescaling for the comparison between the input pixel value to the overlay manager and the color key value.
The source transparency color key mode is selected by setting the DSS0_OVR_CONFIG[11] TCKLCDSELECTION register bit to 0x1.
Figure 12-509 shows an example of source transparency color key usage. The pixels with the transparency color key are not displayed. Instead, pixels of the resulting layer underneath are shown.
The destination transparency color key values define the range of the encoded pixels in layer-0 (bottom layer), which are not going to be displayed. That is, the encoded pixel values matching the destination color key value range are pixels not visible on the screen. Pixels at the same position in the layers above layer-0 are visible. The destination transparency color key is applicable in the layer in the background only when there is an overlap between the layer in background position and the layer just above it, otherwise, the destination transparency color key is ignored. See Section 12.9.1.4.1.9.2, DISPC Overlay Mechanism, for details on layer position depending on the Z-order parameter.
The destination transparency color key can be used only with RGB formats (ARGB, RGB, xRGB, RGBA, and RGBx). In that case the A information is ignored for the comparison between the pixel value and the color key value. It is possible to use YUV formats with some care since the comparison is between the input pixel value of the overlay manager from pipeline and the color key value. The YUV data is converted to RGB format. The user must consider the color space conversion processing in order to define the RGB color key value used for the comparison in case the original format is YUV.
The scaler can be enabled as a preprocessor in the pipelines. The pixel scaling processing must be considered in order to define the color key value to be used after rescaling for the comparison between the input pixel value to the overlay manager and the color key value.
The source transparency color key mode is selected by setting the DSS0_OVR_CONFIG[11] TCKLCDSELECTION register bit to 0x0.
Figure 12-510 shows an example of the destination color key usage. The pixels from layer-0 (bottom layer) equal to the transparency color key are not displayed and are replaced by the pixels from layer-1 (top layer). All other layer-0 pixels, different from the transparency color key, are displayed over layer-1.