pnx1500 NXP Semiconductors, pnx1500 Datasheet - Page 372

• Manufacturer Part Number: pnx1500
• Description: Pnx15xx Series Connected Media Processor
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Volume 1 of 1
PNX15XX_SER_3
Product data sheet
Figure 6:
Current Pixel Extracted Alpha
Pixel Formatter Block
Previous Alpha
Previous Pixel
Mixer Block Diagram—Pixel Processing
New Pixel
Alpha_REG
2.6.2 Alpha Blending
2.7 Output Pipeline Structure
Alpha
Blending allows video and graphics to be combined with varying levels of
transparency. Blending is possible only when both current and previous Layer pixels
are valid. Either 16 or 256 levels of blend from one layer to another and vice versa are
available. The blend value may come from a layer’s alpha register or from the upper 4
or 8 bits of an incoming pixel or is a multiplication of both.
The blending is done according to the following equation:
Pixel_result = alpha x Pixel_current + (1-alpha) x Pixel_previous
Pre-multiplied pixel formats are supported. The Premult bit is set, which means the
incoming pixel stream is already pre-multiplied with the per-pixel alpha value. The
resulting alpha blend equation is as follows:
Pixel_result = Pixel_current + (1-alpha) x Pixel_previous
An additional per-component pre-multiply with a constant can be achieved by proper
programming of the color space matrix. Fading of alpha values is controlled by the
alpha_mix bit. If it is set, the pixel alpha gets multiplied by the fixed alpha value/256.
Remark: Alpha=255 has the effect, in hardware, of making alpha equal to 1 in the
above equations.
The input to the output pipeline comes from the mixers. The output pipeline houses
the formatter (FRMT) that produces the final output stream in the required output
format.
Invert_ROP
Rev. 3 — 17 March 2006
premult
Alpha_Use_REG
Alpha
Blend
Alpha_Pass_ROP
Alpha_ROP
Select_ROP
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Valid Pixel?
PNX15xx Series
next MIXER Stage
Previous Alpha for
Chapter 11: QVCP
New Mixed Pixel
11-19