This patch proposes a RFC design to handle blending of various
framebuffers with different color spaces, using the DRM color
properties.
Signed-off-by: Shashank Sharma <shashank.sha...@intel.com>
---
drivers/gpu/drm/rfc-design-blending.txt | 52 +++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)
create mode 100644 drivers/gpu/drm/rfc-design-blending.txt
diff --git a/drivers/gpu/drm/rfc-design-blending.txt
b/drivers/gpu/drm/rfc-design-blending.txt
new file mode 100644
index 0000000..55d96e9
--- /dev/null
+++ b/drivers/gpu/drm/rfc-design-blending.txt
@@ -0,0 +1,52 @@
+Hi all,
+
+I wanted to send this design in a separate thread, but then I realized we can
use this thread itself as many of the
+stakeholders are already active here.
+
+As you all know, we will be dealing with the complex situations of blending of
two(or more) different buffers
+in the pipeline, which are in different format and different color space.
+(PS: This ascii block design is best visible in a widescreen monitor, or in
HTML page)
+
+=====================================================================================================================================================
+
+ property 1 = CSC property 2 = Degamma property 3 =
Gamut property 4 = palette
+ +------------------+ +-------------------+
+------------------+ +-------------------+ RGB REC 2020 buffer
+YUV |color space | |Linearizion | |Gamut
mapping | |Non-Linearizion +-------------------+
+REC709--> |conversion +------->+(Degamma)
+----->+(REC709->REC2020) +-------+(Gamma) | |
+ |(YUV->RGB) | | | |
| | | +------v---------------+
+ +------------------+ +-------------------+
+------------------+ +-------------------+ |
|
+
| |
+
| Blending unit |
+
| |------>
blended output
+RGB REC 2020 buffer (Bypass everything)
| |
+
+--------------------------------------------------------------------------------------------------------------------->
| |
+
| |
+
+----------------------+
+=====================================================================================================================================================
+
+This is a design proposal of a blending pipeline, using a sequence of plane
level DRM properties.
+The description of the block is:
+- Input buffers are two different streams for example
+ - YCBCR buffer in REC709 colorspace
+ - RGB buffer in BT2020 colorspace
+- Aim is to make bending accurate by providing similar input to the blending
unit (same in format as well as color space).
+- Every block here represents a plane level DRM property, with specific task
to do.
+ - first block is CSC property, which is for conversion from YCBCR->RGB
only (This doesnt do gamut mapping)
+ - second block is the property which will linearize the input, a
degamma kind of property
+ - third block is a Gamut mapping proprty, which will do a gamut
conversion (ex 709->2020)
+ - forth block is a Non-Linearizion block, which will apply back the
curve (like Gamma) required
+ - The output of this pipeline is a RGB buffer in REC2020 color space
+ - Any driver can map its HW's plane level color correction capabilities
to these properties.
+ - Once blending is done, driver can apply any post blending CRTC level
color property, to:
+ - Change output type (ex. changing RGB->YUV using CRTC level
CSC property)
+ - Apply a curve on the blended output (using CRTC level
gamma/LUT property)
+
+- Important points:
+ - The sequence of the properties has to be fixed (almost in this
order), considering the linear data requirement of Gamut mapping
+ - The color space of blending needs to be decided in the userspace, by
UI manager, with some policies like (examples):
+ - If any of the buffer is REC2020, all buffers should be
converted into 2020, before blending.
+ - Always blend in Higher/Wider color space.
+ - Always blend in RGB.
+
+- Opens:
+ - Is there a need to communicate HW's capabilities to UI
manager/userspace ?
--
2.7.4
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