Hi Hans and Prabhakar, Hans Verkuil wrote:
Hi Prabhakar! I've got some documentation review comments below... On Thu August 30 2012 00:58:16 Prabhakar Lad wrote:From: Lad, Prabhakar <prabhakar.lad@xxxxxx> add V4L2_CID_DPCM_PREDICTOR control of type menu, which determines the dpcm predictor. The predictor can be either simple or advanced. Signed-off-by: Lad, Prabhakar <prabhakar.lad@xxxxxx> Signed-off-by: Manjunath Hadli <manjunath.hadli@xxxxxx> Cc: Sakari Ailus <sakari.ailus@xxxxxx> Cc: Hans Verkuil <hans.verkuil@xxxxxxxxx> Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx> Cc: Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx> Cc: Hans de Goede <hdegoede@xxxxxxxxxx> Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> --- This patches has one checkpatch warning for line over 80 characters altough it can be avoided I have kept it for consistency. Changes for v2: 1: Added documentaion in controls.xml pointed by Sylwester. 2: Chnaged V4L2_DPCM_PREDICTOR_ADVANCE to V4L2_DPCM_PREDICTOR_ADVANCED pointed by Sakari. Documentation/DocBook/media/v4l/controls.xml | 25 ++++++++++++++++++++++++- drivers/media/v4l2-core/v4l2-ctrls.c | 9 +++++++++ include/linux/videodev2.h | 5 +++++ 3 files changed, 38 insertions(+), 1 deletions(-) diff --git a/Documentation/DocBook/media/v4l/controls.xml b/Documentation/DocBook/media/v4l/controls.xml index 93b9c68..84746d0 100644 --- a/Documentation/DocBook/media/v4l/controls.xml +++ b/Documentation/DocBook/media/v4l/controls.xml @@ -4267,7 +4267,30 @@ interface and may change in the future.</para> pixels / second. </entry> </row> - <row><entry></entry></row> + <row> + <entry spanname="id"><constant>V4L2_CID_DPCM_PREDICTOR</constant></entry> + <entry>menu</entry> + </row> + <row id="v4l2-dpcm-predictor"> + <entry spanname="descr"> DPCM Predictor: depicts what type of prediction + is used simple or advanced.This is not useful information. It basically just rephrases the name of the define without actually telling me anything. I would expect to see here at least the following: - what the DPCM abbreviation stands for - a link or bibliography reference to the relevant standard (if there is any)
There's a Wikipedia article: <URL:http://en.wikipedia.org/wiki/Differential_pulse-code_modulation> It's the same DPCM encoding as in many of the compressed raw bayer formats.
- a high-level explanation of what this do and what the difference is between simple and advanced.
That's somewhat subjective and hardware dependent. If I understand this correctly, the "advanced" should differ only quality-wise from "simple" option. Why one would use "simple" instead of "advanced" then? Perhaps mostly for testing purposes; it might be that the advanced predictor could have issues in certain cases where the simple would not. However this isn't the only piece of hardware where I see that this is configurable, and the simple one was even the default.
If this is part of a video compression standard, then this control would probably belong to the MPEG control class as well.
It's not --- DPCM compression is typically used on the bus between the sensor and the receiver to compress the data as the bus is often a limiting factor in the transfer rate. DPCM compression can be used to squeeze the data from 10 to 8 bits without much loss in quality or dynamic range.
Cheers, -- Sakari Ailus sakari.ailus@xxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
