Hi Sakari, On Sat, Sep 8, 2012 at 12:16 AM, Sakari Ailus <sakari.ailus@xxxxxx> wrote: > Hi Prabhakar, > > > Prabhakar Lad wrote: >> >> Hi Sakari, >> >> Thanks for the review. >> >> On Wednesday 05 September 2012 12:42 AM, Sakari Ailus wrote: >>> >>> Hi Prabhakar, >>> >>> Thanks for the patch. I've got a few comments below. >>> >>> On Tue, Sep 04, 2012 at 11:07:52AM +0530, 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> >>>> Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> >>>> Reviewed-by: Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx> >>>> Cc: Sakari Ailus <sakari.ailus@xxxxxx> >>>> Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> >>>> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx> >>>> Cc: Hans de Goede <hdegoede@xxxxxxxxxx> >>>> Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> >>>> Cc: Rob Landley <rob@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 v4: >>>> 1: Aligned the description to fit appropriately in the >>>> para tag, pointed by Sylwester. >>>> >>>> Changes for v3: >>>> 1: Added better explanation for DPCM, pointed by Hans. >>>> >>>> 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 | 46 >>>> +++++++++++++++++++++++++- >>>> drivers/media/v4l2-core/v4l2-ctrls.c | 9 +++++ >>>> include/linux/videodev2.h | 5 +++ >>>> 3 files changed, 59 insertions(+), 1 deletions(-) >>>> >>>> diff --git a/Documentation/DocBook/media/v4l/controls.xml >>>> b/Documentation/DocBook/media/v4l/controls.xml >>>> index 93b9c68..ad873ea 100644 >>>> --- a/Documentation/DocBook/media/v4l/controls.xml >>>> +++ b/Documentation/DocBook/media/v4l/controls.xml >>>> @@ -4267,7 +4267,51 @@ 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"> Differential pulse-code modulation >>>> (DPCM) is a signal >>>> + encoder that uses the baseline of pulse-code modulation >>>> (PCM) but adds some >>>> + functionalities based on the prediction of the samples of >>>> the signal. The input >>>> + can be an analog signal or a digital signal. >>>> + >>>> + <para>If the input is a continuous-time analog signal, it >>>> needs to be sampled >>>> + first so that a discrete-time signal is the input to the >>>> DPCM encoder.</para> >>>> + >>>> + <para>Simple: take the values of two consecutive samples; if >>>> they are analog >>>> + samples, quantize them; calculate the difference between the >>>> first one and the >>>> + next; the output is the difference, and it can be further >>>> entropy coded.</para> >>>> + >>>> + <para>Advanced: instead of taking a difference relative to a >>>> previous input sample, >>>> + take the difference relative to the output of a local model >>>> of the decoder process; >>>> + in this option, the difference can be quantized, which >>>> allows a good way to >>>> + incorporate a controlled loss in the encoding.</para> >>> >>> >>> This is directly from Wikipedia, isn't it? >>> >> Yes. >> >>> What comes to the content, DPCM in the context of V4L2 media bus codes, >>> as a >>> digital interface, is always digital. So there's no need to document it. >>> Entropy coding is also out of the question: the samples of the currently >>> defined formats are equal in size. >>> >> Ok. > > > Could you replace the above with this text (with appropriate indentation > etc.) while keeping the reference to Wikipedia? > > ------8<------ > Differential pulse-code modulation (DPCM) compression can be used to > compress the samples into fewer bits than they would otherwise require. This > is done by calculating the difference between consecutive samples and > outputting the difference which in average is much smaller than the values > of the samples themselves since there is generally lots of correlation > between adjacent pixels. In decompression the original samples are > reconstructed. The process isn't lossless as the encoded sample size in bits > is less than the original. > > Formats using DPCM compression include <xref linkend="pixfmt-srggb10dpcm8" > />. > > This control is used to select the predictor used to encode the samples. > > The main difference between the simple and the advanced predictors is image > quality, with advanced predictor supposed to produce better quality images > as a result. Simple predictor can be used e.g. for testing purposes. > ------8<------ > Thanks for the definition. :) Thanks and Regards, --Prabhakar Lad > > Kind regards, > > -- > 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 -- 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
