Re: [PATCH v4] media: v4l2-ctrls: add control for dpcm predictor
Hi Sakari, On Thu, Sep 13, 2012 at 6:29 AM, Laurent Pinchart laurent.pinch...@ideasonboard.com wrote: Hi Sakari, On Friday 07 September 2012 21:46:44 Sakari Ailus wrote: 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. If I remember correctly this control will be used on the receiver side on DaVinci, to decode pixels not encode them. How is the predictor used in that case ? Must it match the predictor used on the encoding side ? If so I expect documentation to be available somewhere. The OMAP3 ISP supports both DPCM encoding and decoding, and documents the predictors as - The simple predictor This predictor uses only the previous same color component value as a prediction value. Therefore, only two-pixel memory is required. - The advanced predictor This predictor uses four previous pixel values, when the prediction value is evaluated. This means that also the other color component values are used, when the prediction value has been defined. It also states the the simple predictor is preferred for 10-8-10 conversion, and the advanced predictor for 10-7-10 and 10-6-10 conversion. What do you suggest ? Regards, --Prabhakar Lad 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-- -- Regards, Laurent Pinchart ___ Davinci-linux-open-source mailing list davinci-linux-open-sou...@linux.davincidsp.com http://linux.davincidsp.com/mailman/listinfo/davinci-linux-open-source -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v4] media: v4l2-ctrls: add control for dpcm predictor
Hi Sakari, On Friday 07 September 2012 21:46:44 Sakari Ailus wrote: 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. If I remember correctly this control will be used on the receiver side on DaVinci, to decode pixels not encode them. How is the predictor used in that case ? Must it match the predictor used on the encoding side ? If so I expect documentation to be available somewhere. The OMAP3 ISP supports both DPCM encoding and decoding, and documents the predictors as - The simple predictor This predictor uses only the previous same color component value as a prediction value. Therefore, only two-pixel memory is required. - The advanced predictor This predictor uses four previous pixel values, when the prediction value is evaluated. This means that also the other color component values are used, when the prediction value has been defined. It also states the the simple predictor is preferred for 10-8-10 conversion, and the advanced predictor for 10-7-10 and 10-6-10 conversion. 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-- -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v4] media: v4l2-ctrls: add control for dpcm predictor
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@ti.com 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@ti.com Signed-off-by: Manjunath Hadli manjunath.ha...@ti.com Acked-by: Hans Verkuil hans.verk...@cisco.com Reviewed-by: Sylwester Nawrocki s.nawro...@samsung.com Cc: Sakari Ailus sakari.ai...@iki.fi Cc: Laurent Pinchart laurent.pinch...@ideasonboard.com Cc: Mauro Carvalho Chehab mche...@infradead.org Cc: Hans de Goede hdego...@redhat.com Cc: Kyungmin Park kyungmin.p...@samsung.com Cc: Rob Landley r...@landley.net --- 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 - rowentry/entry/row + row + entry spanname=idconstantV4L2_CID_DPCM_PREDICTOR/constant/entry + entrymenu/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. + + paraIf 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 + + paraSimple: 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 + + paraAdvanced: 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-- Kind regards, -- Sakari Ailus sakari.ai...@iki.fi -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v4] media: v4l2-ctrls: add control for dpcm predictor
Hi Sakari, On Sat, Sep 8, 2012 at 12:16 AM, Sakari Ailus sakari.ai...@iki.fi 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@ti.com 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@ti.com Signed-off-by: Manjunath Hadli manjunath.ha...@ti.com Acked-by: Hans Verkuil hans.verk...@cisco.com Reviewed-by: Sylwester Nawrocki s.nawro...@samsung.com Cc: Sakari Ailus sakari.ai...@iki.fi Cc: Laurent Pinchart laurent.pinch...@ideasonboard.com Cc: Mauro Carvalho Chehab mche...@infradead.org Cc: Hans de Goede hdego...@redhat.com Cc: Kyungmin Park kyungmin.p...@samsung.com Cc: Rob Landley r...@landley.net --- 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 - rowentry/entry/row + row + entry spanname=idconstantV4L2_CID_DPCM_PREDICTOR/constant/entry + entrymenu/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. + + paraIf 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 + + paraSimple: 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 + + paraAdvanced: 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
Re: [PATCH v4] media: v4l2-ctrls: add control for dpcm predictor
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@ti.com 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@ti.com Signed-off-by: Manjunath Hadli manjunath.ha...@ti.com Acked-by: Hans Verkuil hans.verk...@cisco.com Reviewed-by: Sylwester Nawrocki s.nawro...@samsung.com Cc: Sakari Ailus sakari.ai...@iki.fi Cc: Laurent Pinchart laurent.pinch...@ideasonboard.com Cc: Mauro Carvalho Chehab mche...@infradead.org Cc: Hans de Goede hdego...@redhat.com Cc: Kyungmin Park kyungmin.p...@samsung.com Cc: Rob Landley r...@landley.net --- 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 - rowentry/entry/row + row + entry spanname=idconstantV4L2_CID_DPCM_PREDICTOR/constant/entry + entrymenu/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. + + paraIf 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 + + paraSimple: 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 + + paraAdvanced: 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? 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. Another thing what I'm not sure is the definition of the simple and advanced encoders. I've seen sensors that allow you to choose which one to use, but the documentation hasn't stated what the actual implementation is. Does TI documentation do so? In V4L2 documentation we should state what is common in the hardware documentation, and that is mostly limited to simple and advanced. I really don't know enough that I could say what the exact implamentation of those two are in all of the cases. I suggest we leave just a few words of the DPCM compression itself (roughly the factual content of the first paragraph with the exception of the reference to analogue signal) and a link to Wikipedia. + paraApplying one of these two processes, short-term redundancy (positive correlation of + nearby values) of the signal is eliminated; compression ratios on the order of 2 to 4 + can be achieved if differences are subsequently entropy coded, because the entropy of + the difference signal is much smaller than that of the original discrete signal treated + as independent samples.For more information about DPCM see ulink + url=http://en.wikipedia.org/wiki/Differential_pulse-code_modulation;Wikipedia/ulink./para + /entry + /row + row + entrytbl spanname=descr cols=2 + tbody valign=top + row +
Re: [PATCH v4] media: v4l2-ctrls: add control for dpcm predictor
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@ti.com 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@ti.com Signed-off-by: Manjunath Hadli manjunath.ha...@ti.com Acked-by: Hans Verkuil hans.verk...@cisco.com Reviewed-by: Sylwester Nawrocki s.nawro...@samsung.com Cc: Sakari Ailus sakari.ai...@iki.fi Cc: Laurent Pinchart laurent.pinch...@ideasonboard.com Cc: Mauro Carvalho Chehab mche...@infradead.org Cc: Hans de Goede hdego...@redhat.com Cc: Kyungmin Park kyungmin.p...@samsung.com Cc: Rob Landley r...@landley.net --- 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 - rowentry/entry/row + row +entry spanname=idconstantV4L2_CID_DPCM_PREDICTOR/constant/entry +entrymenu/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. + +paraIf 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 + +paraSimple: 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 + +paraAdvanced: 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. Another thing what I'm not sure is the definition of the simple and advanced encoders. I've seen sensors that allow you to choose which one to use, but the documentation hasn't stated what the actual implementation is. Does TI documentation do so? Couldn't find much apart from this 'The DPCM compression system uses two different predictors; one is simple and the other is complex. Predictor1 is very simple, so the processing power and the memory requirements are reduced with it (when the image quality is already high enough). Predictor2 gives a slightly better prediction for pixel value and the image quality can be improved with it.' In V4L2 documentation we should state what is common in the hardware documentation, and that is mostly limited to simple and advanced. I really don't know enough that I could say what the exact implamentation of those two are in all of the cases. I suggest we leave just a few words of the DPCM compression itself (roughly the factual content of the first paragraph with the exception of the reference to analogue signal) and a link to Wikipedia. Ok. +paraApplying one of these two processes, short-term redundancy (positive correlation of +nearby values) of the signal is eliminated; compression ratios on the order of 2 to 4 +can be achieved if differences are subsequently
[PATCH v4] media: v4l2-ctrls: add control for dpcm predictor
From: Lad, Prabhakar prabhakar@ti.com
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@ti.com
Signed-off-by: Manjunath Hadli manjunath.ha...@ti.com
Acked-by: Hans Verkuil hans.verk...@cisco.com
Reviewed-by: Sylwester Nawrocki s.nawro...@samsung.com
Cc: Sakari Ailus sakari.ai...@iki.fi
Cc: Laurent Pinchart laurent.pinch...@ideasonboard.com
Cc: Mauro Carvalho Chehab mche...@infradead.org
Cc: Hans de Goede hdego...@redhat.com
Cc: Kyungmin Park kyungmin.p...@samsung.com
Cc: Rob Landley r...@landley.net
---
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
- rowentry/entry/row
+ row
+ entry
spanname=idconstantV4L2_CID_DPCM_PREDICTOR/constant/entry
+ entrymenu/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.
+
+ paraIf 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
+
+ paraSimple: 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
+
+ paraAdvanced: 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
+
+ paraApplying one of these two processes, short-term redundancy
(positive correlation of
+ nearby values) of the signal is eliminated; compression ratios on
the order of 2 to 4
+ can be achieved if differences are subsequently entropy coded,
because the entropy of
+ the difference signal is much smaller than that of the original
discrete signal treated
+ as independent samples.For more information about DPCM see ulink
+
url=http://en.wikipedia.org/wiki/Differential_pulse-code_modulation;Wikipedia/ulink./para
+ /entry
+ /row
+ row
+ entrytbl spanname=descr cols=2
+ tbody valign=top
+ row
+entryconstantV4L2_DPCM_PREDICTOR_SIMPLE/constant/entry
+ entryPredictor type is simple/entry
+ /row
+ row
+
entryconstantV4L2_DPCM_PREDICTOR_ADVANCED/constant/entry
+ entryPredictor type is advanced/entry
+ /row
+ /tbody
+ /entrytbl
+ /row
+ rowentry/entry/row
/tbody
/tgroup
/table
diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c
b/drivers/media/v4l2-core/v4l2-ctrls.c
index b6a2ee7..2d7bc15 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -425,6 +425,11 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
Gray,
NULL,
};
+ static const char * const dpcm_predictor[] = {
+ Simple Predictor,
+ Advanced Predictor,
+ NULL,
+ };
switch (id) {
case V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ:
@@ -502,6 +507,8 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
return mpeg4_profile;
case V4L2_CID_JPEG_CHROMA_SUBSAMPLING:
return jpeg_chroma_subsampling;
+
