Re: [PATCH 00/18] media: microchip-isc: Color correction and histogram stats

Balamanikandan.Gunasundar
2025-10-15T06:05:14Z

Hi  Kieran,

On 10/10/25 1:51 pm, Kieran Bingham wrote:
>> Hi Bala,
>>
>> On 10/9/25 18:52, Balamanikandan Gunasundar wrote:
>>> Hi,
>>>
>>> This patch series has a set of enhancements to the Microchip Image Sensor
>>> Controller driver. The objective is to expand its image processing
>>> capabilities and to improve the colors.
>>>
>>> This series also introduces a new stats driver that exposes the histogram
>>> data to userspace via v4l2 controls. This allows applications such as
>>> libcamera to access real time image statistics for advanced image
>>> processing like automatic exposure, white balance adjustments etc.
> How much data do you anticipate to be passing through controls? (What
> can the hardware provide in total if we look at the bigger picture to
> support the full device?)
Thanks for the feedback. Currently the hardware provides histogram data
with 256 bins per color (R, G, B and Y) each 32 bit wide. So roughly
around 4 x 256 x 4 = 4K of data per frame. The intent to use  it as v4l2
controls was to make this data easily accessible to user space without a
need for a new data interface initially. However I agree that we may
expand the statistics for future ISP blocks to include region based
stats (We are already in discussion with the design)
>
> For all other ISPs we've been working towards using structured parameter
> buffers to pass data - and we've been making that format extensible,
> which I think could also be a design that can apply to statistics.

That sounds great and we can certainly explore aligning with the
structured buffers for histogram data and any other future statistics.

Thanks,

Bala

>
> This would greatly reduce the overhead of managing 'one control per
> value' ... or things like passing large tables (like a lens shading
> table perhaps) through controls.
>
> --
> Kieran