[PATCH v3] ipa: libipa: histogram: Add transform parameter to constructor

[Paul Elder]

On Wed, May 08, 2024 at 07:35:46PM +0900, Paul Elder wrote:
> Add a parameter to the histogram constructor that takes a transformation
> function to apply to all the bins upon construction.
> 
> This is necessary notably for the rkisp1, as the values reported from
> the hardware are 20 bits where the upper 16-bits are meaningful integer
> values and the lower 4 bits are fractional and meant to be discarded. As
> adding a right-shift parameter is probably too specialized, a generic
> function is added as a parameter instead.
> 
> Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>

Oops, I forgot to pull in Kieran's and Dan's rb tags.


Paul

> 
> ---
> Changes in v3:
> - make the transform function a template parameter, and optimize the
>   constructor
> 
> This used to be "ipa: libipa: histogram: Add rshift parameter to
> constructor"
> 
> Changes in v2:
> - change rshift parameter to a function parameter
> ---
>  src/ipa/libipa/histogram.cpp |  8 +-------
>  src/ipa/libipa/histogram.h   | 14 ++++++++++++--
>  2 files changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/src/ipa/libipa/histogram.cpp b/src/ipa/libipa/histogram.cpp
> index c1aac59b..628e3755 100644
> --- a/src/ipa/libipa/histogram.cpp
> +++ b/src/ipa/libipa/histogram.cpp
> @@ -40,14 +40,8 @@ namespace ipa {
>  /**
>   * \brief Create a cumulative histogram
>   * \param[in] data A pre-sorted histogram to be passed
> + * \param[in] transform The transformation function to apply to every bin
>   */
> -Histogram::Histogram(Span<const uint32_t> data)
> -{
> -	cumulative_.reserve(data.size());
> -	cumulative_.push_back(0);
> -	for (const uint32_t &value : data)
> -		cumulative_.push_back(cumulative_.back() + value);
> -}
>  
>  /**
>   * \fn Histogram::bins()
> diff --git a/src/ipa/libipa/histogram.h b/src/ipa/libipa/histogram.h
> index 54bb2a19..26326125 100644
> --- a/src/ipa/libipa/histogram.h
> +++ b/src/ipa/libipa/histogram.h
> @@ -10,10 +10,10 @@
>  #include <assert.h>
>  #include <limits.h>
>  #include <stdint.h>
> -
>  #include <vector>
>  
>  #include <libcamera/base/span.h>
> +#include <libcamera/base/utils.h>
>  
>  namespace libcamera {
>  
> @@ -23,7 +23,17 @@ class Histogram
>  {
>  public:
>  	Histogram() { cumulative_.push_back(0); }
> -	Histogram(Span<const uint32_t> data);
> +
> +	template<typename Transform>
> +	Histogram(Span<const uint32_t> data,
> +		  Transform transform = [](uint32_t x) { return x; })
> +	{
> +		cumulative_.resize(data.size() + 1);
> +		cumulative_[0] = 0;
> +		for (const auto &[i, value] : utils::enumerate(data))
> +			cumulative_[i + 1] = cumulative_[i] + transform(value);
> +	}
> +
>  	size_t bins() const { return cumulative_.size() - 1; }
>  	uint64_t total() const { return cumulative_[cumulative_.size() - 1]; }
>  	uint64_t cumulativeFrequency(double bin) const;
> -- 
> 2.39.2
>