Working with the Histogram

Purpose

This document describes the various APIs for working with a Histogram.

Introduction

A histogram provides details about the exposure and light on a scene. You can use the histogram to adjust the screen settings accordingly.

The code in this tutorial can be found in ecamextendedfunctest.cpp.

Working with a Histogram

The high level steps to work with histogram are shown here:

• Make sure that you call CCameraV2Histogram::PrepareClientHistogramL before calling CCameraV2Histogram::StartHistogram API.

• Use CCameraV2Histogram::StartHistogram call to start getting histogram notifications once a direct or a client based histogram is prepared.

• Use CCamera::CCameraV2Histogram::GetHistogramStateL to get the list of histograms that are currently active. A histogram continues to be in an active state if StartHistogram() has been called on it and has not been yet stopped.

• Use GetDirectHistogramPropertiesL API to get the current properties used by a direct histogram.

• Call UpdateDirectHistogramPropertiesL API to update the properties of a direct histogram with the new values and call GetDirectHistogramPropertiesL to verify it.

Receiving Histograms

The histogram data is received as follows:

• Use MDirectViewFinderObserver::ClientHistogramReady call back to notify the client about availability of the histogram data.

• If a call to CCameraV2Histogram::StartHistogram is made without a previous successful call to CCameraV2Histogram:: PrepareClientHistogramL, the callback returns KErrBadHandle.

• This provides a pointer to MHistogramV2Buffer that retrieves a single histogram.

• If the histogram requested is of direct type, it will be directly embedded into the direct viewfinder. If a non direct histogram is requested, the histogram data will be passed to the camera client.

Example

The following example illustrates the sequence for working with a histogram for client viewfinder.

1. Start a histogram.

   histogram_CVF->StartHistogram();

2. Confirm whether a specific histogram is active.

   TBool histogramActive = EFalse;
   histogram_CVF->GetHistogramStateL(histogramActive);

3. Get the current properties of a direct histogram.

   CCamera::CCameraV2Histogram::TDirectHistogramParameters histogramParameters;
   histogram_CVF->GetDirectHistogramPropertiesL(histogramParameters);

4. Update the properties of histogram with the new values.

   CCamera::CCameraV2Histogram::TDirectHistogramParameters histogramParameters;
   histogram_CVF->UpdateDirectHistogramPropertiesL(histogramParameters);