FEATURE: histogram equalization for images

Pradeep · Pradeep · commit ffc47869d851 · 2015-02-23T13:45:10.000-05:00
diff --git a/include/af/image.h b/include/af/image.h
@@ -72,6 +72,8 @@ AFAPI array rgb2gray(const array& in, const float rPercent=0.2126f, const float
 
 AFAPI array gray2rgb(const array& in, const float rFactor=1.0, const float gFactor=1.0, const float bFactor=1.0);
 
+AFAPI array histequal(const array& in, const array& hist);
+
 }
 #endif
 
@@ -151,6 +153,8 @@ extern "C" {
 
     AFAPI af_err af_gray2rgb(af_array* out, const af_array in, const float rFactor, const float gFactor, const float bFactor);
 
+    AFAPI af_err af_histequal(af_array *out, const af_array in, const af_array hist);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/api/c/histeq.cpp b/src/api/c/histeq.cpp
@@ -0,0 +1,93 @@
+/*******************************************************
+ * Copyright (c) 2014, ArrayFire
+ * All rights reserved.
+ *
+ * This file is distributed under 3-clause BSD license.
+ * The complete license agreement can be obtained at:
+ * http://arrayfire.com/licenses/BSD-3-Clause
+ ********************************************************/
+
+#include <af/image.h>
+#include <af/index.h>
+#include <af/defines.h>
+#include <err_common.hpp>
+#include <handle.hpp>
+#include <backend.hpp>
+#include <cast.hpp>
+#include <scan.hpp>
+#include <arith.hpp>
+#include <reduce.hpp>
+#include <ArrayIndex.hpp>
+
+using namespace detail;
+
+template<typename T, typename hType>
+static af_array histequal(const af_array& in, const af_array& hist)
+{
+    const Array<T> input = getArray<T>(in);
+
+    af_array vInput = 0;
+    AF_CHECK(af_flat(&vInput, in));
+
+    Array<float>* fHist  = cast<float>(getArray<hType>(hist));
+
+    dim4 hDims = fHist->dims();
+    dim_type grayLevels = fHist->elements();
+
+    Array<float>* cdf = detail::scan<af_add_t, float, float>(*fHist, 0);
+
+    float minCdf = detail::reduce_all<af_min_t, float, float>(*cdf);
+    float maxCdf = detail::reduce_all<af_max_t, float, float>(*cdf);
+    float factor = (float)(grayLevels-1)/(maxCdf - minCdf);
+
+    // constant array of min value from cdf
+    Array<float>* minCnst = createValueArray<float>(hDims, minCdf);
+    // constant array of factor variable
+    Array<float>* facCnst = createValueArray<float>(hDims, factor);
+    // cdf(i) - min for all elements
+    Array<float>* diff    = detail::arithOp<float, af_sub_t>(*cdf, *minCnst, hDims);
+    // multiply factor with difference
+    Array<float>* normCdf = detail::arithOp<float, af_mul_t>(*diff, *facCnst, hDims);
+    // index input array with normalized cdf array
+    Array<float>* idxArr  = detail::arrayIndex<float, T>(*normCdf, getArray<T>(vInput), 0);
+
+    Array<T>* result = cast<T>(*idxArr);
+
+    destroyArray<float>(*idxArr);
+    destroyArray<float>(*normCdf);
+    destroyArray<float>(*diff);
+    destroyArray<float>(*facCnst);
+    destroyArray<float>(*minCnst);
+    destroyArray<float>(*cdf);
+    destroyArray<float>(*fHist);
+    AF_CHECK(af_destroy_array(vInput));
+
+    return getHandle<T>(*result);
+}
+
+af_err af_histequal(af_array *out, const af_array in, const af_array hist)
+{
+    try {
+        ArrayInfo dataInfo = getInfo(in);
+        ArrayInfo histInfo = getInfo(hist);
+
+        af_dtype dataType  = dataInfo.getType();
+        af::dim4 histDims  = histInfo.dims();
+
+        ARG_ASSERT(2, (histDims.ndims()==1));
+
+        af_array output = 0;
+        switch(dataType) {
+            case f64: output = histequal<double, uint>(in, hist); break;
+            case f32: output = histequal<float , uint>(in, hist); break;
+            case s32: output = histequal<int   , uint>(in, hist); break;
+            case u32: output = histequal<uint  , uint>(in, hist); break;
+            case u8 : output = histequal<uchar , uint>(in, hist); break;
+            default : TYPE_ERROR(1, dataType);
+        }
+        std::swap(*out,output);
+    }
+    CATCHALL;
+
+    return AF_SUCCESS;
+}
diff --git a/src/api/cpp/histogram.cpp b/src/api/cpp/histogram.cpp
@@ -28,4 +28,11 @@ array histogram(const array &in, const unsigned nbins)
     return array(out);
 }
 
+array histequal(const array& in, const array& hist)
+{
+    af_array temp = 0;
+    AF_THROW(af_histequal(&temp, in.get(), hist.get()));
+    return array(temp);
+}
+
 }

Original file line number	Diff line number	Diff line change
`@@ -72,6 +72,8 @@ AFAPI array rgb2gray(const array& in, const float rPercent=0.2126f, const float`
`72`	`72`
`73`	`73`	`AFAPI array gray2rgb(const array& in, const float rFactor=1.0, const float gFactor=1.0, const float bFactor=1.0);`
`74`	`74`
	`75`	`+AFAPI array histequal(const array& in, const array& hist);`
	`76`	`+`
`75`	`77`	`}`
`76`	`78`	`#endif`
`77`	`79`
`@@ -151,6 +153,8 @@ extern "C" {`
`151`	`153`
`152`	`154`	`AFAPI af_err af_gray2rgb(af_array* out, const af_array in, const float rFactor, const float gFactor, const float bFactor);`
`153`	`155`
	`156`	`+ AFAPI af_err af_histequal(af_array *out, const af_array in, const af_array hist);`
	`157`	`+`
`154`	`158`	`#ifdef __cplusplus`
`155`	`159`	`}`
`156`	`160`	`#endif`
Original file line number	Diff line number	Diff line change
`@@ -28,4 +28,11 @@ array histogram(const array &in, const unsigned nbins)`
`28`	`28`	`return array(out);`
`29`	`29`	`}`
`30`	`30`
	`31`	`+array histequal(const array& in, const array& hist)`
	`32`	`+{`
	`33`	`+ af_array temp = 0;`
	`34`	`+ AF_THROW(af_histequal(&temp, in.get(), hist.get()));`
	`35`	`+ return array(temp);`
	`36`	`+}`
	`37`	`+`
`31`	`38`	`}`