StAVImage::save() - expose Compression level parameter in API and app…

…ly to PNG and JPEG
gkv311 · Jan 17, 2025 · 3f9c0b2 · 3f9c0b2
1 parent 614c904
commit 3f9c0b2
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Showing 4 changed files with 28 additions and 4 deletions.
diff --git a/StShared/StAVImage.cpp b/StShared/StAVImage.cpp
@@ -701,7 +701,13 @@ bool StAVImage::save(const StString& theFilePath,
             myCodecCtx->height  = (int )anImage.getSizeY();
             myCodecCtx->time_base.num = 1;
             myCodecCtx->time_base.den = 1;
-            myCodecCtx->compression_level = 9; // 0..9
+
+            // PNG compression level is within [0..9] range
+            static const int PNG_QLOWER = 0;
+            static const int PNG_QUPPER = 9;
+            const float aRatio = stClamp(theParams.Compression >= 0.0f ? theParams.Compression : 1.0f, 0.0f, 1.0f);
+            int aQLevel = stRound(stLerp(float(PNG_QLOWER), float(PNG_QUPPER), aRatio));
+            myCodecCtx->compression_level = aQLevel;
             break;
         }
         case ST_TYPE_JPEG:
@@ -746,7 +752,13 @@ bool StAVImage::save(const StString& theFilePath,
             myCodecCtx->height  = (int )anImage.getSizeY();
             myCodecCtx->time_base.num = 1;
             myCodecCtx->time_base.den = 1;
-            myCodecCtx->qmin = myCodecCtx->qmax = 5; // quality factor - lesser is better
+
+            // quantizer factor within 1..31 range, lesser is better
+            static const int JPEG_QLOWER = 1;
+            static const int JPEG_QUPPER = 31;
+            const float aRatio = stClamp(theParams.Compression >= 0.0f ? theParams.Compression : 0.10f, 0.0f, 1.0f);
+            int aQFactor = stRound(stLerp(float(JPEG_QLOWER), float(JPEG_QUPPER), aRatio));
+            myCodecCtx->qmin = myCodecCtx->qmax = aQFactor;
             break;
         }
         case ST_TYPE_NONE:

diff --git a/include/StImage/StImageFile.h b/include/StImage/StImageFile.h
@@ -58,8 +58,10 @@ class StImageFile : public StImage {
         ImageType  SaveImageType;
         /** Stereo format to be stored as metadata. */
         StFormat   StereoFormat;
+        /** Compression level within [0..1] range (0 minimal compression, 1 maximum, -1 default). */
+        float      Compression;
 
-        SaveImageParams() : SaveImageType(ST_TYPE_NONE), StereoFormat(StFormat_AUTO) {}
+        SaveImageParams() : SaveImageType(ST_TYPE_NONE), StereoFormat(StFormat_AUTO), Compression(-1.0) {}
     };
 
         public:

diff --git a/include/StTemplates/StTemplates.h b/include/StTemplates/StTemplates.h
@@ -76,4 +76,14 @@ inline Type stClamp(const Type theValue,
     return theValue;
 }
 
+/**
+ * Compute linear interpolation between two values.
+ * @param theT interpolation coefficient 0..1
+ * @return interpolation result
+ */
+template<typename Type, typename ElemType>
+inline Type stLerp(const Type& theFrom, const Type& theTo, const ElemType theT) {
+    return theFrom * (ElemType(1) - theT) + theTo * theT;
+}
+
 #endif //__StTemplates_H__
diff --git a/include/StTemplates/StVec3.h b/include/StTemplates/StVec3.h
@@ -345,7 +345,7 @@ class StVec3 {
     }
 
     /**
-     * Compute linear interpolation between to vectors.
+     * Compute linear interpolation between two vectors.
      * @param theT (const Element_t ) - interpolation coefficient 0..1;
      * @return interpolation result.
      */