Added the possibility to define a filter in the NativePreview mechanism, e.g. for hex decoding

src/epsimage.cpp

@@ -697,6 +697,7 @@ namespace {
                 nativePreview.size_ = sizeWmf;
                 nativePreview.width_ = 0;
                 nativePreview.height_ = 0;
+                nativePreview.filter_ = "";
                 nativePreview.mimeType_ = "image/x-wmf";
                 nativePreviews.push_back(nativePreview);
             }
@@ -706,6 +707,7 @@ namespace {
                 nativePreview.size_ = sizeTiff;
                 nativePreview.width_ = 0;
                 nativePreview.height_ = 0;
+                nativePreview.filter_ = "";
                 nativePreview.mimeType_ = "image/tiff";
                 nativePreviews.push_back(nativePreview);
             }

src/image.hpp

@@ -64,6 +64,7 @@ namespace Exiv2 {
         uint32_t size_;
         uint32_t width_;
         uint32_t height_;
+        std::string filter_;
         std::string mimeType_;
     };
 

src/preview.cpp

@@ -403,10 +403,14 @@ namespace {
     {
         if (!(0 <= parIdx && static_cast<size_t>(parIdx) < image.nativePreviews().size())) return;
         nativePreview_ = image.nativePreviews()[parIdx];
-        size_ = nativePreview_.size_;
         width_ = nativePreview_.width_;
         height_ = nativePreview_.height_;
         valid_ = true;
+        if (nativePreview_.size_ == 0) {
+            size_ = getData().size_;
+        } else {
+            size_ = nativePreview_.size_;
+        }
     }
 
     Loader::AutoPtr createLoaderNative(PreviewId id, const Image &image, int parIdx)
@@ -452,7 +456,11 @@ namespace {
 #endif
             return DataBuf();
         }
-        return DataBuf(data + nativePreview_.position_, nativePreview_.size_);
+        if (nativePreview_.filter_ == "") {
+            return DataBuf(data + nativePreview_.position_, nativePreview_.size_);
+        } else {
+            throw Error(1, "Invalid native preview filter: " + nativePreview_.filter_);
+        }
     }
 
     bool LoaderNative::readDimensions()

src/psdimage.cpp

@@ -334,6 +334,7 @@ namespace Exiv2 {
                     if (io_->error() || io_->eof()) throw Error(14);
 
                     if (format == 1) {
+                        nativePreview.filter_ = "";
                         nativePreview.mimeType_ = "image/jpeg";
                         nativePreviews_.push_back(nativePreview);
                     } else {