diff --git a/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/image/PDImageXObject.java b/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/image/PDImageXObject.java
index e85b098b047..9559616a290 100644
--- a/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/image/PDImageXObject.java
+++ b/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/image/PDImageXObject.java
@@ -84,6 +84,9 @@ public final class PDImageXObject extends PDXObject implements PDImage
     private boolean jpxValuesInitialized = false;
     private BufferedImage jpxSMask = null;
 
+    // PDFBOX-5876: upper bound for the subsampling used by initJPXValues method.
+    private static final int JPX_METADATA_SUBSAMPLING = 8;
+
     /**
      * current resource dictionary (has color spaces)
      */
@@ -739,7 +742,12 @@ private void initJPXValues()
         // bits per component
         // the colorspace of the image is used if the dictionary doesn't provide any value
         PDStream stream = getStream();
-        try (COSInputStream is = stream.createInputStream())
+        // PDFBOX-5876: subsample this metadata-only read, see the JPX_METADATA_SUBSAMPLING field.
+        // Not when a soft mask may be extracted from the image data, because that mask is kept
+        // and used later at its own resolution, so it must not be subsampled.
+        try (COSInputStream is = mayHaveJPXSMask()
+                ? stream.createInputStream()
+                : stream.createInputStream(new DecodeOptions(JPX_METADATA_SUBSAMPLING)))
         {
             DecodeResult decodeResult = is.getDecodeResult();
             stream.getCOSObject().addAll(decodeResult.getParameters());
@@ -756,6 +764,19 @@ private void initJPXValues()
         }
     }
 
+    /**
+     * Tells whether decoding this image may produce a soft mask taken from the image data
+     * (PDFBOX-5657). {@code JPXFilter} only extracts such a mask when the image dictionary has no
+     * /ColorSpace entry and a positive /SMaskInData entry, so both are checked here to mirror it.
+     *
+     * @return true if a soft mask may be extracted from the image data.
+     */
+    private boolean mayHaveJPXSMask()
+    {
+        COSDictionary dict = getCOSObject();
+        return !dict.containsKey(COSName.COLORSPACE) && dict.getInt(COSName.SMASK_IN_DATA) > 0;
+    }
+
     /**
      * High-quality image scaling.
      */