diff --git a/sane/scanned_img.cpp b/sane/scanned_img.cpp
index 69e093b..fa4c22a 100644
--- a/sane/scanned_img.cpp
+++ b/sane/scanned_img.cpp
@@ -469,6 +469,7 @@ std::string scanned_img::file_header(SANE_ImageType type, float resolution)
 			pal_size = 2 * sizeof(int);
 		else if (bih.biBitCount == 8)
 			pal_size = 256 * sizeof(int);
+		bih.biClrUsed = pal_size / sizeof(int);			// some APP (PJScanner.exe ¹â´ó¡­¡­) use this field to calculate pallete
 
 		{
 			BITMAPFILEHEADER	fh = { 0 };