diff --git a/reader.lua b/reader.lua
index 68e979596..9f24c53e7 100755
--- a/reader.lua
+++ b/reader.lua
@@ -195,6 +195,7 @@ function show(no)
 		rcount = rcount + 1
 		fb:refresh(1)
 	end
+	slot_visible = slot;
 end
 
 function goto(no)
@@ -209,6 +210,21 @@ function goto(no)
 	end
 end
 
+function modify_gamma(offset)
+	local slot = slot_visible
+	local gamma = cache[slot].dc:getGamma();
+	if gamma == -1 then
+		gamma = 1
+	end
+	print("modify_gamma slot="..slot.." gamma="..gamma.." offset="..offset)
+	gamma = gamma + offset;
+	cache[slot].dc:setGamma( gamma );
+	optarg["G"] = gamma; -- for next page
+	cache[slot].page:draw(cache[slot].dc, cache[slot].bb, 0, 0)
+	fb:blitFullFrom(cache[slot].bb)
+	fb:refresh(0)
+end
+
 function mainloop()
 	while 1 do
 		local ev = input.waitForEvent()
@@ -224,6 +240,10 @@ function mainloop()
 				print(cache)
 			elseif ev.code == KEY_BACK then
 				return
+			elseif ev.code == KEY_UP then
+				modify_gamma( 0.2 )
+			elseif ev.code == KEY_DOWN then
+				modify_gamma( -0.2 )
 			end
 			local nsecs, nusecs = util.gettime()
 			local dur = (nsecs - secs) * 1000000 + nusecs - usecs