diff --git a/src/output.zig b/src/output.zig
index 95d4603..3bd687b 100644
--- a/src/output.zig
+++ b/src/output.zig
@@ -16,17 +16,17 @@ const HuffCode = struct {
 
 const Scan = struct {
     arena: std.heap.ArenaAllocator,
-    diffs: [3]i16,
+    dc_diffs: [3]i16,
     rles: [3]RLE_Seq,
     freqs: [4][]u32,
     huffs: [4]Huffman,
 
     const Self = @This();
 
-    fn init(alloc_: std.mem.Allocator) !Self {
-        var arena = std.heap.ArenaAllocator.init(alloc_);
+    fn init(alloc_root: std.mem.Allocator) !Self {
+        var arena = std.heap.ArenaAllocator.init(alloc_root);
         var alloc = arena.allocator();
-        return Self{ .arena = arena, .diffs = [3]i16{ 0, 0, 0 }, .rles = [3]RLE_Seq{
+        return Self{ .arena = arena, .dc_diffs = [3]i16{ 0, 0, 0 }, .rles = [3]RLE_Seq{
             RLE_Seq.init(alloc),
             RLE_Seq.init(alloc),
             RLE_Seq.init(alloc),
@@ -40,14 +40,36 @@ const Scan = struct {
     fn deinit(self: *Self) void {
         self.arena.deinit();
     }
+
+    fn do_rle_freq_pass(self: *Self, buff: *const util.Buffers) !void {
+        const h = buff.Y_quant.len;
+        const w = buff.Y_quant[0].len;
+
+        for (0..h) |x| {
+            for (0..w) |y| {
+                for (0..4) |Y_sub_i| {
+                    try parse_block(&buff.Y_quant[x][y][Y_sub_i], &self.dc_diffs[0], &self.rles[0], self.freqs[0], self.freqs[1]);
+                }
+                try parse_block(&buff.U_quant[x][y], &self.dc_diffs[1], &self.rles[1], self.freqs[2], self.freqs[3]);
+                try parse_block(&buff.V_quant[x][y], &self.dc_diffs[2], &self.rles[2], self.freqs[2], self.freqs[3]);
+            }
+        }
+    }
 };
 
+fn parse_block(block: *util.BlockQuantized, dc_diff: *i16, dc_rle: *RLE_Seq, dc_freqs: []u32, ac_freqs: []u32) !void {
+    _ = ac_freqs;
+    _ = dc_freqs;
+    _ = dc_rle;
+    _ = dc_diff;
+    _ = block;
+}
+
 pub fn generate_jpg(buff: util.Buffers, alloc: std.mem.Allocator) !void {
-    _ = buff;
     var scan_data = try Scan.init(alloc);
     defer scan_data.deinit();
 
-    scan_data.do_rle_freq_pass(buff);
+    try scan_data.do_rle_freq_pass(&buff);
 
     // rle, huffman pass
     // file headers