diff --git a/nimPNG/filters.nim b/nimPNG/filters.nim
index 81107ed..ade7c2f 100644
--- a/nimPNG/filters.nim
+++ b/nimPNG/filters.nim
@@ -8,6 +8,17 @@ type
     FLT_AVERAGE,
     FLT_PAETH
 
+  PNGPass* = object
+    w*, h*: array[0..6, int]
+    filterStart*, paddedStart*, start*: array[0..7, int]
+
+const
+  # shared values used by multiple Adam7 related functions
+  ADAM7_IX = [ 0, 4, 0, 2, 0, 1, 0 ] # x start values
+  ADAM7_IY = [ 0, 0, 4, 0, 2, 0, 1 ] # y start values
+  ADAM7_DX = [ 8, 8, 4, 4, 2, 2, 1 ] # x delta values
+  ADAM7_DY = [ 8, 8, 8, 4, 4, 2, 2 ] # y delta values
+
 # Paeth predicter, used by PNG filter type 4
 proc paethPredictor(a, b, c: int): uint =
   let pa = abs(b - c)
@@ -102,7 +113,6 @@ proc filterZero*(output: var openArray[byte], input: openArray[byte], w, h, bpp:
       byteWidth, lineBytes, FLT_NONE)
     prevIndex = inIndex
 
-
 proc filterMinsum*(output: var openArray[byte], input: openArray[byte], w, h, bpp: int) =
   let lineBytes = (w * bpp + 7) div 8
   let byteWidth = (bpp + 7) div 8
@@ -389,3 +399,158 @@ proc unfilter*(output: var openArray[byte], input: openArray[byte], w, h, bpp: i
       output.toOpenArray(prevIndex, output.len-1), # prevLine
       byteWidth, lineBytes, filterType)
     prevIndex = outIndex
+
+proc readBitFromReversedStream(bitptr: var int, bitstream: openArray[byte]): int =
+  result = ((int(bitstream[bitptr shr 3]) shr (7 - (bitptr and 0x7))) and 1)
+  inc bitptr
+
+proc readBitsFromReversedStream(bitptr: var int, bitstream: openArray[byte], nbits: int): int =
+  result = 0
+  var i = nbits - 1
+  while i > -1:
+    result += readBitFromReversedStream(bitptr, bitstream) shl i
+    dec i
+
+proc `&=`(a: var byte, b: byte) =
+  a = byte(int(a) and int(b))
+
+proc `|=`(a: var byte, b: byte) =
+  a = byte(int(a) or int(b))
+
+proc setBitOfReversedStream0(bitptr: var int, bitstream: var openArray[byte], bit: int) =
+  # the current bit in bitstream must be 0 for this to work
+  if bit != 0:
+    # earlier bit of huffman code is in a lesser significant bit of an earlier byte
+    bitstream[bitptr shr 3] |= byte(bit shl (7 - (bitptr and 0x7)))
+  inc bitptr
+
+proc setBitOfReversedStream(bitptr: var int, bitstream: var openArray[byte], bit: int) =
+  # the current bit in bitstream may be 0 or 1 for this to work
+  if bit == 0: bitstream[bitptr shr 3] &= byte(not (1 shl (7 - (bitptr and 0x7))))
+  else: bitstream[bitptr shr 3] |= byte(1 shl (7 - (bitptr and 0x7)))
+  inc bitptr
+
+proc removePaddingBits(output: var openArray[byte], input: openArray[byte], olinebits, ilinebits, h: int) =
+  # After filtering there are still padding bits if scanLines have non multiple of 8 bit amounts. They need
+  # to be removed (except at last scanLine of (Adam7-reduced) image) before working with pure image buffers
+  # for the Adam7 code, the color convert code and the output to the user.
+  # in and out are allowed to be the same buffer, in may also be higher but still overlapping; in must
+  # have >= ilinebits*h bits, out must have >= olinebits*h bits, olinebits must be <= ilinebits
+  # also used to move bits after earlier such operations happened, e.g. in a sequence of reduced images from Adam7
+  # only useful if (ilinebits - olinebits) is a value in the range 1..7
+
+  let diff = ilinebits - olinebits
+  var
+    ibp = 0
+    obp = 0 # input and output bit pointers
+  for y in 0..h-1:
+    for x in 0..olinebits-1:
+      var bit = readBitFromReversedStream(ibp, input)
+      setBitOfReversedStream(obp, output, bit)
+    inc(ibp, diff)
+
+# Outputs various dimensions and positions in the image related to the Adam7 reduced images.
+# passw: output containing the width of the 7 passes
+# passh: output containing the height of the 7 passes
+# filter_passstart: output containing the index of the start and end of each
+# reduced image with filter bytes
+# padded_passstart output containing the index of the start and end of each
+# reduced image when without filter bytes but with padded scanLines
+# passstart: output containing the index of the start and end of each reduced
+# image without padding between scanLines, but still padding between the images
+# w, h: width and height of non-interlaced image
+# bpp: bits per pixel
+# "padded" is only relevant if bpp is less than 8 and a scanLine or image does not
+# end at a full byte
+proc adam7PassValues*(pass: var PNGPass, w, h, bpp: int) =
+  # the passstart values have 8 values:
+  # the 8th one indicates the byte after the end of the 7th (= last) pass
+
+  # calculate width and height in pixels of each pass
+  for i in 0..6:
+    pass.w[i] = (w + ADAM7_DX[i] - ADAM7_IX[i] - 1) div ADAM7_DX[i]
+    pass.h[i] = (h + ADAM7_DY[i] - ADAM7_IY[i] - 1) div ADAM7_DY[i]
+    if pass.w[i] == 0: pass.h[i] = 0
+    if pass.h[i] == 0: pass.w[i] = 0
+
+  pass.filterStart[0] = 0
+  pass.paddedStart[0] = 0
+  pass.start[0] = 0
+  for i in 0..6:
+    # if passw[i] is 0, it's 0 bytes, not 1 (no filtertype-byte)
+    pass.filterStart[i + 1] = pass.filterStart[i]
+    if (pass.w[i] != 0) and (pass.h[i] != 0):
+      pass.filterStart[i + 1] += pass.h[i] * (1 + (pass.w[i] * bpp + 7) div 8)
+    # bits padded if needed to fill full byte at end of each scanLine
+    pass.paddedStart[i + 1] = pass.paddedStart[i] + pass.h[i] * ((pass.w[i] * bpp + 7) div 8)
+    # only padded at end of reduced image
+    pass.start[i + 1] = pass.start[i] + (pass.h[i] * pass.w[i] * bpp + 7) div 8
+
+# input: Adam7 interlaced image, with no padding bits between scanLines, but between
+# reduced images so that each reduced image starts at a byte.
+# output: the same pixels, but re-ordered so that they're now a non-interlaced image with size w*h
+# bpp: bits per pixel
+# output has the following size in bits: w * h * bpp.
+# input is possibly bigger due to padding bits between reduced images.
+# output must be big enough AND must be 0 everywhere if bpp < 8 in the current implementation
+# (because that's likely a little bit faster)
+# NOTE: comments about padding bits are only relevant if bpp < 8
+proc adam7Deinterlace*(output: var openArray[byte], input: openArray[byte], w, h, bpp: int) =
+  var pass: PNGPass
+  adam7PassValues(pass, w, h, bpp)
+
+  if bpp >= 8:
+    for i in 0..6:
+      let byteWidth = bpp div 8
+      for y in 0..<pass.h[i]:
+        for x in 0..<pass.w[i]:
+          let inStart  = pass.start[i] + (y * pass.w[i] + x) * byteWidth
+          let outStart = ((ADAM7_IY[i] + y * ADAM7_DY[i]) * w + ADAM7_IX[i] + x * ADAM7_DX[i]) * byteWidth
+          for b in 0..<byteWidth:
+            output[outStart + b] = input[inStart + b]
+  else: # bpp < 8: Adam7 with pixels < 8 bit is a bit trickier: with bit pointers
+    for i in 0..6:
+      let ilinebits = bpp * pass.w[i]
+      let olinebits = bpp * w
+      for y in 0..<pass.h[i]:
+        for x in 0..<pass.w[i]:
+          var ibp = (8 * pass.start[i]) + (y * ilinebits + x * bpp)
+          var obp = (ADAM7_IY[i] + y * ADAM7_DY[i]) * olinebits + (ADAM7_IX[i] + x * ADAM7_DX[i]) * bpp
+          for b in 0..<bpp:
+            let bit = readBitFromReversedStream(ibp, input)
+            # note that this function assumes the out buffer is completely 0, use setBitOfReversedStream otherwise
+            setBitOfReversedStream0(obp, output, bit)
+
+#input: non-interlaced image with size w*h
+#output: the same pixels, but re-ordered according to PNG's Adam7 interlacing, with
+# no padding bits between scanlines, but between reduced images so that each
+# reduced image starts at a byte.
+#bpp: bits per pixel
+#there are no padding bits, not between scanlines, not between reduced images
+#in has the following size in bits: w * h * bpp.
+#output is possibly bigger due to padding bits between reduced images
+#NOTE: comments about padding bits are only relevant if bpp < 8
+proc adam7Interlace*(output: var openArray[byte], input: openArray[byte], w, h, bpp: int) =
+  var pass: PNGPass
+  adam7PassValues(pass, w, h, bpp)
+
+  if bpp >= 8:
+    for i in 0..6:
+      let byteWidth = bpp div 8
+      for y in 0..<pass.h[i]:
+        for x in 0..<pass.w[i]:
+          let inStart = ((ADAM7_IY[i] + y * ADAM7_DY[i]) * w + ADAM7_IX[i] + x * ADAM7_DX[i]) * byteWidth
+          let outStart = pass.start[i] + (y * pass.w[i] + x) * byteWidth
+          for b in 0..<byteWidth:
+            output[outStart + b] = input[inStart + b]
+  else: # bpp < 8: Adam7 with pixels < 8 bit is a bit trickier: with bit pointers
+    for i in 0..6:
+      let ilinebits = bpp * pass.w[i]
+      let olinebits = bpp * w
+      for y in 0..<pass.h[i]:
+        for x in 0..<pass.w[i]:
+          var ibp = (ADAM7_IY[i] + y * ADAM7_DY[i]) * olinebits + (ADAM7_IX[i] + x * ADAM7_DX[i]) * bpp
+          var obp = (8 * pass.start[i]) + (y * ilinebits + x * bpp)
+          for b in 0..<bpp:
+            let bit = readBitFromReversedStream(ibp, input)
+            setBitOfReversedStream(obp, output, bit)