update readme.md and add savePNG

nimPNG.nim

@@ -2937,27 +2937,22 @@ proc writeChunks*(png: PNG, s: Stream) =
     s.write chunk.data
     s.writeInt32BE cast[int](chunk.crc)
 
+proc savePNG*(fileName, input: string, colorType: PNGcolorType, bitDepth, w, h: int): bool =
+  try:
+    var png = encodePNG(input, colorType, bitDepth, w, h)
+    var s = newFileStream(fileName, fmWrite)
+    png.writeChunks s
+    s.close()
+    result = true
+  except:
+    debugEcho getCurrentExceptionMsg()
+    result = false
+    
 proc savePNG32*(fileName, input: string, w, h: int): bool =
-  try:
+  result = savePNG(fileName, input, LCT_RGBA, 8, w, h)
-    var png = encodePNG(input, LCT_RGBA, 8, w, h)
+  
-    var s = newFileStream(fileName, fmWrite)
-    png.writeChunks s
-    s.close()
-    result = true
-  except:
-    debugEcho getCurrentExceptionMsg()
-    result = false
-
 proc savePNG24*(fileName, input: string, w, h: int): bool =
-  try:
+  result = savePNG(fileName, input, LCT_RGB, 8, w, h)
-    var png = encodePNG(input, LCT_RGB, 8, w, h)
-    var s = newFileStream(fileName, fmWrite)
-    png.writeChunks s
-    s.close()
-    result = true
-  except:
-    debugEcho getCurrentExceptionMsg()
-    result = false
 
 proc getFilterTypesInterlaced(png: PNG): seq[string] =
   var header = PNGHeader(png.getChunk(IHDR))

nimPNG.nimble

@@ -1,6 +1,6 @@
 [Package]
 name          = "nimPNG"
-version       = "0.1.1"
+version       = "0.1.2"
 author        = "Andri Lim"
 description   = "PNG encoder and decoder"
 license       = "MIT"

readme.md

@@ -1,6 +1,5 @@
 #nimPNG
-Portable Network Graphics Encoder and Decoder written in Nim
+Portable Network Graphics Encoder and Decoder written in Nim store lossless image with good compression
-store lossless image with good compression
 
 all PNG standard color mode are supported:
 
@@ -43,5 +42,42 @@ Supported color conversions:
 - removing alpha channel
 - higher to smaller bitdepth, and vice versa
 
-###Feature planned:
+###Planned Feature(s):
 - streaming for progressive loading
+
+##Basic Usage
+```nimrod
+import nimPNG
+
+let png = loadPNG32("image.png")
+#is equivalent to:
+#let png = loadPNG("image.png", LCT_RGBA, 8)
+#will produce rgba pixels:
+#png.width -> width of the image
+#png.height -> height of the image
+#png.data -> pixels data in RGBA format
+```
+
+if you already have the whole file in memory
+let png = decodePNG32(raw_bytes)
+will do the same as above
+
+other variants:
+loadPNG24 -> will produce pixels in RGB format 8 bpp
+decodePNG24 -> load png from memory instead of file
+
+to create PNG:
+savePNG32("output.png", rgba_pixels, width, height)
+or savePNG24
+encodePNG32(rgba_pixels, width, height)
+or encodePNG24
+
+use **loadPNG** or **savePNG** if you need specific input/output format by supplying supported **colorType** and **bitDepth** information. Use **encodePNG** or **decodePNG** to do in memory encoding/decoding by supplying desired colorType and bitDepth information
+
+pixels are stored as raw bytes using Nim's string as container. 
+r1,g1,b1,a1,r2,g2,b2,a1,...,rn,gn,bn,an   -> RGBA format 8 bit
+r1,g1,b1,r2,g2,b2,...,rn,gn,bn   -> RGB format 8 bit
+grey1,grey2,grey3, ..., greyn  -> GREY format 8 bit
+grey1,alpha1,grey2,alpha2,...,greyn,alphan  -> GREY ALPHA format 8 bit
+
+