Direct read data from a file png - png

Question

is required to read data from a binary file without loading them in Bitmap because it is too much, more than 20000x20000 pixels, I need to open a file, one line at a time to read a file for processing. found an example for reading BMP, can not understand how in the same way to get data from PNG.
byte[] B = File.ReadAllBytes(filename);
GCHandle GCH = GCHandle.Alloc(B, GCHandleType.Pinned);
IntPtr Scan0 = (IntPtr)((int)(GCH.AddrOfPinnedObject()) + 54);
int W = Marshal.ReadInt32(Scan0, -36);
int H = Marshal.ReadInt32(Scan0, -32);
Bitmap Bmp = new Bitmap(W, H, 4 * W, PixelFormat.Format32bppArgb, Scan0);
GCH.Free();
return Bmp;
Language C#

Answer 1

I found a library (PNGChunkParser) with parsing blocks APG has received all the blocks that are in the file, I found a 21 unit Idate, but trying to paint them 50 lines, to be not the right picture:
byte[] B = File.ReadAllBytes(filename);
List<byte> tmpb = new List<byte>();
using (MemoryStream stream = new MemoryStream(B))
{
PNGChunk[] chunks = PNGChunkParser.ChunksFromStream(stream).ToArray();
foreach (PNGChunk item in chunks)
{
if (item.TypeString == "IDAT")
{
PNGChunk idatChunk = item;
foreach (byte s in idatChunk.Data)
{
tmpb.Add(s);
}
}
}
}
var size_png = ImageHelper.GetDimensions(filename);
GetConturPic(tmpb.ToArray(), size_png.Width, 50,PixelFormat.Format32bppArgb);
private void GetConturPic(byte[] data, int w, int h, PixelFormat pixel_format)
{
int index;
int stride = GetStride(w, pixel_format);
Bitmap bm = new Bitmap(w, h);
Color fm = new Color();
try
{
for (int y = 0; y < h; y++)
{
for (int x = 0; x < w; x++)
{
index = y * stride + 4 * x;
fm = GetPixelColor(data, w, h, x, y,
System.Drawing.Bitmap.GetPixelFormatSize(pixel_format));
bm.SetPixel(x, y, fm);
}
pictureBox1.Image = bm;
pictureBox1.Refresh();
}
}
catch (Exception ex)
{
listBox1.Items.Add(ex.Message);
}
}
public Color GetPixelColor(byte[] Pixels, int w, int h, int x, int y, int depth)
{
Color clr = Color.Empty;
// Get color components count
int cCount = depth / 8;
// Get start index of the specified pixel
int i = ((y * w) + x) * cCount;
if (i > Pixels.Length - cCount)
throw new IndexOutOfRangeException();
byte b, g, a, r, c;
switch (depth)
{
case 32:
b = Pixels[i];
g = Pixels[i + 1];
r = Pixels[i + 2];
a = Pixels[i + 3]; // a
clr = Color.FromArgb(a, b, g, r);
break;
case 24:
b = Pixels[i];
g = Pixels[i + 1];
r = Pixels[i + 2];
clr = Color.FromArgb(b, g, r);
break;
case 8:
c = Pixels[i];
clr = Color.FromArgb(c, c, c);
break;
}
return clr;
}
help what need to do to get 50 lines of image ?