Question

I am trying to determine if a 1BPP indexed TIFF image is using a white pixel or black pixel. To check if my code was correct , I made the application draw the same image it proccessed onto a new image. This is when I noticed some problems and I have beem beating my head trying to figure it out.

I am pretty sure it has something to do with my bitwise check!

origninal image

Processed Image

Test project can be downloaded at http://www.unclickable.net/code/tiffTest.zip
unsafe
{
//flipStartPoint

                int y;
                for (y = 0; y < tiffSource.Height; y++)
                {
                    var Column = (byte*)tiffSource.GetScanlinePointer(y);
                    int x;
                    for (x = 0; x < (tiffSource.Width / 8); x++)
                    {
                        int xm = x * 8;
                        byte b = Column[xm];


                        if (b > 0)
                        {

                                for (int Z = 0; Z < 8; Z++)
                                {


                                    if (((b & (128 >> Z)) != 0))
                                    {
                                        if (lowisWhite)
                                        {
                                            image1.SetPixel((xm + Z), y, Color.FromArgb(0, 255, 255,255));
                                        }

                                    }
                                    else
                                    {
                                        if (!lowisWhite)
                                        {

                                            image1.SetPixel((xm + Z), y, Color.FromArgb(0, 255,255, 255));
                                        }
                                    }

                                }

                        }
                        else
                        {
                            if (!lowisWhite)
                            {
                                for (int Z = 0; Z < 8; Z++)
                                {


                                    image1.SetPixel((xm + Z), y, Color.FromArgb(0, 255, 255, 255));

                                }
                            }
                        }
                    }
                }
            }

Answer 1

User,

this seems to do the trick, the code below. Remember this for the rest of your life: if you hope any response from a discussion board, the code should be cuttable and pastable with all using’s and declarations included!

Now I didn’t include the rest of the partial class because it is automatically generated by c# when you start a project. You make people jump thru hoops they are not going to work for you.

I could not find the strange GetScanLine function. If is from another library, what is that and what’s the quickest way I could test with it?

Before running this I saved your image in c:\temp\bw.tif, making sure to set it as 1bpp in MS Paint. I also set a breakpoint after the load of the file to prove that the .ImageFormat property was 1bpp. Result appears in c:\temp\out.jpg.

Looks like there are several reasons why the original failed. The way you are doing x*8, or not, seems doubled or curious. I took a different approach to go straight from x and y to the pixel.

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    unsafe 
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Bitmap tiffSource = new Bitmap("c:\\temp\\bw.tif");
            Bitmap image1 = new Bitmap(tiffSource.Width, tiffSource.Height);

            BitmapData d = tiffSource.LockBits(
                 new Rectangle(new Point(0, 0), tiffSource.Size),
                 ImageLockMode.ReadOnly,tiffSource.PixelFormat);
            for (int y = 0; y < tiffSource.Height; y++)
            {
                byte* Column = (byte*)d.Scan0 + y*d.Stride;

                for (int x = 0; x < (tiffSource.Width ); x++)
                    if ((Column[(int)(x / 8)] & (128 >> (x % 8))) !=0   )
                        image1.SetPixel((x), y, Color.FromArgb(0, 0, 0, 0));
                    else
                        image1.SetPixel((x), y, Color.FromArgb(0, 255, 255, 255));
            }
            tiffSource.UnlockBits(d);
            image1.Save("c:\\temp\\out.jpg");
        }
    }
}