Memory need on a bitmap stream

It didn't solved the problem but thx. The memmory is still growing, just slow but it is. I have no idea for this phenomenom. I have allready tried to convert the colors in int array and convert it back before Setpixel, but without effort, the same situation.
 

Try using block like this, it should solve memory leak issue.

I found a way, how to display the images without flickering. But the momory problem seems to came not from memspace reservation for the bitmap.

I have wondered when i found a big difference between :
bmp.SetPixel(x, y, Color.FromArgb(bCol, bCol, bCol)); // no mem growing
and
bmp.SetPixel(x, y, colorList[bCol]);  // continuously  mem growing

bCol range is 0 - 255. colorList is a list of assigned colors for each grayscale value, will be generated once while FormLoad.

List colorList = new List();

public void get_color_list()
        {
            Bitmap im1 = new Bitmap("C:\\ims_data\\Temp\\pal.png");
            Bitmap bmp= new Bitmap(im1, 55, 255);

            for (int j = 0; j < bmp.Height; j++)
            {
                Color pixelColor = bmp.GetPixel(0, j);
                colorList.Insert(j, pixelColor);
            }
              
            im1.Dispose();
            bmp.Dispose();
        }

What could be wrong if I just refer to the color in a list? Why do this result i small memory leaks?