Tiled Map Display Problem

Hi,

I load a tiled map made by Tiled Map Editor, but there are black edges around each tile, how to fix it?

The script I used is similar to UniTMX, here is the generating uv part:

     private List<Vector2> GenUV (ref TileSet tileset)
     {
 
         List<Vector2> uv = new List<Vector2> (); 
         int horizontalCellCount = (tileset.SourceWidth - tileset.Margin) / (tileset.TileWidth + tileset.Spacing);
         int verticalCellCount = (tileset.SourceHeight - tileset.Margin) / (tileset.TileHeight + tileset.Spacing);        
         float cellWidth = ((float)(tileset.TileWidth) / tileset.SourceWidth);
         float cellHeight = ((float)(tileset.TileHeight) / tileset.SourceHeight);
         int dataValue;
         for (int y = 0; y < Height; y++)
         {
             for (int x = 0; x < Width; x++)
             {
                 if (Data[y, x] != 0)
                 {
                     dataValue = Data[y, x] - tileset.FirstGID;
                     int posY = dataValue / verticalCellCount;
                     int posX = dataValue % horizontalCellCount;
                     float u = ((float)(tileset.Margin + (tileset.TileWidth + tileset.Spacing) * posX) / tileset.SourceWidth);
                     float v = 1.0f - ((float)(tileset.Margin + (tileset.TileHeight + tileset.Spacing) * posY) / tileset.SourceHeight);
                     uv.AddRange (new Vector2[] {
                         new Vector2 (u, v),
                         new Vector2 (u, v - cellHeight),
                         new Vector2 (u + cellWidth, v),
                         new Vector2 (u + cellWidth, v - cellHeight),                                                                
                     });
                 }
             }
         }
         return uv;
     }

My tileset has 4 pixels for both spacing and margin.

Thank you for your help.