Returns true if the Read/Write Enabled checkbox was checked when the texture was imported; otherwise returns false. For a dynamic Texture created from script, always returns true. For additional information, see TextureImporter.isReadable.
To use Texture2D.GetPixel, Texture2D.GetPixels and similar functions, the isReadable property must be set to true. If you call these functions on a Texture on which the the isReadable property is not set to true, an exception is thrown.