Font not well rendered with freetype and Opengl ES 2 (IPhone device)

[admin]

I'm using freetype for writing text in an IPhone device, the result are rare. As you can see in the image same characters(like 'b', 'n' or 'u') aren't rendered equally.

The texture is always the same. Any idea where is the problem or what's going on?

<a href="http://craneossgd.files.wordpress.com/2011/10/image_freetype1.png" rel="nofollow">http://craneossgd.files.wordpress.com/2011/10/image_freetype1.png</a>

Code:

FT_New_Face(getFTLibrary(), _filename, 0, &(_face))
FT_Select_Charmap( _face, FT_ENCODING_UNICODE );
FT_Set_Char_Size( _face, _pt<<6,_pt<<6, _dpi, _dpi);
for (i=0; i<255; i++)
{
    if (!createGlyphTexture(i))
    {
        clean();
    }
}
.....

createGlyphTexture(unsigned char ch){
    ....
    FT_Load_Glyph(_face, FT_Get_Char_Index(_face,ch), FT_LOAD_DEFAULT)
    FT_Get_Glyph(_face->glyph, &glyph)
    ....
    // *** Transform glyph to bitmap
    FT_Glyph_To_Bitmap(&glyph, FT_RENDER_MODE_NORMAL, 0, 1);

    // *** Get bitmap and glyph data
    bitmap_glyph = (FT_BitmapGlyph)glyph;
    bitmap = bitmap_glyph->bitmap;
    // ***
    width = pow2(bitmap.width);
    height = pow2(bitmap.rows);

    // *** Alloc memory for texture
    expanded_data = (GLubyte *)malloc( sizeof(GLubyte)*2*width*height );
    for (j=0; j<height;j++)
{
    for (i=0; i<width; i++)
    {
        if ( (i>=(CRuint)bitmap.width) || (j>=(CRuint)bitmap.rows) ){
            expanded_data[2*(i+j*width)] = 0;
            expanded_data[2*(i+j*width)+1] = 0;
        } else {
            expanded_data[2*(i+j*width)] = bitmap.buffer[i+bitmap.width*j];
            expanded_data[2*(i+j*width)+1] = bitmap.buffer[i+bitmap.width*j];
        }
    }
}
    // *** Load texture into memory
    glBindTexture(GL_TEXTURE_2D, _textures[ch]);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexImage2D(GL_LUMINANCE_ALPHA, width, height, 0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, expanded_data);
    ....
}

Thanks!!