图集像素格式可以选择，引擎能自动识别？如何手动设置？
--pixelFormat Mono | MonoLSB | Indexed8 | RGB32 |
ARGB32 | ARGB32_Premultiplied | RGB16
| ARGB8565_Premultiplied | RGB666 |
ARGB6666_Premultiplied | RGB555 |
ARGB8555_Premultiplied | RGB888 |
RGB444 | ARGB4444_Premultiplied |
RGBX8888 | RGBA8888 |
RGBA8888_Premultiplied | BGR30 |
A2BGR30_Premultiplied | RGB30 |
A2RGB30_Premultiplied | Alpha8 |
Grayscale8, default ARGB32
