0 fps on Histogram

[PluemXXE]

Describe the bug A clear and concise description of what the bug is.

While I do nothing with maixpy ​​ide histogram is 0 fps, but when I click something on maixpy ​​ide the fps it is greater than 0.

Please complete the following information

• IDE version: [e.g. 0.2.5]
• Firmware version: [e.g. 0.6.2]
• Board: [e.g. Maix Amigo]
• OS: [e.g.mac os]