ESP32-CAM for Computational Photography

H. G. Dietz
http://aggregate.org/hankd/

Department of Electrical and Computer Engineering
Center for Visualization & Virtual Environments
University of Kentucky, Lexington, KY 40506-0046

Initial release: March 4, 2021

This document should be cited using something like the bibtex entry:

@techreport{esp32cam20210304,
author={Henry Gordon Dietz},
title={{ESP32-CAM For Computational Photography}},
month={March},
year={2021},
institution={University of Kentucky},
howpublished={Aggregate.Org online technical report},
URL={http://aggregate.org/DIT/ESP32CAM/}
}

For quite some years now, I, Professor Hank Dietz, and my students have been using CHDK (Canon Hack Development Kit) to do evil things inside Canon PowerShot cameras. Those cameras generally start at around $80, and they provide quite good image quality with high resolution, but they aren't really very beefy computing systems: typically, they are dual-core ARMs at around 80MHz. They are also very difficult to pull apart; for example, removing the lens to use an interchangeable mount isn't really feasible.

In contrast, the $7 AI Thinker ESP32-CAM camera is only 2MP, but it's trivial to unscrew the lens. In a board just 27x40mm, it provides a 240MHz dual-core 32-bit Tensilica processor, 802.11 WiFi and BlueTooth as well as wired interfaces, a microSD slot, low power modes, etc.

ESP32-CAM Observations & References

• In general, the most useful collection of info about the ESP32-CAM is at Random Nerd Tutorials. ESP32-CAM AI-Thinker Pinout Guide: GPIOs Usage Explained provides a really great overview, including:
  
• There are two different OV2640 camera modules. They look very similar, but the older version is slightly larger and has a wider-angle lens. More importantly, the older version is in landscape orientation with the ESP32-CAM in what looks like the portrait orientation, whereas the newer one has the long dimension aligning with the long dimension of the board.
• Perhaps the single most annoying thing about the ESP32-CAM is the wild overloading of multiple functions to each I/O pin. This can easily lead to strange and inconsistent behaviors that would be unacceptable in a product, and yet the rules for pin use are essentially undocumented. For example, discusses undesirable interactions with the SD card interface. Fortunately, Pin Notes does a pretty good job of listing for each pin what issues might be encountered.
• Another random problem with the ESP32-CAM is that the brownout detection is a little too aggressive, triggering on power problems that are not sufficient to cause errors. That said, momentary power drain can be significant, and you probably want to use a 5V supply because reprogramming tends to fail at 3.3V. Even so, it is often appropriate to simply disable brownout detection using something like:

  #include "soc/soc.h"
  #include "soc/rtc_cntl_reg.h"
  
  WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0);
  

• Change ESP32-CAM OV2640 Camera Settings: Brightness, Resolution, Quality, Contrast, and More provides a nice overview of how to change various setting on the OV2640 camera by using sensor_t operations.
• FORMAT_RGB565 and FORMAT_RGB888 DO NOT WORK!!! provides a very detailed set of observations about PIXFORMAT changes not being effective using the sensor_t operations. This is unfortunately correct; format changes don't work after initialization of the camera, so don't waste time trying it. The best work-around is to capture PIXFORMAT_JPEG and use the img_converters.h functions to decode the JPEGs from the camera; it works well, but note that there isn't enough memory space for a 1600x1200 RGB888 image even in PSRAM. Note that you can get images as small as 160x120 by using FRAMESIZE_QQVGA.
• ESP32-CAM Video Streaming Server Connecting I2C and SPI Displays gives a reasonable overview, although I'll be releasing a much better way to drive an I2C OLED display for an EVF.

ESP32-CAM Useful Libraries

• I've created an Arduino driver library for LCLV like Adafruit 3627 and 3330 that works with most Arduino-compatibles, including ESP32-CAM.

The only thing set in stone is our name.