Sending image data to ESP over HTTP - Advice on approach

Using Arduino Project Guidance
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Hey there!

I am currently working on a project using an ESP32. In this project, I am requesting image data from a server. The image itself is 480x800 pixels. Each pixel has one of three values (red, black, white).

When sending an HTTP request to the server, and getting the image data as a response, I noticed, that I need to use the available resources on the ESP in a smart way, since simply requesting the raw image data seemed to require more than the available resources on the ESP32 (I received a code 200 responses but empty response string). When shortening down the response string, for example using a compression algorithm, I manage to receive the full response string. However, I then noticed, that decompression seems to be slow to do on the ESP32. Below you can see an overview of the different approaches I used to modify the sent data:

  1. Using no compression
    • Deconstructing the base image (Red, black, white) into two images (red, white <-> black, white) as bytearray
    • Base64-Encoding of the two bytearrays
      Response-size: 125 KB
  2. Using LZMA compression algorithm
    • Deconstructing the base image (Red, black, white) into two images (red, white <-> black, white) as bytearray
    • LZMA compression of the two bytearrays
    • Base64-Encoding of the two compressed variables
      Response-size: 5,8 KB

While the compression is great and helps a lot to save space in the request, I didn't find any Arduino/ESP library, that implemented LZMA decompression while also seeming widely accepted/well maintained.

I can adjust the server code to implement any common compression method, or possibly also implement a custom-made one since there are only 3 possible values for each pixel. The server-side code is written in Python.

How would you go about setting up the general software on the ESP and on the server for requesting the image data?

2

One of my ESP32's does the image transfer thing using FTP.

Might or might be a solution that you can use.

1 Like
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There is no need to use base64 encoding, you can send your image data as binary. a 480x800x2 image would be about 94kB

1 Like
4

Thanks for the suggestion, I will try that!

From your experience, would you say that it should be no problem to receive a 94KB large response with the ESP32?

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I've never used an ESP32 so can't say...

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What are you going to do with the image once you have it?

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I do not see there being an issue receiving a 100K image file.

If the image file is to exceed 100K, then use a ESP32 WROVER and put the receive buffer into PSRAM. I get a little less then 4MB of download space under the Arduino IDE with PSRAM. If more PSRAM access is needed use the ESPRESSIFF IDF.

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