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The Image Transfer mode allows you to select an image and transmit it over BLE. The interface also offers a number of additional features for advanced users.

Data Format

Image data is sent from over BLE in the following format:

  • Single byte char “!” (0x21)
  • Single byte char 'I' (0x49)
  • Color space (uint8 16 for 16bits 565 or 24 for 24-bit 888)
  • Image width (uint16 little endian, 2 bytes)
  • Height (uint16 little endian, 2 bytes)
  • Pixel data encoded as "RGB 16bit 565” or "RGB 24-bit 888" depending on the Color Space selected
  • Single byte CRC

Choose Image

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Tap the Choose Image button to select an image from your device’s photo library or capture a new one from the camera. After selecting your image, use a pinch gesture to scale it for cropping within the white bounding box.

Bit Depth

This setting toggles between two color bit-depth settings: 16-bit & 24-bit. This value determines how many bits of data are used to represent each pixel’s color value. A higher value allows for a greater range of colors, but uses more data and time to transfer.

Resolution

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The Resolution setting allow you to choose from a list of preset image resolutions designed to fit common displays. Setting a resolution will update the selected image's pixellation as a preview.

Transfer Mode

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The Transfer Mode setting determines how often the app will require a confirmation response from the Bluefruit hardware before sending more data. Tapping the button offers three options:

  • Without Response (fastest, least reliable): App never waits for response before sending more data
  • With Response (slowest, most reliable): App always waits for response to before sending more data
  • Interleaved (customizable, varies): App sends a number of packets w/o response before sending one w response. The default value of 50 offers a nice middle ground between speed and reliability.
Example code written for Circuit Playground Bluefruit + TFT Gizmo is only compatible with default Transfer Mode of Interleaved [50:1]

Rotate & Send

The image can be rotated using the buttons on either side of the Send Image button.

Pressing Send Image will present a progress bar and begin sending data to the Bluefruit Hardware.

This guide was first published on Feb 20, 2015. It was last updated on 2020-10-20 06:51:45 -0400.
This page (Image Transfer) was last updated on Oct 24, 2020.