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samples: lib: pixel: show usage of the pixel library
The newly introduced lib/pixel features utilities that help composing video pipelines together for the purpose of stream processing, as well as debug utilities. Signed-off-by: Josuah Demangeon <me@josuah.net>
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‎samples/lib/lib.rst

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.. zephyr:code-sample-category:: lib
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:name: Libraries
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:show-listing:
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:live-search:
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These samples demonstrate how to use the libraries present in Zephyr.

‎samples/lib/pixel/pixel.rst

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.. zephyr:code-sample-category:: lib_pixel
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:name: Pixel Library
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:show-listing:
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:live-search:
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These samples demonstrate how to use the Pixel processing library of Zephyr.
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These samples can be used as starting point for test benches that print an input image,
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perform some custom processing, and print the color image back along with the logs directly
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on the terminal.
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The color rendering of the ``truecolor`` printing functions will be accurate RGB output.
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This helps debugging individual functions before integrating it into a larger streams.

‎samples/lib/pixel/print/CMakeLists.txt

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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(pixel)
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target_sources(app PRIVATE src/main.c)

‎samples/lib/pixel/print/README.rst

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.. zephyr:code-sample:: lib_pixel_print
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:name: Pixel Printiing Library
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Print images on the console.
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Overview
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********
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A sample showcasing how to make use of the pixel library to visualize an image or histogram data
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by printing it out on the console using `ANSI escape codes`_.
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This allow interleaving debug logs with small previews of the image as a way to debug image data.
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.. _ANSI escape codes: https://en.wikipedia.org/wiki/ANSI_escape_code
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Building and Running
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********************
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This application can be built and executed on QEMU as follows:
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.. zephyr-app-commands::
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:zephyr-app: samples/lib/pixel/print
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:host-os: unix
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:board: native_sim
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:goals: run
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:compact:
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To build for another board, change "native_sim" above to that board's name.
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Sample Output
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=============
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.. code-block:: console

‎samples/lib/pixel/print/prj.conf

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CONFIG_PIXEL=y
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CONFIG_ASSERT=y
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CONFIG_LOG=y
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# Required to make sure the test harnesses catch the log output
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CONFIG_LOG_MODE_IMMEDIATE=y

‎samples/lib/pixel/print/sample.yaml

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sample:
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description: Pixel Print sample, print images in the terminal for debug purpose
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name: pixel print
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common:
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min_ram: 32
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tags: pixel
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integration_platforms:
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- native_sim
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harness: console
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harness_config:
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type: one_line
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regex:
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- "truecolor:"
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- "256color:"
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- "hexdump:"
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- "histogram"
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tests:
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sample.pixel.print:
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tags: pixel

‎samples/lib/pixel/print/src/main.c

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/*
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* Copyright (c) 2025 tinyVision.ai Inc.
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <stdint.h>
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#include <zephyr/sys/util.h>
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#include <zephyr/pixel/print.h>
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#include <zephyr/logging/log.h>
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LOG_MODULE_REGISTER(app, LOG_LEVEL_INF);
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static uint8_t rgb24frame[16 * 32 * 3];
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void print_image(void)
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{
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const uint8_t beg[] = {0x00, 0x70, 0xc5};
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const uint8_t end[] = {0x79, 0x29, 0xd2};
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/* Generate an image with a gradient of the two colors above */
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for (size_t i = 0, size = sizeof(rgb24frame); i + 3 <= size; i += 3) {
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rgb24frame[i + 0] = (beg[0] * (size - i) + end[0] * i) / size;
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rgb24frame[i + 1] = (beg[1] * (size - i) + end[1] * i) / size;
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rgb24frame[i + 2] = (beg[2] * (size - i) + end[2] * i) / size;
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}
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LOG_INF("Printing the gradient #%02x%02x%02x -> #%02x%02x%02x",
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beg[0], beg[1], beg[2], end[0], end[1], end[2]);
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LOG_INF("hexdump:");
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pixel_print_rgb24frame_hex(rgb24frame, sizeof(rgb24frame), 16, 32);
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LOG_INF("truecolor:");
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pixel_print_rgb24frame_truecolor(rgb24frame, sizeof(rgb24frame), 16, 32);
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LOG_INF("256color:");
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pixel_print_rgb24frame_256color(rgb24frame, sizeof(rgb24frame), 16, 32);
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}
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void print_histogram(void)
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{
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static const uint16_t rgb24hist[] = {
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9, 4, 7, 1, 0, 5, 1, 0, 0, 2, 2, 3, 0, 1, 3, 0,
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7, 6, 5, 1, 1, 4, 2, 0, 1, 2, 3, 4, 1, 1, 2, 2,
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8, 4, 7, 4, 2, 3, 1, 2, 2, 2, 2, 2, 0, 0, 1, 1,
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};
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static const uint16_t y8hist[] = {
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8, 5, 6, 2, 1, 4, 1, 1, 1, 2, 3, 3, 1, 1, 2, 1,
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};
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LOG_INF("Printing a histogram of %zu RGB buckets", ARRAY_SIZE(rgb24hist));
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pixel_print_rgb24hist(rgb24hist, ARRAY_SIZE(rgb24hist), 8);
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LOG_INF("Printing a histogram of %zu Y (luma) buckets", ARRAY_SIZE(y8hist));
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pixel_print_y8hist(y8hist, ARRAY_SIZE(y8hist), 8);
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}
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int main(void)
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{
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print_image();
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print_histogram();
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return 0;
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}

‎samples/lib/pixel/resize/CMakeLists.txt

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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(pixel)
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target_sources(app PRIVATE src/main.c)

‎samples/lib/pixel/resize/README.rst

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.. zephyr:code-sample:: lib_pixel_resize
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:name: Pixel Resizing Library
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Resize an image using subsampling.
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Overview
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********
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A sample showcasing how to make use of the pixel library to resize an input image to a smaller or
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bigger output image, using the subsampling method. This helps generating a smaller preview of an
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input image.
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The input and output are printed as preview images on the console.
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Building and Running
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********************
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This application can be built and executed on the native simulator as follows:
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.. zephyr-app-commands::
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:zephyr-app: samples/lib/pixel/resize
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:host-os: unix
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:board: native_sim
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:goals: run
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:compact:
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To build for another board, change "native_sim" above to that board's name.
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Sample Output
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=============
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.. code-block:: console

‎samples/lib/pixel/resize/prj.conf

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CONFIG_PIXEL=y
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CONFIG_ASSERT=y
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CONFIG_LOG=y
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# Required to make sure the test harnesses catch the log output
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CONFIG_LOG_MODE_IMMEDIATE=y

‎samples/lib/pixel/resize/sample.yaml

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sample:
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description: Pixel Resize sample, down-scale/up-scale an image
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name: pixel resize
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common:
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min_ram: 32
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tags: pixel
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integration_platforms:
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- native_sim
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harness: console
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harness_config:
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type: one_line
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regex:
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- "output image, bigger,"
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- "output image, smaller,"
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tests:
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sample.pixel.resize:
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tags: pixel

‎samples/lib/pixel/resize/src/main.c

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/*
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* Copyright (c) 2025 tinyVision.ai Inc.
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <stdint.h>
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#include <zephyr/sys/util.h>
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#include <zephyr/pixel/resize.h>
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#include <zephyr/pixel/print.h>
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#include <zephyr/logging/log.h>
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LOG_MODULE_REGISTER(app, LOG_LEVEL_INF);
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static void gradient(uint8_t *rgb24buf, size_t size, const uint8_t beg[3], const uint8_t end[3])
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{
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for (int i = 0; i + 3 <= size; i += 3) {
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rgb24buf[i + 0] = (beg[0] * (size - i) + end[0] * i) / size;
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rgb24buf[i + 1] = (beg[1] * (size - i) + end[1] * i) / size;
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rgb24buf[i + 2] = (beg[2] * (size - i) + end[2] * i) / size;
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}
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}
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static uint8_t rgb24frame0[32 * 16 * 3];
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static uint8_t rgb24frame1[120 * 20 * 3];
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static uint8_t rgb24frame2[10 * 10 * 3];
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int main(void)
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{
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const uint8_t beg[] = {0x00, 0x70, 0xc5};
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const uint8_t end[] = {0x79, 0x29, 0xd2};
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LOG_INF("input image, 32x16, %zu bytes:", sizeof(rgb24frame0));
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gradient(rgb24frame0, sizeof(rgb24frame0), beg, end);
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pixel_print_rgb24frame_truecolor(rgb24frame0, sizeof(rgb24frame0), 32, 16);
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LOG_INF("output image, bigger, 120x16, %zu bytes:", sizeof(rgb24frame1));
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pixel_subsample_rgb24frame(rgb24frame0, 32, 16, rgb24frame1, 120, 20);
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pixel_print_rgb24frame_truecolor(rgb24frame1, sizeof(rgb24frame1), 120, 20);
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LOG_INF("output image, smaller, 10x10, %zu bytes:", sizeof(rgb24frame2));
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pixel_subsample_rgb24frame(rgb24frame0, 32, 16, rgb24frame2, 10, 10);
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pixel_print_rgb24frame_truecolor(rgb24frame2, sizeof(rgb24frame2), 10, 10);
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return 0;
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}

‎samples/lib/pixel/stats/CMakeLists.txt

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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(pixel)
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target_sources(app PRIVATE src/main.c)

‎samples/lib/pixel/stats/README.rst

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.. zephyr:code-sample:: lib_pixel_stats
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:name: Pixel Statistics Library
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Collect statistics of an image.
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Overview
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********
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A sample showcasing how to make use of the pixel library to collect statistics of an input image
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buffer and display both the image and statistics out on the console.
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Building and Running
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********************
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This application can be built and executed on the native simulator as follows:
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.. zephyr-app-commands::
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:zephyr-app: samples/lib/pixel/stats
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:host-os: unix
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:board: native_sim
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:goals: run
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:compact:
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To build for another board, change "native_sim" above to that board's name.
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Sample Output
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=============
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.. code-block:: console

‎samples/lib/pixel/stats/prj.conf

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CONFIG_PIXEL=y
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CONFIG_ASSERT=y
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CONFIG_LOG=y
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# Required to make sure the test harnesses catch the log output
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CONFIG_LOG_MODE_IMMEDIATE=y

‎samples/lib/pixel/stats/sample.yaml

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sample:
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description: Pixel Stats sample, collect statistics of an input buffer
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name: pixel stats
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common:
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min_ram: 32
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tags: pixel
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integration_platforms:
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- native_sim
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harness: console
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harness_config:
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type: one_line
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regex:
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- "RGB histogram of the image"
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- "RGB channel averages of the image"
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tests:
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sample.pixel.stats:
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tags: pixel

‎samples/lib/pixel/stats/src/main.c

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/*
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* Copyright (c) 2025 tinyVision.ai Inc.
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <stdint.h>
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#include <zephyr/sys/util.h>
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#include <zephyr/pixel/stats.h>
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#include <zephyr/pixel/print.h>
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#include <zephyr/logging/log.h>
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LOG_MODULE_REGISTER(app, LOG_LEVEL_INF);
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#define NVAL 100
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static const uint8_t image_rgb24[20 * 4 * 3] = {
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0x47, 0x84, 0xee, 0x46, 0x84, 0xee, 0x47, 0x84, 0xee, 0x46, 0x83, 0xee, 0x47, 0x84, 0xee,
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0x78, 0xaa, 0xec, 0x74, 0xb2, 0xe0, 0x67, 0xaa, 0xdd, 0x78, 0xb2, 0xef, 0x39, 0x8c, 0xf1,
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0x3a, 0x8c, 0xf2, 0x39, 0x8b, 0xf1, 0x3a, 0x8b, 0xf1, 0x3a, 0x8b, 0xf1, 0x3a, 0x8b, 0xf1,
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0x3a, 0x8b, 0xf1, 0x3b, 0x8b, 0xf1, 0x3b, 0x8b, 0xf1, 0x3b, 0x8b, 0xf1, 0x3b, 0x8a, 0xf1,
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0x47, 0x82, 0xed, 0x47, 0x82, 0xed, 0x47, 0x82, 0xee, 0x47, 0x82, 0xed, 0x47, 0x82, 0xed,
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0x47, 0x82, 0xed, 0x5d, 0x93, 0xed, 0x5f, 0x9d, 0xeb, 0x3a, 0x8a, 0xf1, 0x3a, 0x8a, 0xf0,
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0x3a, 0x8a, 0xf1, 0x3a, 0x8a, 0xf0, 0x3b, 0x8a, 0xf0, 0x3b, 0x8a, 0xf0, 0x3b, 0x8a, 0xf0,
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0x3b, 0x89, 0xf0, 0x3b, 0x8a, 0xf0, 0x3b, 0x89, 0xf0, 0x3c, 0x89, 0xf0, 0x3c, 0x89, 0xf0,
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0x49, 0x82, 0xee, 0x49, 0x82, 0xed, 0x49, 0x82, 0xee, 0x48, 0x82, 0xed, 0x49, 0x82, 0xee,
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0x49, 0x82, 0xed, 0x73, 0x92, 0xe9, 0x50, 0x65, 0xd4, 0x4c, 0x93, 0xf2, 0x3c, 0x8a, 0xf1,
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0x3c, 0x8a, 0xf1, 0x3c, 0x8a, 0xf0, 0x3c, 0x8a, 0xf1, 0x3c, 0x89, 0xf0, 0x3d, 0x8a, 0xf1,
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0x3d, 0x89, 0xf0, 0x3d, 0x89, 0xf0, 0x3d, 0x89, 0xf0, 0x3e, 0x89, 0xf0, 0x3d, 0x89, 0xf0,
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0x4a, 0x81, 0xed, 0x49, 0x81, 0xed, 0x4a, 0x81, 0xed, 0x49, 0x81, 0xed, 0x49, 0x81, 0xed,
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0x71, 0x8c, 0xe5, 0x3e, 0x4c, 0xcc, 0x3d, 0x4c, 0xcb, 0x65, 0x85, 0xe1, 0x3d, 0x89, 0xf0,
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0x3d, 0x89, 0xf0, 0x3d, 0x88, 0xf0, 0x3d, 0x89, 0xf0, 0x3d, 0x88, 0xf0, 0x3e, 0x88, 0xf0,
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0x3e, 0x88, 0xf0, 0x3e, 0x88, 0xf0, 0x3e, 0x88, 0xf0, 0x3f, 0x88, 0xf0, 0x3e, 0x88, 0xef,
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};
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static uint16_t rgb24hist[3 * 64];
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static uint8_t rgb24avg[3];
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int main(void)
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{
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LOG_INF("Input image preview:");
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pixel_print_rgb24frame_truecolor(image_rgb24, sizeof(image_rgb24), 20, 4);
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LOG_INF("RGB histogram of the image");
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pixel_rgb24frame_to_rgb24hist(image_rgb24, sizeof(image_rgb24),
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rgb24hist, ARRAY_SIZE(rgb24hist), NVAL);
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pixel_print_rgb24hist(rgb24hist, ARRAY_SIZE(rgb24hist), 16);
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LOG_INF("RGB channel averages of the image");
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pixel_rgb24frame_to_rgb24avg(image_rgb24, sizeof(image_rgb24), rgb24avg, NVAL);
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LOG_INF("- R: 0x%02x/0xff", rgb24avg[0]);
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LOG_INF("- G: 0x%02x/0xff", rgb24avg[1]);
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LOG_INF("- B: 0x%02x/0xff", rgb24avg[2]);
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return 0;
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}

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