add command line options and temperature calibration

without temperature calibration 0.3%
with ~5%

model name	: Intel(R) Core(TM) i7-3615QM CPU @ 2.30GHz

examples/live.rs

@@ -1,9 +1,31 @@
+use clap::Parser;
 use dotenv::dotenv;
 use std::io::Write;
 use thermaldecoder::{Header, HDR_SIZE};
 use v4l::video::Output;
 
+#[derive(Parser, Debug)]
+#[command(version, about, long_about = None)]
+struct Args {
+    #[arg(short, long, default_value_t = false)]
+    temperature: bool,
+    #[arg(short, long, default_value = "/dev/video0")]
+    device: String,
+}
+
+fn pixel_to_celcius(x: u16) -> u16 {
+    let x: f64 = x.into();
+    let x = x / 256.0;
+    let t = (-1.665884e-08) * x.powf(4.)
+        + (1.347094e-05) * x.powf(3.)
+        + (-4.396264e-03) * x.powf(2.)
+        + (9.506939e-01) * x
+        + (-6.353247e+01);
+    (t * 256.0) as u16
+}
+
 fn main() -> anyhow::Result<()> {
+    let args = Args::parse();
     dotenv().ok();
     let device = match std::env::var("THERMALCAM_IFACE=enp1s0f0") {
         Ok(d) => {
@@ -21,9 +43,7 @@ fn main() -> anyhow::Result<()> {
     // get the default Device
 
     println!("Using device {}", device.name);
-    let output = std::env::args()
-        .nth(1)
-        .expect("required output file argument");
+    let output = args.device;
     println!("Using output v4l2loopback device {}", output);
 
     const WIDTH: usize = 288;
@@ -73,8 +93,12 @@ fn main() -> anyhow::Result<()> {
                 // possibly limitation of current v4l2loopback or v4l rust wrapper or libv4l2
                 let mut swapped = [0u8; FRAME_LEN];
                 for i in 0..FRAME_LEN / 2 {
-                    swapped[i * 2] = frame[i * 2 + 1];
-                    swapped[i * 2 + 1] = frame[i * 2];
+                    let mut pixel = u16::from_be_bytes([frame[i * 2], frame[i * 2 + 1]]);
+                    if args.temperature {
+                        pixel = pixel_to_celcius(pixel);
+                    }
+                    let pixel_swapped = pixel.to_le_bytes();
+                    swapped[i * 2..i * 2 + 2].copy_from_slice(&pixel_swapped);
                 }
                 out.write_all(&swapped[..])?;
             }