How to multiply/upscale color depth?

[MitchelAlbertz]

I'm struggling with multiplying pixel values.
I've read through the examples and docs, but I can't figure out what the effective method is.
To be more precise, I'm attempting to achieve the following;

I have raw binary data that stores 3bit pixel values per byte (so values ranging from 0..7).
After I've read in the data, I want to 'upscale' this image, so the image is more clear (not a smudge of barely grey pixels).
Currently the image contrast if quite vague because most programs just use/default to 8bit depth:

In other words I want to change the Depth from 3 to 8, and thereby increase the perceived contrast.
So for example a value of '5' -> '160', '6' -> '192', 7 -> '224' (factor 32).

I've tried simply altering the Depth to another value, but it does not scale the values already present.
Also I've tried to do a Multiply operator (as documented here: https://usage.imagemagick.org/compose/#multiply).
But for some reason all outputs are pulled down to 1.

Here is the code sample:

// This is just test data
var data = new byte[16] { 7, 0, 7, 0, // First row is alternating max 3 bit value <-> 0
                                7, 7, 7, 7, // Second row is all pixels at max 3 bit value
                                1, 3, 5, 7, // Third row is incrementing values
                                0, 0, 0, 0 }; // Fourth row is empty values

using var image = new MagickImage();

image.ReadPixels(
    data: data,
    settings: new PixelReadSettings(
        width: 4,
        height: 4,
        storageType: StorageType.Char, // Char = byte
        "R") // Red/Cyan/Gray = first channel
    );

var pc = image.GetPixels();
foreach (var pixel in pc)
{
    var pixelValue = pixel.GetChannel(0);
    Console.WriteLine($"Pixel Raw of X{pixel.X} Y{pixel.Y} has value {pixelValue}");
}

// Red channel = gray scale channel (index 0). I don't know how else to create a 'pure' gray scale image.
var basePixelValue = MagickColor.FromRgb(32, 0, 0);
using var multiplyImage = new MagickImage(
    width: 4,
    height: 4,
    color: basePixelValue
);
// This doesn't seem to work...
image.Composite(multiplyImage, CompositeOperator.Multiply);

var pc2 = image.GetPixels();
foreach (var pixel in pc2)
{
    var pixelValue = pixel.GetChannel(0);
    Console.WriteLine($"Pixel after Multiply of X{pixel.X} Y{pixel.Y} has value {pixelValue}");
}

File.WriteAllBytes("c:\\temp\\images\\test_image.tiff", image.ToByteArray(MagickFormat.Tiff));

The console output is:

Pixel Raw of X0 Y0 has value 7
Pixel Raw of X1 Y0 has value 0
Pixel Raw of X2 Y0 has value 7
Pixel Raw of X3 Y0 has value 0
Pixel Raw of X0 Y1 has value 7
Pixel Raw of X1 Y1 has value 7
Pixel Raw of X2 Y1 has value 7
Pixel Raw of X3 Y1 has value 7
Pixel Raw of X0 Y2 has value 1
Pixel Raw of X1 Y2 has value 3
Pixel Raw of X2 Y2 has value 5
Pixel Raw of X3 Y2 has value 7
Pixel Raw of X0 Y3 has value 0
Pixel Raw of X1 Y3 has value 0
Pixel Raw of X2 Y3 has value 0
Pixel Raw of X3 Y3 has value 0
Pixel after Multiply of X0 Y0 has value 1
Pixel after Multiply of X1 Y0 has value 0
Pixel after Multiply of X2 Y0 has value 1
Pixel after Multiply of X3 Y0 has value 0
Pixel after Multiply of X0 Y1 has value 1
Pixel after Multiply of X1 Y1 has value 1
Pixel after Multiply of X2 Y1 has value 1
Pixel after Multiply of X3 Y1 has value 1
Pixel after Multiply of X0 Y2 has value 0
Pixel after Multiply of X1 Y2 has value 0
Pixel after Multiply of X2 Y2 has value 1
Pixel after Multiply of X3 Y2 has value 1
Pixel after Multiply of X0 Y3 has value 0
Pixel after Multiply of X1 Y3 has value 0
Pixel after Multiply of X2 Y3 has value 0
Pixel after Multiply of X3 Y3 has value 0

I'm using Magick.NET-Q8-AnyCPU Version=14.2.0.

Can someone help me out?

[dlemstra]

You could use the Fx method of MagickImage for this. You can multiply the red channel like this image.Fx("r*32");

p.s. The result of GetPixels is IDisposable so you should add a using: using var pc = image.GetPixels();