Take a screenshot into a png file

ScreenshotManager

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.SceneManagement;
using System.IO;

/// <summary>
/// https://answers.unity.com/questions/12070/capture-rendered-scene-to-png-with-background-tran.html
/// </summary>

public class ScreenshotManager : MonoBehaviour
{
    /// <summary>
    /// if multiple camera to render
    /// must list each camera in order back->front
    /// if empty : will use Camera.main
    /// </summary>
    public string[] layersCameraNames;

    Camera[] layers; // stack of cameras
    Texture2D virtualPhoto; // Tex2D that will be saved into png
    
    /// <summary>
    /// for debug, 1 render per camera
    /// </summary>
    public RenderTexture[] layersTexs;

    IEnumerator Start()
    {
        setup();

        yield return null;

        takePhoto();

        //yield return new WaitForSeconds(3f);
        yield return null;

        unSetup();
    }

    [ContextMenu("start process")]
    public void setup()
    {
        if (layersCameraNames == null)
            layersCameraNames = new string[0];

        // get all cameras to render
        if(layersCameraNames.Length > 0)
        {
            layers = getCameras(layersCameraNames);
        }
        else
        {
            //layers = getCameras(new string[] { Camera.main.name });
            layers = new Camera[] { Camera.main };
        }
    }

    Camera[] getCameras(string[] names)
    {
        Camera[] cams = GameObject.FindObjectsOfType<Camera>();
        List<Camera> output = new List<Camera>();
        for (int i = 0; i < cams.Length; i++)
        {
            for (int j = 0; j < names.Length; j++)
            {
                if (cams[i].name.EndsWith(names[j]))
                {
                    output.Add(cams[i]);
                }
            }
        }
        return output.ToArray();
    }

    public void takePhoto()
    {
        // capture the virtuCam and save it as a square PNG.


        // https://gamedev.stackexchange.com/questions/184785/saving-png-from-render-texture-results-in-much-darker-image=
        // can't use external render tex

        // https://docs.unity3d.com/ScriptReference/RenderTexture.html

        RenderTexture mRt = new RenderTexture(Screen.width, Screen.height, 32);

        // the 24 can be 0,16,24, formats like
        // RenderTextureFormat.Default, ARGB32 etc.

        // camera render : https://docs.unity3d.com/ScriptReference/Camera.Render.html

        RenderTexture.active = mRt;

        for (int i = 0; i < layers.Length; i++)
        {
            // debug, to save each pass into specific given render textures
            if(layersTexs.Length > 0)
            {
                // debug, capture layer
                layers[i].targetTexture = layersTexs[i];
                layers[i].Render();
            }

            // inject into final tex
            layers[i].targetTexture = mRt;
            layers[i].Render();

            //Debug.Log("rendering " + layers[i], layers[i]);
        }

        Camera cam = layers[0];

        //generate tex
        int w = cam.targetTexture.width;
        int h = cam.targetTexture.height;

        //var texFormat = TextureFormat.RGBAFloat;
        var texFormat = TextureFormat.RGB48; // 16bits, no alpha

        virtualPhoto = new Texture2D(w, h, texFormat, 
            false); // false, meaning no need for mipmaps

        //extract info from render texture
        //https://docs.unity3d.com/ScriptReference/Texture2D.ReadPixels.html
        // "Reads pixels from the current render target and writes them to a texture."
        virtualPhoto.ReadPixels(new Rect(0, 0, w, h), 0, 0);
        virtualPhoto.Apply();

        RenderTexture.active = null; //can help avoid errors 
                                     //cam.targetTexture = null;
                                     // consider ... Destroy(tempRT);
                                     //clearPinkPixels();
        //DestroyImmediate(mRt);

        saveToPng();

    }

    /// <summary>
    /// remove all pink pixel to alpha transparent ones
    /// </summary>
    void clearPinkPixels()
    {
        Color32[] pixels = virtualPhoto.GetPixels32();
        int count = 0;
        for (int i = 0; i < pixels.Length; i++)
        {
            //pink pixel ?
            if (
              pixels[i].r > 0.99f &&
              pixels[i].g < 0.01f &&
              pixels[i].b > 0.99f)
            {
                count++;
                pixels[i].r = pixels[i].b = pixels[i].g = 0;
                pixels[i].a = 0;
            }
        }
        virtualPhoto.SetPixels32(pixels);
        virtualPhoto.Apply();

        Debug.Log("modified " + count + " pink pixels / out of " + pixels.Length + " pixels total");
    }

    void saveToPng()
    {

        byte[] bytes;
        //virtualPhoto.alphaIsTransparency = true;
        bytes = virtualPhoto.EncodeToPNG();

        string nm = Random.Range(10000, 99999).ToString();

        if(!Directory.Exists(ProjectStatics.dirShot))
        {
            Directory.CreateDirectory(ProjectStatics.dirShot);
        }

        string path = ProjectStatics.dirShot + "/capture_" + nm + ".png";

        UiFeedback.log("snapshot @ " + path);

        System.IO.File.WriteAllBytes(path, bytes);
        // virtualCam.SetActive(false); ... no great need for this.

        //DestroyImmediate(virtualPhoto);
    }

    /// <summary>
    /// entry point
    /// will load a scene with the scritpt
    /// script will auto launch, take pic, and unload
    /// </summary>
    static public AsyncOperation call()
    {
        return SceneManager.LoadSceneAsync(ProjectStatics.sceneExportName, LoadSceneMode.Additive);
    }

    //roll back whatever is needed
    protected void unSetup()
    {
        RenderTexture.active = null;

        for (int i = 0; i < layers.Length; i++)
        {
            layers[i].targetTexture = null;
        }
        layers = null;

        //remove scene after
        SceneManager.UnloadSceneAsync(ProjectStatics.sceneExportName);
    }

}

public class ProjectStatics
{
    public const string sceneExportName = "screenshoter";

    public static string dirRoot = string.Empty;
    public static string dirShot = "snapshots";
    //public static string dirGif = "output";

    public const string fileForm = "form.txt";

    static public int sessionId = -1;

    public const string ppref_uniq = "ppref_uniq_seed";

    static public void generateSessionId()
    {
        //get and inc seed
        int seed = PlayerPrefs.GetInt(ppref_uniq, 0);
        seed += 1;
        PlayerPrefs.SetInt(ppref_uniq, seed);

        sessionId = seed;
    }

    [RuntimeInitializeOnLoadMethod]
    static protected void generatePath()
    {
        //sessionId = PlayerPrefs.GetInt(ppref_uniq, 0);
        generateSessionId();


        //https://answers.unity.com/questions/1181652/difference-between-applicationpersistantdatapath-v.html
        // in editor : Assets (without last /)
        // in player : ?

        string appPath = Application.dataPath;
        Debug.Log(appPath);

        dirRoot = appPath.Substring(0, appPath.LastIndexOf('/')); // remove "Assets"

        dirShot = System.IO.Path.Combine(dirRoot, dirShot);
        //dirGif = System.IO.Path.Combine(Application.dataPath, dirGif);

        //Debug.Log("~ProjectStatics~ gif save dir path : " + dirGif);
        Debug.Log("~ProjectStatics~ shots save dir path : " + dirShot);
    }
}