Copied from: https://bitbucket.org/Unity-Technologies/2ddemos

PerfectPixel.cs

using System;
using System.Linq;
using UnityEngine;
using System.Collections;
using System.Collections.Generic;

[System.Serializable]
public class PerfectOverride
{
    public int referenceOrthographicSize;
    public float referencePixelsPerUnit;
}

public class PerfectPixel : MonoBehaviour
{
    public int referenceOrthographicSize;
    public float referencePixelsPerUnit;
    public List<PerfectOverride> overrides;

    private int lastSize = 0;

    // Use this for initialization
    void Start()
    {
        UpdateOrthoSize();
    }

    PerfectOverride FindOverride(int size)
    {
        return overrides.FirstOrDefault(x => x.referenceOrthographicSize == size);
    }

    void UpdateOrthoSize()
    {
        lastSize = Screen.height;

        // first find the reference orthoSize
        float refOrthoSize = (referenceOrthographicSize / referencePixelsPerUnit) * 0.5f;

        // then find the current orthoSize
        var overRide = FindOverride(lastSize);
        float ppu = overRide != null ? overRide.referencePixelsPerUnit : referencePixelsPerUnit;
        float orthoSize = (lastSize / ppu) * 0.5f;

        // the multiplier is to make sure the orthoSize is as close to the reference as possible
        float multiplier = Mathf.Max(1, Mathf.Round(orthoSize / refOrthoSize));

        // then we rescale the orthoSize by the multipler
        orthoSize /= multiplier;

        // set it
        this.GetComponent<Camera>().orthographicSize = orthoSize;

        Debug.Log(lastSize + " " + orthoSize + " " + multiplier + " " + ppu);
    }

    // Update is called once per frame
    void Update()
    {
#if UNITY_EDITOR
        if (lastSize != Screen.height)
            UpdateOrthoSize();
#endif
    }
}