Bitmap Image as a dictionary key

问题

I want to know what size should be the image to use it as a hashset/dictionary key. I'm also thinking about using hash functions for this purpose but i'm afraid of hash collisions. I need to store about million of images.

回答1:

A bitmap image as a key? That's not a very good idea. Hashset keys should be as small as possible, otherwise performance will suffer significantly.

What you can do is calculate a hash value (say a SHA1) from the image, and then use that as the key. It's only 20 bytes so that should be a good size, much better than a full bitmap image anyway.

回答2:

It doesn't matter what data you use for key in a HashSet or Dictionary, but you need to implement a GetHashCode and an Equals method for it.

Hash collisions is not a problem. That will just put the two images in the same bucket, and use the Equals method to find the right image.

回答3:

Given your Image's bytes, you can use an algorithm such as MD5 or SHA1 to calculate a hash for it.

Example with bytes being your picture's byte array:

using (var md5 = new System.Security.Cryptography.MD5CryptoServiceProvider())
{
    var hash = Convert.ToBase64String(md5.ComputeHash(bytes));
    //Store hash
}

来源：https://stackoverflow.com/questions/13915954/bitmap-image-as-a-dictionary-key