{"id":790,"date":"2020-12-08T11:05:00","date_gmt":"2020-12-08T03:05:00","guid":{"rendered":"http:\/\/39.96.58.60\/?p=790"},"modified":"2022-10-18T16:37:12","modified_gmt":"2022-10-18T08:37:12","slug":"focal-loss%e6%8d%9f%e5%a4%b1%e5%87%bd%e6%95%b0pytorch%e5%ae%9e%e7%8e%b0","status":"publish","type":"post","link":"http:\/\/www.yatenglg.cn\/blog\/?p=790","title":{"rendered":"Focal loss\u635f\u5931\u51fd\u6570pytorch\u5b9e\u73b0"},"content":{"rendered":"\n<p>focal loss \u635f\u5931\u51fd\u6570\u57fa\u4e8e\u4ea4\u53c9\u71b5\u635f\u5931\u51fd\u6570,\u5728\u4ea4\u53c9\u71b5\u7684\u57fa\u7840\u4e0a,\u5f15\u5165\u4e86\u03b1\u4e0e\u03b3\u4e24\u4e2a\u4e0d\u540c\u7684\u8c03\u6574\u56e0\u5b50.<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>1. \u4ea4\u53c9\u71b5\u635f\u5931<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img width=\"560\" height=\"284\" src=\"http:\/\/39.96.58.60\/wp-content\/uploads\/2020\/12\/crossempty.jpeg\" alt=\"\" class=\"wp-image-792\" srcset=\"http:\/\/www.yatenglg.cn\/blog\/wp-content\/uploads\/2020\/12\/crossempty.jpeg 560w, http:\/\/www.yatenglg.cn\/blog\/wp-content\/uploads\/2020\/12\/crossempty-300x152.jpeg 300w\" sizes=\"(max-width: 560px) 100vw, 560px\" \/><\/figure>\n\n\n\n<p class=\"has-medium-font-size\"><strong>2. \u5e26\u5e73\u8861\u56e0\u5b50\u7684\u4ea4\u53c9\u71b5\u635f\u5931<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img width=\"557\" height=\"290\" src=\"http:\/\/39.96.58.60\/wp-content\/uploads\/2020\/12\/weightcorssempty.jpeg\" alt=\"\" class=\"wp-image-793\" srcset=\"http:\/\/www.yatenglg.cn\/blog\/wp-content\/uploads\/2020\/12\/weightcorssempty.jpeg 557w, http:\/\/www.yatenglg.cn\/blog\/wp-content\/uploads\/2020\/12\/weightcorssempty-300x156.jpeg 300w\" sizes=\"(max-width: 557px) 100vw, 557px\" \/><\/figure>\n\n\n\n<p class=\"has-medium-font-size\"><strong>3. focal loss\u635f\u5931\u51fd\u6570<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img width=\"550\" height=\"143\" src=\"http:\/\/39.96.58.60\/wp-content\/uploads\/2020\/12\/focalloss.jpeg\" alt=\"\" class=\"wp-image-794\" srcset=\"http:\/\/www.yatenglg.cn\/blog\/wp-content\/uploads\/2020\/12\/focalloss.jpeg 550w, http:\/\/www.yatenglg.cn\/blog\/wp-content\/uploads\/2020\/12\/focalloss-300x78.jpeg 300w\" sizes=\"(max-width: 550px) 100vw, 550px\" \/><\/figure>\n\n\n\n<p class=\"has-medium-font-size\"><strong>4. \u5e26\u5e73\u8861\u56e0\u5b50\u7684focal loss\u635f\u5931\u51fd\u6570<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img width=\"560\" height=\"228\" src=\"http:\/\/39.96.58.60\/wp-content\/uploads\/2020\/12\/weightfocalloss.jpeg\" alt=\"\" class=\"wp-image-795\" srcset=\"http:\/\/www.yatenglg.cn\/blog\/wp-content\/uploads\/2020\/12\/weightfocalloss.jpeg 560w, http:\/\/www.yatenglg.cn\/blog\/wp-content\/uploads\/2020\/12\/weightfocalloss-300x122.jpeg 300w\" sizes=\"(max-width: 560px) 100vw, 560px\" \/><\/figure>\n\n\n\n<div class=\"hcb_wrap\"><pre class=\"prism undefined-numbers lang-python\" data-lang=\"Python\"><code># -*- coding: utf-8 -*-\n# @Author  : LG\nfrom torch import nn\nimport torch\nfrom torch.nn import functional as F\n \nclass focal_loss(nn.Module):    \n    def __init__(self, alpha=0.25, gamma=2, num_classes = 3, size_average=True):\n        &quot;&quot;&quot;\n        focal_loss\u635f\u5931\u51fd\u6570, -\u03b1(1-yi)**\u03b3 *ce_loss(xi,yi)      \n        \u6b65\u9aa4\u8be6\u7ec6\u7684\u5b9e\u73b0\u4e86 focal_loss\u635f\u5931\u51fd\u6570.\n        :param alpha:   \u963f\u5c14\u6cd5\u03b1,\u7c7b\u522b\u6743\u91cd.      \u5f53\u03b1\u662f\u5217\u8868\u65f6,\u4e3a\u5404\u7c7b\u522b\u6743\u91cd,\u5f53\u03b1\u4e3a\u5e38\u6570\u65f6,\u7c7b\u522b\u6743\u91cd\u4e3a[\u03b1, 1-\u03b1, 1-\u03b1, ....],\u5e38\u7528\u4e8e \u76ee\u6807\u68c0\u6d4b\u7b97\u6cd5\u4e2d\u6291\u5236\u80cc\u666f\u7c7b , retainnet\u4e2d\u8bbe\u7f6e\u4e3a0.25\n        :param gamma:   \u4f3d\u9a6c\u03b3,\u96be\u6613\u6837\u672c\u8c03\u8282\u53c2\u6570. retainnet\u4e2d\u8bbe\u7f6e\u4e3a2\n        :param num_classes:     \u7c7b\u522b\u6570\u91cf\n        :param size_average:    \u635f\u5931\u8ba1\u7b97\u65b9\u5f0f,\u9ed8\u8ba4\u53d6\u5747\u503c\n        &quot;&quot;&quot;\n        \n        super(focal_loss,self).__init__()\n        self.size_average = size_average\n        if isinstance(alpha,list):\n            assert len(alpha)==num_classes   # \u03b1\u53ef\u4ee5\u4ee5list\u65b9\u5f0f\u8f93\u5165,size:[num_classes] \u7528\u4e8e\u5bf9\u4e0d\u540c\u7c7b\u522b\u7cbe\u7ec6\u5730\u8d4b\u4e88\u6743\u91cd\n            print(&quot;Focal_loss alpha = {}, \u5c06\u5bf9\u6bcf\u4e00\u7c7b\u6743\u91cd\u8fdb\u884c\u7cbe\u7ec6\u5316\u8d4b\u503c&quot;.format(alpha))\n            self.alpha = torch.Tensor(alpha)\n        else:\n            assert alpha&lt;1   #\u5982\u679c\u03b1\u4e3a\u4e00\u4e2a\u5e38\u6570,\u5219\u964d\u4f4e\u7b2c\u4e00\u7c7b\u7684\u5f71\u54cd,\u5728\u76ee\u6807\u68c0\u6d4b\u4e2d\u4e3a\u7b2c\u4e00\u7c7b\n            print(&quot; --- Focal_loss alpha = {} ,\u5c06\u5bf9\u80cc\u666f\u7c7b\u8fdb\u884c\u8870\u51cf,\u8bf7\u5728\u76ee\u6807\u68c0\u6d4b\u4efb\u52a1\u4e2d\u4f7f\u7528 --- &quot;.format(alpha))\n            self.alpha = torch.zeros(num_classes)\n            self.alpha[0] += alpha\n            self.alpha[1:] += (1-alpha) # \u03b1 \u6700\u7ec8\u4e3a [ \u03b1, 1-\u03b1, 1-\u03b1, 1-\u03b1, 1-\u03b1, ...] size:[num_classes]\n        self.gamma = gamma\n        \n    def forward(self, preds, labels):\n        &quot;&quot;&quot;\n        focal_loss\u635f\u5931\u8ba1\u7b97        \n        :param preds:   \u9884\u6d4b\u7c7b\u522b. size:[B,N,C] or [B,C]    \u5206\u522b\u5bf9\u5e94\u4e0e\u68c0\u6d4b\u4e0e\u5206\u7c7b\u4efb\u52a1, B \u6279\u6b21, N\u68c0\u6d4b\u6846\u6570, C\u7c7b\u522b\u6570        \n        :param labels:  \u5b9e\u9645\u7c7b\u522b. size:[B,N] or [B]        \n        :return:\n        &quot;&quot;&quot;        \n        # assert preds.dim()==2 and labels.dim()==1        \n        preds = preds.view(-1,preds.size(-1))        \n        self.alpha = self.alpha.to(preds.device)        \n        preds_softmax = F.softmax(preds, dim=1) # \u8fd9\u91cc\u5e76\u6ca1\u6709\u76f4\u63a5\u4f7f\u7528log_softmax, \u56e0\u4e3a\u540e\u9762\u4f1a\u7528\u5230softmax\u7684\u7ed3\u679c(\u5f53\u7136\u4f60\u4e5f\u53ef\u4ee5\u4f7f\u7528log_softmax,\u7136\u540e\u8fdb\u884cexp\u64cd\u4f5c)        \n        preds_logsoft = torch.log(preds_softmax)\n        preds_softmax = preds_softmax.gather(1,labels.view(-1,1))   # \u8fd9\u90e8\u5206\u5b9e\u73b0nll_loss ( crossempty = log_softmax + nll )        \n        preds_logsoft = preds_logsoft.gather(1,labels.view(-1,1))        \n        self.alpha = self.alpha.gather(0,labels.view(-1))        \n        loss = -torch.mul(torch.pow((1-preds_softmax), self.gamma), preds_logsoft)  # torch.pow((1-preds_softmax), self.gamma) \u4e3afocal loss\u4e2d (1-pt)**\u03b3\n        loss = torch.mul(self.alpha, loss.t())        \n        if self.size_average:        \n            loss = loss.mean()        \n        else:            \n            loss = loss.sum()        \n        return loss<\/code><\/pre><\/div>\n\n\n\n<p>\u8be6\u7ec6\u7684\u4f7f\u7528\u4f8b\u5b50\u8bf7\u5230<a href=\"https:\/\/github.com\/yatengLG\/Focal-Loss-Pytorch\/blob\/master\/Demo.ipynb\">Github<\/a>\u67e5\u770bjupyter-notebook.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>focal loss \u635f\u5931\u51fd\u6570\u57fa\u4e8e\u4ea4\u53c9\u71b5\u635f\u5931\u51fd\u6570,\u5728\u4ea4\u53c9\u71b5\u7684\u57fa\u7840\u4e0a,\u5f15\u5165\u4e86\u03b1\u4e0e\u03b3\u4e24\u4e2a\u4e0d\u540c\u7684\u8c03\u6574\u56e0\u5b50. 1. \u4ea4&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[8,5],"tags":[],"_links":{"self":[{"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=\/wp\/v2\/posts\/790"}],"collection":[{"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=790"}],"version-history":[{"count":4,"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=\/wp\/v2\/posts\/790\/revisions"}],"predecessor-version":[{"id":798,"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=\/wp\/v2\/posts\/790\/revisions\/798"}],"wp:attachment":[{"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=790"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=790"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.yatenglg.cn\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=790"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}