Lines appear transparent when below a certain thickness

[prem_parallax]

Lines lose opacity as their pixel width is reduced and its ruining my workflow! I'm working on a 1920 x 1080 wide canvas with 300 dpi, so I know it's not my resolution. Please help!

[ExUSA]

If you zoom into 100% (or 200% on a high-dpi display) you'll see things clearly. When zoomed out, your monitor can't show thin lines and small details clearly.

[prem_parallax]

It's not just the display, I exported my artwork and the lines did not change. 

[davescm · Accepted solution]

Photoshop, like any other raster image editor, works in pixels. So a pixel is the minimum unit available in your image. There are no half pixels in a raster image, only whole pixels. If you select a line width of 0.5 pixels then the only way to display that using whole pixels is to reduce the value in that pixel, or make it transparent, which is what you are seeing.

Dave