What does a screenshot REALLY capture?

[Shadoninja]

I woke up this morning to a very strange blurry/artifact-looking display on one of my three PC monitors. I have 3 monitors hooked up and only one of them had this extremely odd look to it. I used my sceenshot utility to document the strange display before trying to fix anything. I changed the resolution on the monitor in question to something else and then cycled it back to the original resolution and it was fixed. But the screenshot I took was also fixed... doh. So here is my question: what does a screenshot capture? Does it capture what your graphics card is seeing? Does it capture what the OS *thinks* you are seeing? (I am using Windows). Bonus question: Ideas for what can cause one monitor in a multi-monitor display to look completely broken until a resolution cycle is done?

[Guest]

A screenshot utility captures the framebuffer of your GPU.(Framebuffer stores pixels to be drawn to the displays) This is where the pixels are stored, and is what get's drawn to your screen(s). Your screenshot was probably normal(where your screen wasn't) because there was an connection issue or a display controller crashed. There are controllers in your GPU which drive the port's(and the connected display). If one of those controllers crashed, your display would look weird/artifacted, but the framebuffer would still be fine, thus your screenshot would look normal.

[Mira Yurizaki]

It copies whatever's in the frame buffer that the display is copying from at the time you hit the key.

[minibois]

It will capture what Windows sees.

This is why for example using the screenshot button doesn't work inside full screen videogames (or maybe it does nowadays, at least it didn't use to); a full screen videogame is something that Windows passes from your GPU directly to your screen as to not interfere with it. 

 

Another reason I say "Windows takes the screenshot" is because they can change the picture. For example, I once saw some funny thing on a show I was watching on Netflix (desktop app) and wanted to screenshot this. When pasting the screenshot in Paint to crop it, I noticed it made the video on Netflix black. Only the video, the subtitles were still present.

 

Also, the resolution cycle thing.. I would have to assume it was an error with your GPU of some sorts, you changed the res (which makes the GPU have to render the screen again) and maybe now it didn't have the error? I'm just guessing, but that could be it..

[Kodiak.]

Screenshots capture the framebuffer that is being sent from your GPU to your monitor; in most cases this is what you're seeing. The only thing I could think of is that if a controller on the card failed, meaning the display would be full of artifacts but the framebuffer would be fine.