The way it works is, in sequence:
- a person opens a page on your site, and that page happens to contain a piece of Revive Adserver invocation code.
- for the sake of simplicity, let's assume for now there is only a single invocation code on the page.
- that execution sends a request to the Revive Adserver installation, and it is counted as "an ad request".
- the ad server processes the request and selects a banner.
- as a response to the ad request, it sends back a block of HTML code presenting that banner to the browser.
- the browser "renders" the HTML code, which means that the banner gets displayed in the browser.
- what also happened is that the ad server attached a small, invisible, 1x1 transparent pixel to the HTML code it returned to the browser. This is the "logging pixel".
- the logging pixel is technically a small image, and the fact that the browser also renders that, means a call goes to the ad server to say: "count an ad impression".
The process above also occurs if the invocation code happens to be outside of the visible part of the page, so outside the "viewport". An impression is not the same as a viewable impression. Revive Adserver does not measure viewability.