How will we know if the correction has ended or not ?
Well, first of all, there's not really such a thing as "THE" correction. Each chart range has its own definition of a correction. So for example, as you already observed, the shorter range charts have completed their "correction" and are in the green. But their cycles are so short that they don't really count for most people. You're probably thinking of a timescale in terms of a few days (e.g. the last big rise lasted a few days and the subsequent correction has lasted a couple of days). So the chart that corresponds to that sort of timescale would be the 4-hour or the 6-hour.
Secondly, every trader has their preferred indicators that they give different priorities to depending on what type of stock they're trading, the nature of the market, timescales, volatility etc.
In the bitcoin market, I tend to use momentum indicators at short ranges and volume at long ranges (for example On Balance Volume which I find is useless on a day to day basis but very informative on a month to month basis).
So in conclusion my own definition of "when the current correction has ended" (which is purely subjective - other people will have other definitions) is when the 4-Hour MACD indicator shows that selling momentum is exhausted at that particular chart range.
Thats when this little indicator's red bars get shorter and start turning green again...
So you see how the blue and brown lines are still quite parallel ? That shows that the market is still being driven down at that chart range (it's being driven up at lower order ranges - shorter timescales). However, the histogram shows that the lines are starting to converge which means the rate of selling is slowing, even though it's still being driven down. When the blue line crosses the brown, the buy and sell momentum have reached equilibrium and many traders pick a chart range to trade and go long at that point.
It's not bullet proof though. It's just one indicator. Sometimes you get a double dip right at the crossover point and you get a huge cash-out instead. That can happen if trading sentiment reverses and shorters use the crossover point to anticipate maximum liquidity into which to dump. Right now, with halving coming up and stuff, I don't really see that happening but you know what these markets are like, anything can happen