Hi,
There are at least three approaches of volume analysis:
a) Time-based volume --- cumulative volume within a fixed period of time
b) Volume profile --- volume by price
c) Volume by wave ---
As regards your chart example, there is no such thing as "up volume" or "down volume"; there is only volume. If one is using color-coding, the color depends on the relationship between a given bar and the previous bar. But volume, like price, is continuous, so a given bar represents only the number of trades for that interval. Whether the volume is on the demand side or the supply side will be reflected in the behavior of price.
Therefore, a "long" bar is due to a greater than average number of trades. If price goes up, demand had the upper hand. Color is irrelevant.
Yes, volume is just a volume. When we have volume = 100 it just mean that somebody bought 100 shares and somebody sold to him these 100 shares. just from volume we cannot state that there are more buyers or more sellers. However, together with price movement we can get some points. Volume during price move means that buyers are more greedy than sellers as they are ready to buy at higher price. Opposite is true for volume to the price down side. To do volume analysis you have to differentiate volume to the price up-side from volume to price down-side. Up-volume, bullish volume, positive volume is just a name. The question is what do you see behind it and how you interpret it.
By the way,