Do values do all the work?

It's a misleading question. Does the framing and foundation of your house give it shape and structure? Yes, but the design, style and look of the house overlays the structure, and people see only what is on the surface.

A painting with an incorrect or wonky value structure will be awkward. The light will look wrong. Forms won't turn in the space properly.  It will lack atmosphere or depth.  This is true no matter if you paint directly or indirectly, or some combination of the two.

I can tell you from experience that even though I've been using Munsell to mix my paints for 16 years, and I mix values correctly through daily practice, laying paint down means that those correct values will be impacted by the surface they go down on. 

It's not enough to mix and paint an area once and expect the value of the dry paint to math what you mixed. 

It will not. 

If you work on a white surface your initial layers of paint will be higher in chroma than what you mixed, by about 2 chroma steps. 

If you work on a middle value toned canvas your initial color will be lower in value and chroma. Etc.

The only solution I've found to this is to have the ability to restate my values. That's why, if you follow me on social media, you'll see me do several underpainting sessions just to get the values correct. Paint does strange things and as painters we need to know how to make it do what we want. 

• Values give shape and form to your subjects. 

• Atmosphere, the sense that the space is not flat or empty, comes from superb control of values. 

• The more compressed the value range of your painting the more important your command of values becomes.  

• A painting with compressed values, as in alla prima, can be quite beautiful if the values are compressed correctly.    

• A full value range will give your work an unquestioned sense of reality. 

Values are the underpinning of every painting, no matter what the style. 

Humans can see just over 1,000 subtle value shifts. No matter how much light is present we cannot see more than this many values. We see more subtlety in a dark space than in full light.

It's a survival advantage. Our ancestors didn't need to see subtle shifts in good light, but in a dark cave it was good to be able to see that the stick you were reaching for was actually a snake. 

As artists we probably don't spend that much time in caves but our brain still functions as if we do. This is why it's critical to see the large structure and forms before focusing on the smaller.

One of the tempting things about using photo reference is being able to zoom in on an area. It's a great advantage if you have a reliable guide to the values you're actually seeing. But that quirk of the brain I described above is busy tricking you while you're zoomed in. It's throwing off your ability to judge just how dark or light forms are. 

If you want to be able to translate photos into accurate value maps this tutorial will give you that skill. You'll need Photoshop or Affinity Photo. Other programs might work but I can't speak to them.