Grayscale Converter is a tool for artists who work with grayscales. It can help to visually translate between different grayscales, and plan (and calculate) value compression from one scale to another. For artists working with traditional media, Grayscale Converter is best used alongside an actual physical grayscale such as the Munsell Neutral Value Scale from X-Rite; for artists working digitally, it can be a standalone translator alongside products like Adobe® Photoshop® or Corel® Painter™.

figure 1

Figure 1 shows a grayscale drawn on tinted paper in black and white charcoal on the left, with superimposed arrows (colored for clarity) showing the correspondence between the drawn grayscale and the actual physical grayscale reference on the right. Note that the physical grayscale has a full range of values, where the range of values reachable in charcoal is more limited. The black and white swatches were drawn first, then identified on the physical grayscale. Grayscale Converter calculated the corresponding intervals for the intermediate steps, to be used as a guide in drawing with these materials.

A full explanation follows below.

How to use Grayscale Converter

The main screen of Grayscale Converter shows two grayscales on the left and right sides of the screen, which may be the same or different, and a table in the middle showing the steps of the left scale translated into corresponding values on the right scale. The table can be scrolled with a touch if it is bigger than the screen's display.

Additionally, each scale has two "compression handles" that can be used to independently restrict the range for each scale. The default position for these handles is at the top and bottom of each scale, but they can be moved by dragging. This makes it possible, for instance, to compress a Munsell value scale from the full scale on the left (by leaving the handles in their default positions at the ends of the scale) to a range of, say, 2-8 on the right (by dragging the lower handle up to value 2 and the upper handle down to value 8). Grayscale Converter will calculate the steps' values on the fly as the handles are dragged.

Touch the "settings" button to load different grayscales, change the number of divisions (such as, every value step, every ½ or ¼ step, or to a manual setting if you want to be specific), and change the drag increments and value rounding controls.

Grayscale Converter ships with a number of commonly-used presets, such as a 0-to-10 scale (as used by the Munsell color system), a 1-to-9 scale, a 0-to-256 scale for digital artists, etc. You can also easily make your own to add to the list. Simply supply a name (and optional description), the numeric values for black and white, and the size of the steps to be used when drawing.

On the iPad, the controls can be used in a split-view model that dynamically updates the view as the settings are changed.

About value and value compression

Artists speaking of "value" are referring to the lightness or darkness of a color. Color has three attributes: hue (for example, blue or yellow), value (lightness to darkness), and chroma (intensity or saturation). Although all three are important to artists, value is the most important attribute for making an image believable; hues and chromas can be off and the image can still be understood, but if the values aren't correct, it can look chunky, blocky, or muddy. Artists who want their images to read well must pay special attention to values.

"Value compression" generally refers to the fact that the value range of art materials like paint, charcoal or pastels does not reach the full range of values found in nature. The darkest black paint available is not as dark as the darkest part of a shadow in indoor lighting, for example, nor can the whitest paint (or paper) capture the effect of sunlight on that same paper. An artist painting a still life and trying to match the values she sees as closely as possible will often find that she "runs out of room" on the light and dark ends of the scale, unless she has compressed the entire range in an even manner.

figure 2

Figure 2 shows an image of a sphere next to a charcoal drawing of that sphere. Notice that the value range of the sphere is wider than the value range of the drawing: the shadows are darker and the highlights are lighter than it was possible to reach with the black and white charcoal used for the drawing. Value compression is necessary to "squeeze" the range of values used in the drawing down in proportion with the available range of charcoal - in this case, approximately Munsell values 2.5 to 8. The full range of the actual sphere was approximately range 1.5 to 8.5. Grayscale Converter calculated the intervals for the steps, which was used as a guide for how to create the proper compression in the drawing.

The steps involved in this process were:

  1. Select the Munsell scale on both the left and right grayscales (since the Munsell scale is the one we're using in this case)
  2. Set the left subdivisions to "Every ½ step", so we'll get half-value intervals on the full scale
  3. (Optional) Set the right handle snap-to range to "Every ½ step" for convenience
  4. Drag the compression handles on the right scale to 8 on top, and 2.5 at the bottom.

figure 3

Grayscale Converter renders the compression and shows the values for the steps (figure 3). For example, value 8 on the real object would be rendered as value 6.9 in the drawing, and so forth.

Technical notes

In the present version of Grayscale Converter, the grayscale shown on the screen is a visual reference only; the actual values will be determined by the scale. All calculations are linear and presume an equal lightness progression between value steps.

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