User Guide

GNU Image Manipulation Program
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HSV
HSV is a color model which has components for Hue (the color, such as blue or red), Saturation (how strong the color is)
and Value (the brightness).
The RGB mode is very well suited to computer screens, but it doesn’t let us describe what we see in everyday life; a light
green, a pale pink, a dazzling red, etc. The HSV model takes these characteristics into account. HSV and RGB are not
completely independent of each other. You can see that with the Color Picker tool; when you change a color in one of the
color models, the other one also changes. Brave souls can read Grokking the GIMP, which explains their interrelationship.
• Hue: This is the color itself, which results from the combination of primary colors. All shades (except for the gray
levels) are represented in a chromatic circle: yellow, blue, and also purple, orange, etc. The chromatic circle (or ‘color
wheel’) values range between 0 and 360. (The term ‘color’ is often used instead of ‘Hue’. The RGB colors are ‘primary
colors’.)
• Saturation : This value describes how pale the color is. A completely unsaturated color is a shade of gray. As the
saturation increases, the color becomes a pastel shade. A completely saturated color is pure. Saturation values go from
0 to 100, from white to the purest color.
• Value : This value describes the luminosity, the luminous intensity. It is the amount of light emitted by a color. You can
see a change of luminosity when a colored object is moved from being in the shadow to being in the sun, or when you
increase the luminosity of your screen. Values go from 0 to 100. Pixel values in the three channels are also luminosities:
‘Value’ in the HSV color model is the maximum of these elementary values in the RGB space (scaled to 0-100).
I
Image Hose
An image hose in GIMP is a special type of brush which consists of several images. For example, you could have a brush
with footprints, which consists of two images, one for the left footprint and one for the right. While painting with this
brush, a left footprint would appear first, then a right footprint, then a left one, etc. This type of brush is very powerful.
An image hose is also sometimes called an ‘image pipe’ or ‘animated brush’. An image hose is indicated in the Brushes
dialog by a small red triangle in the lower right corner of the brush’s symbol.
For information concerning creating an image hose, please see the Using Animated Brushes and Using Brushes sections.
Incremental, paint mode
Incremental mode is a paint mode where each brush stroke is drawn directly on the active layer. When it is set, each
additional stroke of the brush increases the effect of the brush, up to the maximum opacity for the brush.
If incremental mode is not set, brush strokes are drawn on a canvas buffer, which is then combined with the active layer.
The maximum effect of a brush is then determined by the opacity, and stroking with the brush repeatedly does not increase
the effect beyond this limit.
The two images above were created using a brush with spacing set to 60 pixels. The image on the left shows non-
incremental painting and the image on the right shows the difference with incremental painting.
Incremental mode is a tool option that is shared by several brush tools, except those which have a ‘rate’ control, which
automatically implies an incremental effect. You can set it by checking the Incremental checkbox in the toolbox for the
tool (Paintbrush, Pencil and Eraser).
Indexed Colors
Indexed color mode is a mode for encoding colors in an image where each pixel in the image is assigned an 8-bit color
number. The color which corresponds to this number is then put in a table (the palette). Changing a color in the palette
changes all the pixels which refer to this palette color. Although you can create images in Indexed Color mode and can
transform images to it, it is, strictly speaking, not a color model.
See also the Indexed Palette section and the Convert Image to Indexed Colors command.