Use -colorspace HSV to convert the image to HSV. Next, select one sRGB color and convert it to HSV and offset its values low and high to generate the start and stop HSV colors. This returns the outline of the yellow flower petals: The lower values form the start color and the higher values form the stop color. Start by choosing one sRGB color (somewhere on the image - in this case the yellow of the flowers) and offset it low and high to form two sRGB colors. The following are some typical examples of use: To illustrate how color thresholding performs, use this image: convert input-image -colorspace XXX -color-threshold 'start - stop' output-image For a color image, you would likely not find too many gray pixels. But these two colors are black and white and so map only to a range of grayscale as hsv(0,0%,0%) and hsv(0,0%,100%). For example, one might naively think that sRGB(0,0,0) to sRGB(255,255,255) would produce a white image, catching all colors, even when using -colorspace HSV. A large range in one colorspace may map to only a narrow range in another colorspace.

However, a range of colors that spans hue = 0 may still be useful, if the start hue value is higher than the stop hue value.Ĭaution is advised when mixing the colorspace of the start and stop colors and that of the image. Note that Hue is cyclical - 0 and 360 are the same. For colorspace Gray, be sure to use a start value lower than the stop value. Start and stop colors can be specified in any colorspace (recognized by ImageMagick), but in general, we advise you specify them in the colorspace corresponding to the -colorspace option.

Use the -colorspace to perform the thresholding in an alternative colorspaces (currently limited to sRGB, Gray, HSV, HSL, HCL, HSB, and HSW). Thresholding, by default, take place in the sRGB colorspace. The two colors are separated with a hyphen between them. All colors between the start and stop colors (inclusively) become white and the rest of the image pixels become black. Use color thresholding to specify a color range and return a black and white image.

Imagemagick replace color