Image forming apparatus and image forming method

An image forming apparatus comprising:

• a color converter for
• converting a cyan component, a magenta component and a yellow component of a first image signal comprising the cyan component, the magenta component, the yellow component and a first black component to equivalent neutral density,
• calculating a first gray component from an equivalent neutral density cyan component, an equivalent neutral density magenta component and an equivalent neutral density yellow component,
• subtracting the first gray component from each of the equivalent neutral density cyan component, the equivalent neutral density magenta component and the equivalent neutral density yellow component,
• subjecting each of the equivalent neutral density cyan component, the equivalent neutral density magenta component and the equivalent neutral density yellow component from which the first gray component is subtracted to an inverse conversion of a conversion to the equivalent neutral density, and
• outputting a second image signal comprising a cyan component, a magenta component and a yellow component which are obtained by carrying out the inverse conversion to the equivalent neutral density cyan component, the equivalent neutral density magenta component and the equivalent neutral density yellow component from which the first gray component is subtracted, the first black component and the first gray component;
• an image forming section for forming an image on a paper based on the second image signal by using a cyan toner, a magenta toner, a yellow toner, a black toner and a gray toner;
• and
• a controller for controlling the color converter and the image forming section, wherein
• brightness of a cyan toner simple color image that has maximum chroma is between 53 and 70,
• brightness of a magenta toner simple color image that has maximum chroma is between 31 and 51,
• chroma of a gray toner simple color image is equal to 10 or less, and brightness of the gray toner simple color image is between 30 and 90.