The disclosure provides a method, device, and readable storage medium for adjusting image quality. The display device system selects a focus area of a target image, and outputs a mapping relationship curve of an input luminance value and an output luminance value of the target image. Then, an input luminance value range of pixels in the focus area of the target image is calculated, and upper and lower edge coefficients of the input luminance value range are proportionally adjusted to obtain new upper and lower edge coefficients. The mapping relationship curve is adjusted according to the new upper and lower edge coefficients, thereby adjusting the focus area of the target image.