Gray component replacement in a digital image to generate a color transformed image

A printing device comprising:

• a printhead;
• a pixel gradient engine to analyze a plurality of pixels of a digital image to determine gradients corresponding to each pixel of the plurality based at least in part on a pixel value of each pixel;
• a frequency engine to generate, based on the gradients corresponding to each pixel of the plurality, a high frequency map for the digital image that indicates an amount of high frequencies corresponding to each pixel of the plurality;
• an activity mask engine to generate an activity mask for the digital image based on the high frequency map for the digital image, the activity mask including an activity value for each pixel;
• an image processing engine to process the digital image by performing gray component replacement based at least in part on the activity mask to generate a color transformed image corresponding to the digital image;
• and
• a print engine to print the color transformed image with the printhead.

A non-transitory machine-readable storage medium comprising instructions executable by a processing resource of a computing device to cause the computing device to:

• analyze a plurality of pixels of a digital image to determine multiple gradients corresponding to each pixel of the plurality based at least in part on a pixel value of each pixel;
• generate an activity mask based on a magnitude and direction of each gradient of the multiple gradients corresponding to each pixel of the plurality, the activity mask comprising an activity value for each pixel of the digital image and identifying at least one granular area of the digital image that comprises a set of pixels having relatively higher activity values;
• and
• process the digital image with the activity mask to generate a color transformed image by performing adaptive gray component replacement in the at least one granular area of the digital image.