Removing artifacts from document images

A computing device comprising:

• one or more processors;
• and
• one or more computer-readable media having instructions stored thereon that, responsive to execution by the one or more processors, causes the one or more processors to implement a shadow removal module of an image editing application configured to perform operations comprising:
• accessing a digital image;
• dividing the digital image into multiple local blocks;
• clustering pixel intensities of each of the local blocks into two or more clusters, the two or more clusters corresponding at least to a graphics color and a background color within each of the local blocks;
• clustering pixel intensities of the entire digital image into two or more clusters corresponding to at least to a graphics color and a global background color of the digital image;
• determining a global reference background color from color intensities in the cluster corresponding to the global background color of the digital image by comparing the color intensities to a representative background color;
• generating a per-pixel scaling factor that maps pixels of the background colors in the local blocks to the global reference background color;
• and
• applying localized adjustment of color intensity to the pixels of the background colors in the local blocks to remove artifacts from the digital image using the per-pixel scaling factor.

In a digital image editing environment, a method implemented by a computing device, the method comprising:

• accessing, by the computing device, a digital image in an image editing application;
• dividing, by the computing device, the digital image into multiple local blocks;
• generating, by the computing device, histograms for each of the multiple local blocks, the histograms representing a sample of a number of pixels of particular color intensities in each of the multiple local blocks;
• for each of the histograms of the multiple local blocks, using a Gaussian Mixture Model (GMM) by the computing device to cluster the histograms into two or more clusters;
• determining, by the computing device, pixels of the digital image that make up background intensities by upsampling pixels from one of the clusters of each of the multiple local blocks;
• generating, by the computing device, an aggregated histogram for multiple blocks of the digital image, the aggregated histogram representing a number of pixels of particular color intensities in all of the multiple blocks combined;
• using, by the computing device, the GMM to cluster the aggregated histogram into two or more clusters;
• determining, by the computing device, a global reference background color from the particular color intensities of the multiple blocks by comparing the each of the particular color intensities of the multiple blocks to a representative background color of the digital image;
• generating, by the computing device, a shadow map that comprises a per-pixel scaling factor that maps the pixels of the digital image that make up background intensities to the global reference background color;
• and
• applying, by the computing device, localized adjustment to the pixels of the digital image that make up background intensities to remove artifacts from the digital image using the per-pixel scaling factor.