Trim Mean Difference
trim-md
The trim-md parameter is the mean difference threshold for the trimming operation, and is only valid when trim=auto.
The default value is 11. This value defines the difference between each row of pixels while attempting to remove the border. Decreasing the threshold makes the imgix trim algorithm more aggressive about trimming. A decreased trim-md value may still leave a line or two of border on an image, usually due to noise in the borders from image compression.