| 主权项 |
1. A method performed by a computing device, the method comprising:
receiving an image file, the image file having a set of pixels arranged in a grid, each pixel of the set of pixels having a plurality of color components; for each pixel of a subset of the set of pixels:
for a first color component of the plurality of color components:
predicting a value of the first color component of that pixel using a first prediction technique to yield a first predicted color value, the first prediction technique including median edge detection; andcomputing a difference between the first predicted color value and the value of the first color component to yield a first error value for that pixel;for a second color component of the plurality of color components, the second color component being distinct from the first color component:
predicting a value of the second color component of that pixel using the first prediction technique to yield a second predicted color value;predicting the value of the second color component of that pixel using a second prediction technique to yield a third predicted color value, the second prediction technique lacking median edge detection, the second prediction technique utilizing inter-component prediction with respect to the first color component;selecting whichever of the second predicted color value and the third predicted color value is closer to the value of the second color component to yield a selected predicted color value; andcomputing a difference between the selected predicted color value and the value of the second color component to yield a second error value for that pixel; andencoding the first error value for that pixel and the second error value for that pixel in a compressed color image output stream; writing the compressed color image output stream to persistent storage as an output compressed image file; and for each pixel of the subset of the set of pixels:
for a third color component of the plurality of color components, the third color component being distinct from the first color component and the second color component:
predicting a value of the third color component of that pixel using the first prediction technique to yield a fourth predicted color value:predicting the value of the third color component of that pixel using the second prediction technique to yield a fifth predicted color value, the second prediction technique utilizing inter-component prediction with respect to the first color component;predicting the value of the third color component of that pixel using the second prediction technique to yield a sixth predicted color value, the second prediction technique utilizing inter-component prediction with respect to the second color component;estimating an error for the fifth predicted color value based on a sum of first color component error values for a set of pixels adjacent to that pixel, the sum being weighted according to a Euclidian distance of each adjacent pixel from that pixel;estimating an error for the sixth predicted color value based on a sum of second color component error values for the set of pixels adjacent to that pixel, the sum being weighted according to the Euclidian distance of each adjacent pixel from that pixel;computing a weighted average of the fifth predicted color value and the sixth predicted color value, the fifth predicted color value being weighted by the estimated error for the sixth predicted color value and the sixth predicted color value being weighted by the estimated error for the fifth predicted color value, to yield an average color value;selecting whichever of the fourth predicted color value and the average color value is closer to the value of the third color component to yield another selected predicted color value; andcomputing a difference between the other selected predicted color value and the value of the third color component to yield a third error value for that pixel; andencoding the third error value for that pixel in the compressed color image output stream. |
