We have analyzed the properties of metals in the high redshift intergalactic medium using a novel objective pixel optical depth technique on a sample of extremely high signal-to-noise Keck HIRES and ESI spectra of 26 quasars between redshifts 2.1 and 6.4 . The technique relies on using the doublet nature of the common ions C iv and Si iv that are the principal metal tracers in the intergalactic medium outside of the Ly \alpha forest . Optical depths are statistically corrected for contamination by other lines , telluric absorption , bad pixels , continuum fitting , etc . and for incompleteness , and we achieve in this way an increased sensitivity of approximately 0.5 dex over previous analyses . As with existing pixel optical depth analyses , the method is completely objective and avoids subjective cloud selection and Voigt profile fitting , but , unlike existing techniques , we do not compare the ion optical depths with H i optical depths to determine the ion optical depth distributions ; we therefore avoid problems arising from different velocity widths in the ion and H i . We have shown how the conventional analysis can be reproduced using a percolation method to generate pseudo-clouds from ion optical depths . Using this set of pseudo-clouds , we have generated C iv column density distributions and have confirmed that the shape of the C iv column density distribution remains essentially invariant , with slope -1.44 , from z = 1.5 to z = 5.5 . This in turn confirms the lack of redshift evolution of \Omega ( { CIV } ) for z = 2 to z = 5 , both for all absorbers with column density , \log N = 12 - 15 and for stronger absorbers with \log N = 13 - 14 . The generation of pseudo-clouds from the optical depth vectors also gives information on the column density environment of a given optical depth . We find that for the higher resolution HIRES data there is a tight relation , \tau \sim N ^ { 0.7 } , between the peak optical depth and the column density . We have then analyzed the ion redshift evolution directly and model-independently from the optical depth vectors themselves and show that there is little evolution in the total amount of C iv from z = 2 to z = 5 , though there is a turndown of at least a factor of two in \Omega ( { CIV } ) above z = 5 . We do , however , see substantial evolution in the ratio , Si iv/C iv . In two subsequent papers in the series , we will use this technique to investigate what fraction of the absorbers lie in galatic wind outflows ( Paper II ) and what metallicity is associated with regions of \tau ( { Ly } \alpha ) < 1 ( Paper III ) .