Imagetrac Q-factor vs. IJG recompression comparison for image SA1_14

Shown are image as originally captured vs. recompression at IJG q-factor=25, along with three different 'diffs', or image subtractions of the two images. (See bottom of page for details)

Text links are 100dpi. Image links are full resolution.

Capture Q-values are 1-255. Higher value=*LOWER* resolution.

(Current default capture window = Window #1, Q=75.)

Hint: Use middle mouse button to bring up image in separate window for detailed comparison.

	no-recomp	q=25	diff=GRAY1	diff=GRAY2	diff=GRAY3
Capture Window #3 Q=50	3.14 sz=184516	3.14q25 sz=118731	3.14q25 sz=78086	3.14q25 sz=119861	3.14q25 sz=52049
Capture Window #1 Q=75	1.14 sz=145128	1.14q25 sz=118370	1.14q25 sz=45452	1.14q25 sz=87756	1.14q25 sz=36120
Capture Window #2 Q=100	2.14 sz=124952	2.14q25 sz=109804	2.14q25 sz=21627	2.14q25 sz=54466	2.14q25 sz=26137
Capture Window #4 Q=150	4.14 sz=103296	4.14q25 sz=102234	4.14q25 sz=40337	4.14q25 sz=73806	4.14q25 sz=33474

Description of Gray-scale differencing algorithms

GRAY1 - Difference RGB values after being converted to gray-scale. E.g., diffVal = G * abs(rgbToGray(rgb1)-rgbToGray(rgb2))

GRAY2 - 'Euclidean' distance between respective rgb values. E.g., diffVal = G * sqrt(rdiff^2 + gdiff^2 + bdiff^2)

GRAY2 - 'Euclidean' distance taken after converting RGB deltas to gray. E.g., diffVal = G * sqrt(deltaR2Y^2 + deltaG2Y^2 + deltaB2Y^2)

Where gray-scale values are magnified by a gain of G=2, and where the 'Y' of delta-2Y is a luminance value obtained via a lookup table for R,G and B respectively.

Note: all delta images are saved at IJG compressionfactor of q=40. This introduces some additional artifacts.