The bright tone range is a separate measurement. It can quickly check the middle tone during or after printing. In G7, HR replaced TVI to check the overall lightness and darkness and gray balance, but TVI is still useful for controlling the chroma of printing presses.
HR needs to be measured twice, one is CMY (HR_cmy), and the other is single black (HR_k). In the absolute value measurement state, each measurement is performed once (two times in total). Measure three times (a total of 12 times), and then compare HR with TVI, HR will give a more obvious mid-dark tone and contrast, because HR is measured in absolute form, and TVI is measured in relative form.
Simply put, HR is expressed in ND (neutral density), which can be measured when the spectrophotometer is set to the black channel or "image density". ND can also be measured by CIEXYZ_Y. In fact, the official measurement of GRACOL neutral ash is according to:
ND = log10 (100 / Y); (Y? 0≤100)
Measuring HR_cmy
Measure the neutral density of the composite CMY color patch (50C, 40M, 40Y), and then subtract the paper density to get HR_cmy.
HR_cmy = ND (50C, 40M, 40Y)-ND (paper = 0.54 (typical)
For devices with a variation range of about 1.3ND or higher, HR_cmy will be a constant 0.54. For devices with a low variation range, such as newsprint printing, HR_cmy may be lower. HR_cmy can also be calculated automatically by IDEAlink software.
Measuring HR_k
HR_k is obtained by measuring the 50K color patch density value and then subtracting the paper density.
HR _k = ND (50K)-ND (paper) = 0.50 (typical)
For devices with a dynamic range of approximately 1.3ND or higher, HR_k will be a constant 0.50. For devices with low dynamic range, such as newsprint printing, HR_k may be lower. HR_k can also be calculated automatically by IDEAlink software.
Note: Before February 2006, GRACOL 7 stipulated that HR_k = HR_cmy, and in February 2006, in order to comply with the ISO12647-2 TVI curve, HR_k was reduced to 0.50. If you use the CMY NPDC curve to correct NPDC single black, you need to use HR_cmy (0.54) to match HR_k instead of 0.50.
HR absolute value
For special paper, if the paper density is also included in the HR, then the absolute HR density of the special paper can be obtained, and only one gray block needs to be measured to control HR.
For example: if the paper ND = 0.09, HR = 0.54 HR
Absolute density = 0.09 +054 = 0.63 (only for this type of paper)
L * units represents HR absolute density
If L * units is used instead of density to represent the absolute HR density, a Lab reading can be used to simultaneously measure gray balance and brightness. Standard paper with whiteness of L * 95, maximum blackness of 300% of 25L * (1.35ND) CMY color, maximum blackness of 16L * (1.7ND) 100K, absolute value of L * HR (retain one decimal place) :
HR_cmy absolute value = L * 57.5
HR_k absolute value = L * 59.9
The L * HR value of other papers can be calculated automatically by IDEAlink software.
Note: It is best not to use the "relative" L * value to represent or measure HR, because the spectrophotometer does not allow arbitrary calibration on any substrate, and if the paper is not the standard 95L *, then the new L * value does not significance.
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