Standard: | ISO 17957 — Shading measurements |
Technical Committee: | ISO/TC 42 Photography |
Published: | 2016-04-01 |
Image Quality Factor: | Uniformity |
ISO 17957 has been implemented in the Imatest Uniformity and Uniformity Interactive (UI) modules, starting with Imatest 2020.2, to be released late 2020, available in the Imatest Pilot program prior to the release. Uniformity measurements can also be accessed from Blemish Detect. All of these modules analyze flat-field images.
To obtain ISO 17957 calculations from Uniformity or UI, Special calculation (which can also be set to none or CPIQ) should be set to ISO 17957 and Grid size should be set to 11×11, as shown below in the Settings (or More settings) window. Click OK at the bottom of the window (not shown) to proceed with the run.
Portion of Settings window for Uniformity or Uniformity Interactive (UI)
After Uniformity or UI has been run, results are available in the Grid plot or new Grid contour map. Here is an example of the Grid contour map, which is particularly nice for visualizing results. We have selected L* (one of many selections available).
Grid contour map for L* in Uniformity Interactive.
ISO 17957 results are shown on the right, below the image.
The complete results as illustrated in Appendix B.2 of the standard are in the JSON output tile. We show a portion here.
"iso_17957_comment1": "The following results are displayed when ISO 17957 is selected.", "iso_17957_comment2": "They follow Annex B of the ISO 17957 Standard.", "iso_17957_comment3": "RGB values are in sRGB color space (sRGB is specified in ISO 17957).", "Red_pixel_values": [ [188.2,197.1,204.7,209.7,212.7,213.3,211,205.7,198.1,188.9,176.2], ... [165.9,177,185.6,191.5,194.2,195.1,193.5,189.1,181.7,170.7,157.8] ], "Green_pixel_values": [ [198.8,208.7,216.5,221.6,224.4,224.9,222.7,217.6,209.7,199.6,187.9], ... [173.2,184.1,192.3,197.9,200.9,201.9,200,195.6,188.5,177.5,164.1] ], "Blue_pixel_values": [ [196,205.2,212.9,217.8,220.6,221.2,218.9,213.9,206.1,196.5,184.5], ... [167.9,178.3,186.7,192.5,195.2,196.3,194.6,190.4,183.2,172.3,159.6] ], "CIE_X": [ [0.5112,0.5682,0.6178,0.6513,0.6713,0.6751,0.6596,0.6245,0.5744,0.5154,0.4462], ... [0.3776,0.4337,0.48,0.5134,0.5304,0.5363,0.5258,0.4999,0.4587,0.4003,0.3365] ], "CIE_Y": [ [0.5112,0.5682,0.6178,0.6513,0.6713,0.6751,0.6596,0.6245,0.5744,0.5154,0.4462], ... [0.3776,0.4337,0.48,0.5134,0.5304,0.5363,0.5258,0.4999,0.4587,0.4003,0.3365] ], "CIE_Z": [ [0.5112,0.5682,0.6178,0.6513,0.6713,0.6751,0.6596,0.6245,0.5744,0.5154,0.4462], ... [0.3776,0.4337,0.48,0.5134,0.5304,0.5363,0.5258,0.4999,0.4587,0.4003,0.3365] ], "CIE_L": [ [79.3,82.78,85.55,87.36,88.37,88.56,87.77,85.93,83.15,79.57,75.24], ... [70.1,74.13,77.15,79.22,80.28,80.64,79.97,78.37,75.76,71.72,66.78] ], "CIE_a": [ [79.3,82.78,85.55,87.36,88.37,88.56,87.77,85.93,83.15,79.57,75.24], ... [70.1,74.13,77.15,79.22,80.28,80.64,79.97,78.37,75.76,71.72,66.78] ], "CIE_b": [ [79.3,82.78,85.55,87.36,88.37,88.56,87.77,85.93,83.15,79.57,75.24], ... [70.1,74.13,77.15,79.22,80.28,80.64,79.97,78.37,75.76,71.72,66.78] ], "D_ci_chrominance_deviation": [ [0.6826,0.2253,0.1792,0.0568,0.167,0.1954,0.1524,0.1124,0.1408,0.5855,0.2179], ... [1.79,2.011,2.08,2.114,2.097,2.067,2.115,2.066,1.977,1.944,1.973] ], "RGB_Average": [199.2,211.2,207.4], "Lab_Average": [83.6,-4.762,0.4732], "Lab_Max": [91.75,-3.094,2.076], "Lab_Min": [66.78,-5.563,-0.3475], "D_L_Lightness_nonuniformity": [27.21], "D_Y_Luminance_nonuniformity": [33.92], "D_c_Chrominance_nonuniformity": [2.115], "D_Total_Colour_nonuniformity": [25.2],
Summary results-only are in the CSV output file.
The following results are displayed when ISO 17957 is selected. | |||
They follow Annex B of the ISO 17957 Standard. | |||
RGB values are in sRGB color space (sRGB is specified in ISO 17957). | |||
Full results (big arrays) are in the JSON output. | |||
RGB_Average | 199.17 | 211.18 | 207.37 |
Lab_Average | 83.6 | -4.76 | 0.47 |
Lab_Max | 91.75 | -3.09 | 2.08 |
Lab_Min | 66.78 | -5.56 | -0.35 |
D_L_Lightness_nonuniformity | 27.21 | ||
D_Y_Luminance_nonuniformity | 33.92 | ||
D_c_Chrominance_nonuniformity | 2.11 | ||
D_Total_Colour_nonuniformity | 25.2 |
Equations
\(\displaystyle \text{Lightness nonuniformity} = D_L = \max[L^*(i)]-\min[L^*(i)]\)
\(\displaystyle \text{Luminance nonuniformity} = D_Y = \frac{\max[Y(i)]-\min[Y(i)]}{\max[Y(i)]} \times 100\%\)
\(\displaystyle \text{Chrominance deviation for region } i = D_c(i) = \sqrt{[a^*(i)-\text{mean}(a^*)]^2 + [b^*(i)-\text{mean}(b^*)]^2}\)
\(\displaystyle \text{Chrominance nonuniformity} = D_c = \max[D_C(i)]\)
\(\displaystyle \text{Total color nonuniformity} = D_{Total} = \sqrt{(L^*_{\max}-L^*_{\min})^2 + (a^*_{\max}-a^*_{\min})^2 + (b^*_{\max}-b^*_{\min})^2]^2}\)