Here’s an updated version 0.8 of the tuning file. Corrected a few oversights, change some minor things. More details below.
{
"version": 2.0,
"target": "IMX477 v0.8 - by cpixip 2022",
"algorithms": [
{
"rpi.black_level": {
"black_level": 4096
}
},
{
"rpi.dpc": {}
},
{
"rpi.lux": {
"reference_shutter_speed": 27242,
"reference_gain": 1.0,
"reference_aperture": 1.0,
"reference_lux": 830,
"reference_Y": 17755
}
},
{
"rpi.noise": {
"reference_constant": 0,
"reference_slope": 2.767
}
},
{
"rpi.geq": {
"offset": 204,
"slope": 0.01078
}
},
{
"rpi.sdn": {}
},
{
"rpi.awb": {
"priors": [
{
"lux": 0,
"prior": [
2000,
1.0,
3000,
0.0,
13000,
0.0
]
},
{
"lux": 800,
"prior": [
2000,
0.0,
6000,
2.0,
13000,
2.0
]
},
{
"lux": 1500,
"prior": [
2000,
0.0,
4000,
1.0,
6000,
6.0,
6500,
7.0,
7000,
1.0,
13000,
1.0
]
}
],
"modes": {
"auto": {
"lo": 2500,
"hi": 8000
},
"incandescent": {
"lo": 2500,
"hi": 3000
},
"tungsten": {
"lo": 3000,
"hi": 3500
},
"fluorescent": {
"lo": 4000,
"hi": 4700
},
"indoor": {
"lo": 3000,
"hi": 5000
},
"daylight": {
"lo": 5500,
"hi": 6500
},
"cloudy": {
"lo": 7000,
"hi": 8600
}
},
"bayes": 1,
"ct_curve": [
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0.27424225990946918,
2200.0,
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2400.0,
0.5204264653110015,
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2600.0,
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2800.0,
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3000.0,
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3200.0,
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3400.0,
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4600.0,
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5600.0,
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6100.0,
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6600.0,
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7600.0,
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8100.0,
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0.9331696750390895,
8600.0,
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],
"sensitivity_r": 1.05,
"sensitivity_b": 1.05,
"transverse_pos": 0.0238,
"transverse_neg": 0.04429,
"coarse_step": 0.1
}
},
{
"rpi.agc": {
"metering_modes": {
"centre-weighted": {
"weights": [
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2,
2,
2,
1,
1,
1,
1,
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0,
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]
},
"spot": {
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2,
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1,
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]
},
"matrix": {
"weights": [
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1,
1,
1,
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1,
1,
1,
1,
1,
1,
1,
1
]
}
},
"exposure_modes": {
"normal": {
"shutter": [
100,
10000,
30000,
60000,
66666
],
"gain": [
1.0,
2.0,
4.0,
6.0,
8.0
]
},
"short": {
"shutter": [
100,
5000,
10000,
20000,
33333
],
"gain": [
1.0,
2.0,
4.0,
6.0,
8.0
]
},
"long": {
"shutter": [
100,
10000,
30000,
60000,
120000
],
"gain": [
1.0,
2.0,
4.0,
6.0,
12.0
]
}
},
"constraint_modes": {
"normal": [
{
"bound": "LOWER",
"q_lo": 0.98,
"q_hi": 1.0,
"y_target": [
0,
0.3,
1000,
0.3
]
}
],
"highlight": [
{
"bound": "LOWER",
"q_lo": 0.98,
"q_hi": 1.0,
"y_target": [
0,
0.3,
1000,
0.3
]
},
{
"bound": "UPPER",
"q_lo": 0.98,
"q_hi": 1.0,
"y_target": [
0,
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1000,
0.8
]
}
],
"shadows": [
{
"bound": "LOWER",
"q_lo": 0.0,
"q_hi": 0.5,
"y_target": [
0,
0.17,
1000,
0.17
]
}
]
},
"y_target": [
0,
0.16,
1000,
0.165,
10000,
0.17
]
}
},
{
"rpi.contrast": {
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"gamma_curve": [
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]
}
},
{
"rpi.ccm": {
"ccms": [
{
"ct": 2000,
"ccm": [
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]
},
{
"ct": 2200,
"ccm": [
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-0.45932286857238488,
-0.21373542690252199,
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-1.2660673594740142,
2.005654261091916
]
},
{
"ct": 2400,
"ccm": [
1.6766610071470399,
-0.5447101051688111,
-0.16838641107407677,
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1.592223692670396,
-0.2127091997471162,
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-1.1339155942419322,
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]
},
{
"ct": 2600,
"ccm": [
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]
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{
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},
{
"ct": 3000,
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1.596168842967451,
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]
},
{
"ct": 3400,
"ccm": [
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]
},
{
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"ccm": [
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},
{
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},
{
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},
{
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{
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},
{
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},
{
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},
{
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},
{
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},
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},
{
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1.4574646927117559
]
}
]
}
},
{
"rpi.sharpen": {}
},
{
"rpi.focus": {}
}
]
}
This new v 0.8 tuning file is based on the Raspberry Pi’s original tuning file.
The new v 0.8 tuning file features the following differences (in the order of appearance in the file) with respect to the original one:
CT-Curves
The new ct-curve is now based on the illumination spectrum of a black body radiator up to about 3600 K; for higher color temperatures, the CIE standard illuminant D is used. You notice the switch by the little kink in the blue curve below. That’s a difference from the previous version, which used black body radiator spectra over the whole range of color temperatures.
A further change happened in this section: I did reduce in this new file the “coarse_step” parameter from its default 0.2 to a value of 0.1 - as far as I understand it, the AWB will take slightly longer to converge, due to this change, but the sampling will be finer.
ALSC-section
This section is completely gone at the moment. The reason for this is that this section actually describes the current lens/camera combination. So it depends on the lens you are using at the moment. As the lens can be changed on the HQ camera, any data in the tuning file relating to the lens is most of the time not correct (only, if your lens happens to be the one used in the calibration).
Contrast Curve
I replaced the sRGB-contrast curve in my previous tuning file with the rec709 contrast curve in this version. rec709 is an industry standard. Here’s a plot of the difference
rec709 features a little bit less contrast than the contrast curve of the standard file. This has also an impact on color saturation. Images obtained with the v 0.8 tuning file will have slightly less color saturation than images captured with the standard file.
Furthermore, in the contrast-section the “ce_enable”-parameter is now set to zero in order to get rid of the automatic algorithm running in the background. Occasionally, users will have to tune the brightness and contrast controls by themselves, but I guess, users who care about tuning files know how to do this.
CCM-section
The CCMs in this section have been all calculated new and work in association with the new ct-curve introduced above. Generally, they vary much smoother than the values in the original tuning file. Here’s a plot of the principal red component of the CCMs over color temperature to show what I mean:
In the tiny range from 3700 K to 4000 K, the principle red component varies in the original file quite a bit, resulting in noticeable color changes within small deviations of the estimated color temperature. In contrast, the variation of the matrices components in the new tuning file is much smoother.
Conclusion
Well, this concludes the list of differences between the original tuning file and my current version.
Additional Hint
The Raspberry Pi Foundation indicated that soon HQ cameras will feature a slightly different IR-blockfilter, as the old one is no longer manufactured. From the information I have, I’d say the differences between the filters are minor. The Raspberry Pi Foundation already distributed a new IMX477 tuning file, claimed to “give best results with both old and new camera modules”. If you did an update on your Raspberry Pi software recently, chances are that you are already working with their new tuning file. The comparison plots above (the red curves) are already based on the new Raspberry Pi tuning file.
