Leica Adding a "Gamma Curve" to a digital image: Thinking out Loud and Experiments


I've made the statement in the past that the M Monochrom has the lowest non-uniformity of any sensor that I've used. The low-noise level is amazing. I've looked at the numbers using custom code, but never generated metrics on performance. That- I used to do for digital sensors in the early 1980s.

After several years, I can verify that comment.

This table is from the above website, the last two columns are dark signal non-uniformity (DSNU) and Photo Response Non Uniformity (PRNU) is - like Fixed Pattern Noise (FPN) - a way of expressing errors in the output from sensors. The lower the value, the better the raw image. I will never sell my M Monochrom, or M9. My M8 is one of the last in the production line. I'll keep it as well. 35 years ago- would have selected the M Monochrom based on the last two columns alone.

Camera ModelISOBlack
Level
Range
Black
Column
Metric
Black
Row
Metric
Illuminated
Column
Metric
Illuminated
Row
Metric
DSNU ▾PRNU



Leica CL1000.1110.0040.0150.0150.0106%0.4%
Leica CL[HCG]4000.1380.0040.0080.0050.0069%0.4%
Leica M (Typ 240)2000.0280.0090.0050.0100.005213%2.0%
Leica M (Typ 262)2000.0330.0060.0040.0140.007327%0.6%
Leica M Monochrom3200.0970.0040.0290.0040.0086%0.1%
Leica M Monochrom (Typ 246)3200.0080.0130.0080.0100.03986%0.5%
Leica M-D (Typ 262)2000.0310.0130.0060.0080.00794%0.5%
Leica M81600.0410.0050.0060.1570.0126%5.1%
Leica M91600.1400.0050.0050.0070.0065%0.4%
Leica M101000.0790.0060.0090.0060.00657%0.3%
Leica M10 Monochrom1600.0500.0110.0210.0060.00529%0.2%
Leica M10 Monochrom[HCG]8000.0410.0110.0110.0050.00435%0.4%
Leica M10-P1000.1190.0070.0090.0220.01074%0.4%
Leica M10-R1000.0840.0130.0200.0070.00636%0.3%
Leica M10-R[HCG]4000.0350.0070.0100.0060.00441%0.4%
Leica Q (Typ 116)1000.3030.0050.0560.0140.00813%0.8%
Leica Q2500.0640.0070.0090.0180.00812%0.4%
Leica Q2[HCG]8000.4140.0040.0070.0050.00520%0.7%
Leica S-E (Typ 006)1000.3050.0050.0090.0240.0114%0.6%
Leica S (Typ 007)1000.0760.0390.0260.0300.01541%0.4%
Leica SL (Typ 601)500.6800.0100.0610.0090.00714%0.6%
Leica SL (Typ 601)[HCG]2000.3120.0120.0150.0050.00523%0.5%
Leica SL2501.5870.0040.0100.0200.0139%0.3%
Leica T1000.0050.0050.0060.0210.00711%0.4%
Leica TL1000.0040.0050.0050.0180.01113%0.4%
Leica TL21000.0000.0040.0040.0240.01352%0.3%
Leica X11000.1350.0040.0050.0300.10672%0.4%
 
Last edited:

ph.

New Member
Real Name
Paul
Thanks, most illuminating.
In the 1960es Kodak published a paper on why an S curve was best. Less computation, but more labour intensive: shading and burning, waving hands in the light cone when enlarging plus suitable choice of exposure and development ,or decades later, similar imprecise and laborious work in photoshop.would achieve better brightness balance .

My generation was taught "Algol-60" and I have given up on anything except ready-to- run subroutines on W-10 or "deb" packages with all dependecies, so I am not optimistic about the possibility of compiling such code to run on my computers.

p
 
I ported this code to Windows using the Watcom V2 Fortran-77 compiler recently, so I can insert the SD card and run directly. The current version also interpolates over an under-performing line- not dead. I have it hard-coded to my sensor now, will make it more flexible. An alternative to sending the M Monochrom to Leica for remapping. I'll also add a switch for generating the Gamma curve DNG.
 

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