Author Topic: CMOS/ADTG/Digic register investigation on ISO  (Read 557807 times)

Sganzerla

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1100 on: April 26, 2019, 11:05:37 PM »
I'm interested in this technique to make my low light footage 'cleaner' so made 3 tests without any conclusion of the real benefits with my 5D MKIII, no crop mode.

The last test I made (ISO 3200) was puting ADTG Preamp to 2 (Default is 85 in my camera and not 52 as in the video) and ADTG 0xFE to 3 resulting ISO 1648. When exporting the .mlv and using ACR to make the adjustments I found no improvement after matching the brightness of both files - normal and with iso_reg.
If I turn camera off and on again, the resulting ISO changes to 1923 without touching anything!

My questions are:
 - Is this the right way to test this module?
 - Is the turn off/on 'resulting ISO' change expected?
 - I haven't touched the shutter/aperture dials in my latest test, they were the same, was it the wrong approach?

PS: If there was a video showing how to use dual iso the proper way as @70MM13 video showed how to use this module, it would be very cool.

70MM13

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1101 on: April 27, 2019, 01:12:56 AM »
the settings i use are strictly for iso 200.  it won't be optimal for any other iso.

i have a feeling that there will be no benefit for iso 3200, but you will have to experiment to find any setting that helps.

good luck!

Luther

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1102 on: April 27, 2019, 04:46:42 AM »
i have a feeling that there will be no benefit for iso 3200, but you will have to experiment to find any setting that helps.

I think Canon's ISO goes from range 100 to 1600. Above that it uses digital push. @a1ex could correct me if am wrong here.

Audionut

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1103 on: April 27, 2019, 01:06:54 PM »
- I haven't touched the shutter/aperture dials in my latest test, they were the same, was it the wrong approach?

These registers predominately affect highlights.  You gain highlight headroom.  If you don't change exposure settings, you simply increase the space between signal max and sensor saturation.

I think Canon's ISO goes from range 100 to 1600. Above that it uses digital push.

Depends entirely on the camera.  5DIII is good to ISO 3200.

Luther

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1104 on: April 27, 2019, 01:48:00 PM »
Depends entirely on the camera.  5DIII is good to ISO 3200.

Couldn't understand the Table A2. Can you explain? From 1600 to 3200 it has a drop in DR and double more noise, from what I got from this table...

Code: [Select]
  noise           (electrons)  (e/DN)    ISO
 16.86                2.655    0.157    3200
 31.76                2.501    0.079    6400

Sganzerla

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1105 on: April 28, 2019, 07:18:49 AM »
Thanks for the insights guys, will take a more refined closer look at this topic again.
English is not my native language so sometimes the technical aspects are harder to understand.

Audionut

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1106 on: April 28, 2019, 11:00:54 AM »
Can you explain?

Table 1

Code: [Select]
  ISO   Apparent   Maximum   DR
         Read      Signal
         Noise

  1600   3.6        4050    10.1
  3200   2.7        2030     9.6
  6400   2.5        1000     8.6

Apparent Read Noise.

From ISO 1600 to ISO 3200 (one full stop), the DR only decreases by 0.5EV.  Thus, you throw away the full stop of highlights from the ISO bump, but you gain 0.5EV in the shadows.  Backed up visually in table 2a and 2b.

From ISO 3200 to ISO 6400, you don't gain anything (except more accurate exposure in camera).  A full stop of highlights has been thrown away, but the DR has also reduced by one full stop.  You didn't gain any signal in the shadows (the entire point of bumping ISO).


histor

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1107 on: June 09, 2019, 09:00:15 PM »
This month I was testing reduced analog gains on 5d2 while everyday shooting and results look great. In short: it looks like we can pull down iso100 to something about iso20-25 still having full dynamic range (up to 11.6).

Setup.
Reddeercity’s builds for 5d2 + raw_diag.mo

As Alex once reported, it’s reasonable to pull these DFE values from 48x down to 250 – until vertical banding becomes very noticeable. I’ve tried lower values and subtracted darkframes in post. Luckily vertical banding stays constant for the same ISO and DFE values. I don’t know whether it is important or not, but I used CMOS[0]=0x200, 0x204, 0x208 to get the darkframes (for iso 100, 200 and 400 respectively). Either it’s some physically stable bias (hard to believe that) or just the factory calibration playing against us. I keep just 3 master-darks, they work without a problem. Final images after subtraction show no FPN and very low random noise (reason 1 - analog amplifiers may generate a lot of noise themselves; reason 2 – longer exposure gives larger number of photons).

At DFE values about 100 raw_diag reports worse DR. We can see shadow clipping (posterised green shadows) in post. 111 was just my safe random choice. It turns selecting of iso 100-200-400 to something about iso 20-40-80. All look unbelievably clean. Iso800 is out of use here (it’s produced with DFE values 0x8xx). Iso1600 is a digital push.
SHAD_GAIN (c0f08030) set to 0xfff disables digital push for wide apertures. Not a great change, but still useful.
 
Attaching 2  samples of processed images (shadows lifted a lot) and some raws to play with. “-df” in filenames means that I’ve already subtracted blacks with Pixelfixer (I like its CR2-IN > CR2-OUT approach).

Known problems.
The only way to see overexposure is looking for pink highlights. Auto-ETTR can’t catch it but raw_diag.mo works perfectly.
Low analog gains may be used with Dual-ISO module (or simply patching CMOS[0]=0x343 for iso100/400). But final images are not always recognized by cr2hdr-20bit. Using –force gives processed images with striped lights. Attaching samples, didn’t tried it much.
Works also with Reddeercity’s video hacks (14bit raw, don’t forget darkframes) but adtg_gui.mo is an overkill here – it takes a lot of resources (and power?) and a lot of time for setup. No way to save its settings. Not a run-and-gun tool. What we need to emploi low iso range is a tiny separate module, patching DFE values at start. Maybe just on/of and a choice of value for them. Unfortunately I’m not the one to write it.

Checked the same approach with 600d. It gives something, but nothing groundbreaking yet.

Test raw files - https://app.box.com/s/d7i3qj09pc300ffb73sgrtnj7totjc7i

Audionut

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Re: CMOS/ADTG/Digic register investigation on ISO
« Reply #1108 on: June 12, 2019, 01:20:39 AM »
In short: it looks like we can pull down iso100 to something about iso20-25 still having full dynamic range (up to 11.6).

This can be thought as a digital reduction of ISO.  Yes, you have used an analog amplifier, but you haven't increased the cameras ability to capture more photons.

To determine if there is any positive effect to reducing the analog gain this much, you would need to measure the signal to noise ratio of the resulting images.  Did you reduce the noise in the ouput (increase SNR), or did you simply turn the volume knob down and create a bunch of known problems processing the resulting files?