Author Topic: CMOS/ADTG/Digic register investigation on ISO (Read 866149 times)

Audionut · « **Reply #175 on:** January 19, 2014, 06:29:12 PM »

2 images, 1 with lens attached and 1 with lens unscrewed. Both at f/4.0 to ensure no secret gain changes.
Both developed with the same settings in ACR. Camera faithful profile, no noise reduction, no lens correction, as shot color temperature.
Layered in PS with a difference layer blend on the top layer.

Only difference is the slight shot positioning error.

Quote from: Greg on January 19, 2014, 04:13:13 PM

unmount lens (So that the contacts do not touch.):

mount lens :

Ouch.

5D3.

a1ex · « **Reply #176 on:** January 19, 2014, 07:22:40 PM »

500D: log2(10.71)-log2(8.62) = 0.31 stops of ISO boost at f1.4, apparent ISO 100->124
DR 10.492-10.486 = 0.006 => real ISO 100->100.5

5D3: log2(7.24)-log2(6.57) = 0.14 stops, apparent ISO 100->110
DR 10.976-10.952 = 0.024 => real ISO 100->101.6

Apparent ISO: image brightness in JPEG preview and maybe at default settings in a raw editor.
Real ISO (by DxO definition, that is, from clipping point) assummes correct white level handling by the raw editing software.
If the raw editor assumes some fixed white level and clips everything above it, apparent ISO will be closer to reality.

According to DxO, the difference can be noticeable at f1.2. Any volunteer to check it?

You don't need ML to run the test; simply take a test picture at f1.2 with the lens normal and then with the lens unscrewed from the body, compare the highlights and measure noise stdev from the left optical black area. Or just upload the two CR2's.

Quinton · « **Reply #177 on:** January 19, 2014, 08:56:58 PM »

Any particular settings? ISO etc as its night time here.
I have an 85mm 1.2 here, and also have a canon cinema lens T1.3 if that helps any.

a1ex · « **Reply #178 on:** January 19, 2014, 09:05:01 PM »

Yes, M mode, ISO 100, aperture wide open, and the image should include clipped highlights (e.g. a light bulb). Same settings in both (only change screwed vs unscrewed).

Quinton · « **Reply #179 on:** January 19, 2014, 10:03:18 PM »

4 images uploaded to dropbox as I don't seem to be able to upload to forum.
First 2 are from the 85mm 1.2 1st with data 2nd unscrewed
Second lot are using the canon cinema 50mm T1.3 not sure if they will help with any comparisons.
If these are not what you require let me know and I can try other shots.

https://dl.dropboxusercontent.com/u/49168208/85mmf1.2.CR2
https://dl.dropboxusercontent.com/u/49168208/85mmunlockedf1.2.CR2

https://dl.dropboxusercontent.com/u/49168208/50mm-t1.3.CR2
https://dl.dropboxusercontent.com/u/49168208/50mmunlockedt1.3.CR2

a1ex · « **Reply #180 on:** January 19, 2014, 10:18:54 PM »

From the first two:

Noise 7.0886 vs 6.1815 => ISO was boosted by 0.2 stops

DR 10.98 vs 11.06 => you lost 0.08 stops of highlights because of Canon's trick. Not really noticeable in practice.

If you have an APS-C body, the difference may be a higher (DxO suggests 0.5 stops).

Quinton · « **Reply #181 on:** January 19, 2014, 10:35:24 PM »

Maybe the image wasn't the best, would you rather have something say black then a candle beside it to make sure the whole dr is covered?
DXO says that the real light for that particular lens is T1.4

Will be interesting to hear regarding the cinema lens, as there should not be any "trickery" needed by canon.

a1ex · « **Reply #182 on:** January 19, 2014, 10:48:06 PM »

For black, each CR2 has an optical black area (that's where I'm measuring noise). For a visible difference, some gradient pattern (gradual transition to clipped white) would be better.

The shots with the cinema lens were not taken at the same shutter speed.

Quinton · « **Reply #183 on:** January 19, 2014, 11:47:06 PM »

Here's a couple more from the cine lens T1.3 with same shutter speed.
Not the sharpest, as hand holding and trying to get it to clip at a low shutter speed, hope that will be OK, can take better ones during the day tomorrow with a tripod if needed.

https://dl.dropboxusercontent.com/u/49168208/50mmt1.3.CR2
https://dl.dropboxusercontent.com/u/49168208/50mmt1.3locked.CR2

engardeknave · « **Reply #184 on:** January 19, 2014, 11:57:56 PM »

I also have the 85 1.2 on a 5D2 if that would be useful.

a1ex · « **Reply #185 on:** January 20, 2014, 12:56:17 AM »

50mm t1.3:

Noise 7.11 vs 6.16 => iso boost 0.2 stops
white 16383 vs 15283
DR 10.98 vs 11.07 => highlights lost 0.09 stops

Would be great if you could take this shot on tripod, so I could do a side-by-side comparison of the images.

edwmotion · « **Reply #186 on:** January 20, 2014, 02:48:22 AM »

7D 50mm f1.2 pentax, can I help?

Greg · « **Reply #187 on:** January 20, 2014, 03:17:45 AM »

Quote from: edwmotion on January 20, 2014, 02:48:22 AM

7D 50mm f1.2 pentax, can I help?

I don't think so. The camera needs to know that it has connected the lens and the current aperture.

Quinton · « **Reply #188 on:** January 20, 2014, 02:04:05 PM »

Quote from: a1ex on January 20, 2014, 12:56:17 AM

50mm t1.3:

Noise 7.11 vs 6.16 => iso boost 0.2 stops
white 16383 vs 15283
DR 10.98 vs 11.07 => highlights lost 0.09 stops

Would be great if you could take this shot on tripod, so I could do a side-by-side comparison of the images.

Not sure you are experimenting with the right things.
2 images below set all in manual and using the latest firmware 1.2.3
I can tell from the histogram before shooting that whenever you unscrew the lens slightly that its clipping sooner.
I had to move the clipped light from 1/40th to 1/20th to get it to clip in histogram when it was clipping at 1/40th when locked
Both shots taken exact same settings.
50mm T1.3

https://dl.dropboxusercontent.com/u/49168208/locked.CR2
https://dl.dropboxusercontent.com/u/49168208/unscrewed.CR2

a1ex · « **Reply #189 on:** January 20, 2014, 02:19:23 PM »

Quote from: Quinton on January 20, 2014, 02:04:05 PM

I can tell from the histogram before shooting that whenever you unscrew the lens slightly that its clipping sooner.

Histogram before shooting is not exact (even ML raw histogram in LV it's an approximation). Histogram *after* shooting (e.g. in RawDigger) is the one you should look at.

a1ex · « **Reply #190 on:** January 20, 2014, 02:30:49 PM »

I have some good news for 5D2 (credits go to Greg, he found it on 500D):

- SaturateOffset register works and I have moved the black level from 1024 to 64.
- According to my 5D3 theory, this would be equivalent to reducing ADTG gain by -0.091 EV (ISO 100->94).
- However, the dynamic range in raw_diag is showing an improvement of over 0.7 stops at ISO 100 (!)

What's going on?!

edit: diagnosed. In some Canon cameras, bad pixels are marked as 0 in the raw buffer (and then interpolated). In raw_diag, I was not doing any checks of the raw pixel values (so, a bunch of zeros compared to 1024 were bumping stdev a lot more than the same bunch of zeros compared to 64).

The real improvement was close to 0.1 stops, so the theory about Saturate Offset is still valid.

Updated raw_diag to skip hot pixels:

raw_diag.mo (source: raw_diag.c)

(the bad pixel modification should be backported to ML raw.c)

Audionut · « **Reply #191 on:** January 20, 2014, 03:47:33 PM »

I have this sick obsession with tweaking things. Hence the nut at the end of audio

vs Canon vs mini_ISO

Off now to take some sample images and see what the change is visually.

Audionut · « **Reply #192 on:** January 20, 2014, 04:41:03 PM »

I have sighted bias, so I would like some opinion on these 2 test images before I give my own.

1

2

edit: I can still see, what I think I can see, in these resized and JPG (minimum) compressed images. I can upload sample CR2s at a later date if requested.

Quinton · « **Reply #193 on:** January 20, 2014, 05:01:38 PM »

I'm no expert and its hard to tell online but picture 2 for me seems noisier than 1 and the colours are flatter, or maybe I'm just seeing things because I'm expecting a difference.

lasfede · « **Reply #194 on:** January 20, 2014, 05:17:38 PM »

I see a clear difference in colours but not in terms of noise, may be the contrast of picture 1 is weaker which leads to less noise. I prefer colours of shot 2, shot 1 seems to be more red.

Greg · « **Reply #195 on:** January 20, 2014, 05:36:26 PM »

Nikon 500D :

Audionut · « **Reply #196 on:** January 20, 2014, 05:59:13 PM »

PM response is in favour of image 1. In my opinion, this image has less banding noise. Check the blurred background left and right of the colorchecker. It's easier to see in full res CR2.

This image (1) is with these settings.

Further testing favours a digital gain value of 462.

Note: This is only with ISO 100, and only tested with a 5D3 (Greg would be interested to see results with 500D).

Quinton · « **Reply #197 on:** January 20, 2014, 06:15:18 PM »

Quote from: Audionut on January 20, 2014, 05:59:13 PM

PM response is in favour of image 1. In my opinion, this image has less banding noise. Check the blurred background left and right of the colorchecker. It's easier to see in full res CR2.

TBH both images were pretty noisey, just no2 was more so.
I have only seen noise like that at much higher ISOs or where they have been considerably pushed in post processing.

Greg · « **Reply #198 on:** January 20, 2014, 06:18:31 PM »

In practice, the difference is not so big.

Canon 500D (-3EV ACR):

Nikon 500D (-3EV ACR):

Crop 1:1 (+2,5EV ACR):
Canon 500D :

Nikon 500D :

Audionut · « **Reply #199 on:** January 20, 2014, 06:32:16 PM »

Quote from: Quinton on January 20, 2014, 06:15:18 PM

I have only seen noise like that at much higher ISOs or where they have been considerably pushed in post processing.

I expose so that the white patch (in the colorchecker) is exposed as high as possible before over exposure. The images in the above test are exposed 5EV lower with shutter, and increased 5EV in post. Note: This should put the black patch around -9.7EV. I WB and brightness correct from a correctly exposed image. This removes any error due to noise, and obviously, ensure lighting remains consistent.

To be clear, image 2 was an ISO calibrated mini_iso result. And the difference was always going to be minor, because I've already shown the gains being made with just ADTG tweaks.

The quickest way to see any differences, is with images down near the noise floor IMHO.

When I get time to sort out a 32bit (ACR limited to +/-5EV) raw based workflow, I'll test further into the noise floor

News:

Author Topic: CMOS/ADTG/Digic register investigation on ISO (Read 866149 times)