Fuji Fuji Sensor electronic processing.

Ianmac

New Member
Real Name
Ian Macdonald
I am new to this forum but have a Fuji X-M1, X-E2 and just purchased an X-T1.
I have all of Ricos ebooks on the above.
I do not have a clear picture of how the electronics work and if I could get this it would greatly assist me in using the camera.
What I really need is an electronic block diagram of the sensor, amplifier, DAC and Digital processor and how it interconnects with the camera controls particularly ISO and EV.
I am a retired engineer with background in electronics.
I am quite comfortable with the explanation of the Fuji Sensor and its following analogue amplifiers whose gain is controlled by the ISO setting.
Given the sensor can only respond to the light hitting it, controlled by aperture and shutter, and the electronic signal thereafter increased to an amplitude dictated by the ISO setting (controlling the gain of analogue amplifiers).
The optimum signal to noise ratio will be achieved at ISO 200 and the electronic signal from the sensor at its optimum level, requiring no additional amplification. Unity gain ?
At this point I assume the signal amplitude is at its maximum ( and optimum ) level for further processing in the analogue to digital converter. ( an allowance will be in place for a %age overload in the ADC )
Rico mentions both analogue and digital amplification take place?
Once the signal is in the digital domain amplification is a mathematical process. I am quite conversant with this and can see why that will be needed in any processing of the digital signal, for example the conversion to JPEG or processing the RAW data in Lightroom.
Can I ask two questions.
Where, prior to the formation of the RAW datafile does the digital amplification take place.
Where does the EV control operate ? in the analogue domain or the digital domain.
Any guidance will be appreciated
Many thanks
Ianmac
 

Lightmancer

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Bill Palmer
Ian, welcome.

Just one question from me. In the same way that understanding the exact workings of the engine under the bonnet of my car doesn't make me a better driver, I struggle to see why the sort of insight you seek will really make a difference to your use of your cameras or, more fundamentally, to the images you produce from them? There may be others on here who can answer your question in technical terms - I confess I am curious to see if there are - but speaking for myself I'm more interested in what the tool does than in how it does it.
 

flysurfer

Hall of Famer
Digital amplification is a simple digital multiplication in the camera or in the RAW converter. Or both.

Analog amplification and A/D conversion is already done on the Sony sensor.
 

Ianmac

New Member
Real Name
Ian Macdonald
Bill,
If you know how something works you can maximise its potential.
Rico
I appreciate from your book that the analogue amplifiers follow the sensor but in your book my reading is that you say that amplification occurs at both analogue and digital levels. I find it difficult to understand why further gain is required at digital level in compiling a RAW data stream ?
Quite comfortable with gain or attenuation or other processing after the RAW data stream to establish the user required format of the JPEG file
You cover how the ISO facility works but little mention of how the EV control works. Perhaps if you can tell me how/ where the EV control operates within the electronics it may help me see the full operation from sensor to output
Do FUJI have any more technical info available ?
regards
Ianmac
 

Amin

Hall of Famer
@Ianmac,

EV setting effects depends on camera mode.

If you are in aperture priority with a fixed ISO, EV setting will affect shutter speed and therefore exposure.

If you are in shutter speed priority with a fixed ISO, EV setting will affect aperture and therefore exposure.

If you are in manual mode with a fixed aperture and shutter speed but auto-ISO, then EV setting will affect ISO, which in turn affects analog gain.

I am not aware of any digital gain being applied prior to raw conversion in these cameras - Rico can clarify.

What generally does hold true for these particular cameras (and all those using modern Sony sensors) is that for a given exposure (aperture and shutter speed), the final image quality is similar whether you shoot at a high ISO in camera or instead choose to shoot at a low ISO in camera and push digitally to the same "equivalent ISO" as the high ISO.

Say for example that you shoot at f/1.4, 1/30s, EV set to 0, and the camera chooses ISO 6400. Next you shoot at f/1.4, 1/30s, EV set to -4 the camera chooses ISO 200. If you then push the latter file by 4 stops during RAW processing, the two resulting images will look much the same. The difference for practical purposes is that the native ISO 6400 file (large analog gain) risks irrevocably clipped highlight data in the raw file, whereas the ISO 200 in-camera JPEG (and EVF/LCD display) show a dark image.
 
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flysurfer

Hall of Famer
As I wrote, digital amplification is just math. Multiplication. You can multiply levels before and after the RAW data is written. Analog amplifications happens on the sensor, with separate A/D converters for each line (so there are quite many of them). This results in a short signal distance and makes the sensor isoless (less read noise).
 

Ianmac

New Member
Real Name
Ian Macdonald
Rico
I'm quite comfortable with digital and analogue signal processing.
Are you contradicting what you say in your book?
"Higher ISO settings dont increase the sensors sensitivity.The sensor in your XE2 is calibrated to its native ISO200 and this remains the same nomatter what ISO you set in the Camera"
Above you say analogue amplification happens on the sensor.
Do you mean analogue amplification is applied via the analogue amplifiers following the sensor in the total "sensor electronic chip" ( which also contains the A/D circuitry )

Amin
I agree with the 3 operational modes of the EV control. Manual mode was what I was questioning in my mind - was there any link to the book mention of analogue and digital gain as in my first post.
The EV control is operative in the analogue domain when in manual and Auto ISO is activated i.e. it is effectively doing the same as the ISO control by over riding the auto ISO selection circuitry and forcing it to fixed gain steps on the analogue amplifier(s).
This negates any processing in the digital domain ?
Like you I can see no need for digital gain in the preparation of the Raw file. If we are wrong Rico can clarify.
many thanks

Ianmac
 

Lightmancer

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Bill Palmer
Bill,
If you know how something works you can maximise its potential. ...

Ian, I totally understand that, provided that by gaining that insight you are then in a position to either adjust how your camera works or adjust your working practices to optimise your use thereof. In this instance I am still struggling to see what benefit you derive from this knowledge - as I said before how will it influence your use of your cameras and have a beneficial impact on the images you produce from them?
 

Ianmac

New Member
Real Name
Ian Macdonald
Bill
I suppose its a lifetime of being an Engineer, If I know whats going on inside I can drive it better and without continual recourse to manuals and books which sometimes contain misleading info.
Some lovely images on your website.
Ian
 

Amin

Hall of Famer
"Higher ISO settings dont increase the sensors sensitivity.The sensor in your XE2 is calibrated to its native ISO200 and this remains the same no matter what ISO you set in the Camera"

If the XE2 sensor applies the same analog gain regardless of nominal ISO setting, that would be different than all of the Sony/Nikon/Pentax cameras which also use APS-C Sony sensors. See: Sensorgen - digital camera sensor data
 

Lightmancer

Legend
Location
Sunny Frimley
Real Name
Bill Palmer
Bill
I suppose its a lifetime of being an Engineer, If I know whats going on inside I can drive it better and without continual recourse to manuals and books which sometimes contain misleading info.
Some lovely images on your website.
Ian

Thanks Ian. I'm not deliberately being obtuse, but I am not by inclination of a technical mind-set. It would be fair to say that I learned photography by the empirical method and have journeyed long and far to arrive in "Fujiworld". The cameras, lenses and most importantly the outputs of which they are capable please me both in use and when the images are hung on the wall. I have never opened a camera manual in my life, nor have I cared about the colour of the programmer's socks; as long as I can exert the control that I want and need, and use that control to consistently arrive at the results I want, that is good enough for me.
 

flysurfer

Hall of Famer
"Higher ISO settings dont increase the sensors sensitivity.The sensor in your XE2 is calibrated to its native ISO200 and this remains the same no matter what ISO you set in the Camera"

If the XE2 sensor applies the same analog gain regardless of nominal ISO setting, that would be different than all of the Sony/Nikon/Pentax cameras which also use APS-C Sony sensors. See: Sensorgen - digital camera sensor data

From what I have read in Germany, this 16 MP Sony sensor stops applying analog gain somewhere beyond ISO 640 / 800. Of course, that's information that isn't of much practical use for our daily shooting, but at least it suggests that if there are any visible differences between analog and digital amplification, they would/should appear between ISO 200 and 800. So if you select ISO values beyond 800, the sensor would be completely ISOless from this point on. Even most Canon sensors are ISOless beyond higher ISO settings (1600 or higher, I reckon).

It may be interesting to note that while Fuji doesn't write actual RAW data beyond ISO 1600 in all current APS-C cameras (leaving and additional multiplication to the RAW converter), this may very well change in the next sensor/processor generation.
 

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