Multi ISO HDR single shot without dual-iso interpolation/artifacts

[Guillermo Luijk]

Following the same DR enhancement principle as used in dual-ISO, different ISO values could be user-defined for different horizontal areas of the sensor according to the scene, in a similar way GND filters do but far more configurable:




The DR enhancement can be up to 3 stops but interpolation is not needed in this case, so the loss of quality and issues found in dual-iso captures cannot take place.

The captured RAW data needs to be previously processed reducing RAW levels on the ISOs above ISO100 in order to have a final RAW file with uniform RAW levels (the same as those found in the lowest used ISO).

Sorry if this idea has already been posted or some technical reason makes it impossible to implement.


Regards

[dfort]

When you go from a group of lines that are one ISO to another group of lines that are a different ISO wouldn't that cause a hard line? How are you going to blend them? Even if you could get intermediate ISO values less than 1/3 stop (which I believe you can't) you would get banding on large flat areas of the image. I'm not saying that it is impossible but it might not be very practical. Graduated ND filters can be rotated to different angles, your proposal would only work like a filter stuck in the horizontal position.

[Guillermo Luijk]

There would be no bands. All the areas are to be corrected to match the ISO100 exposure before saving the final RAW file like dual-ISO does with the high ISO values.

I.e.
RAW values from ISO200 must be divided by 2
RAW values from ISO400 must be divided by 4
...

This is not a GND filter emulation, it's a way to obtain an enhanced DR linear RAW file by increasing SNR with ISO. I just mentioned GND filters because of the division of the scene in different luminance horizontal layers.

Regards

[Greg]

This is not possible.

The solution, buy a Nikon/Sony/Pentax/Samsung camera and do it in a postprocess.

[Guillermo Luijk]

Why is it not possible if dual-ISO, much more complex, is possible?

[dfort]

Sorry, I didn't understand your feature request. Still don't.

I also don't understand why Nikon/Sony/Pentax/Samsung cameras would be the solution if you have to do it in post.

Maybe you should explain the issues you have with Dual ISO. From my experience it seems to be working very well.

[Guillermo Luijk]

Dual ISO needs interpolation in the deep shadows and in the highlights which can end in loss of resolution and artifacts.

This method would only be valid in certain scenes (like the ones where a GND filter is), but requires no extra interpolation, just the standard Bayer RGGB, so you have both the full resolution of a standard capture and the DR of dual-ISO.

Regards

[DeafEyeJedi]

Do you have a photo (preferably original unconverted CR2) that shows exactly that issue you're referring to?

[Guillermo Luijk]

You mean me? I don't even have a Canon body with ML sorry. Anyway the loss of resolution in dual-ISO is a fact because of the strong interpolation needed, right?. The opposite would just be miraculous.

Regards

[Walter Schulz]

I also don't understand why Nikon/Sony/Pentax/Samsung cameras would be the solution if you have to do it in post.

ISO-less cameras. It doesn't matter if you run ISO 100 in cam and push it up to 1600 in post or shoot 1600 in cam -> Both the same.

[josepvm]

Gullermo, as far as I know, it is not possible to set different ISO values to arbitrary areas of the sensor in a single shot. Only two values for alternate rows. And that's because Canon hardware is designed that way.

In Canon DSLRs there are two independent readout circuits for odd rows and even rows. And Magic Lantern is able to set a different ISO to every circuit tweaking the values in some CMOS registers, but can't do anything to choose a different ISO distribution across the sensor surface.

If you have not read it already, you can take a look at this paper for a more detailed explanation.

[josepvm]

A possible alternative approach for what you are requesting was found here: http://www.magiclantern.fm/forum/index.php?topic=12523.0

Using Magic Lantern's feature "Full resolution silent pictures", the electronic shutter introduces vertical gradient for shorter exposures. Something similar to a graduated filter, caused by the rolling shutter. A1ex found a formula to quantify it, so perhaps it would be possible to correct it in post, allowing an expanded dynamic range for landscapes.

[Audionut]

Dual ISO doesn't do anything with the sensor, it controls some devices further down the chain. 

It just so happens that Canon designed these devices in a way that they process data from the sensor in an alternating pattern, and so they were exploited to produce dual  ISO.

[Guillermo Luijk]

Gullermo, as far as I know, it is not possible to set different ISO values to arbitrary areas of the sensor in a single shot. Only two values for alternate rows. And that's because Canon hardware is designed that way.

OK this is the key. I thought the sensor readout gain could be individually set for every row of photosites. Not being this possible my approach is nonsense.

Regards!