Monday, March 8, 2021

DOFIS: Traffic Light Augmented Information

It seems these days that Artificial Intelligence (AI) is finding its way into nearly every part of our lives, and that includes photography. There is an obvious trend towards 'computational photography' and cameras or add-on devices that 'do the work' of the photographer, eg choosing 'scene-informed optimum' settings.

Whist such trends are to be expected, for many photographers, the idea of having a machine take over our craft leaves a nasty taste in the mouth.

But as usual, there is a middle ground, using what I call 'Augmented Information' (AuI).

Augmented Information doesn't take the decisions away from the photographer, but provides enhanced information from which decisions can be made. That is enhanced information that the manufacturer decided not to give us!

Being a Magic Lantern shooter means I can create my own AuI.

The hyperfocal distance is clearly a piece of information, processed from various pieces of 'data', eg focal length, aperture value and our choice of the infinity defocus blur that is acceptable, ie the so-called circle of confusion (CoC).

But when I'm focus bracketing, clearly I need additional information, ie augmented information, to help me know where to focus for the next focus bracket. 

I wrote the DOFIS script to provide such AuI, ie to alert the photographer that you are at or close to the 'optimum' place to take the next focus bracket: but it's your choice if you wish to take an image at that point.

In the current version of DOFIS this feedback is provided through colours, ie: yellow meaning I'm at the same point of focus as the last captured image; red meaning I've opened up a focus gap beyond the criterion I set; and green meaning that I have a positive focus overlap.

This AuI feedback is provided in the Quick Shooting screen as well as in LV. For example:

Up until now the weaknesses with the LV feedback, but not the QS feedback, is that it is restricted to a very small part of the screen, ie at the top right of the ML LV information bar. Looking at the screen in normal viewing conditions all will be OK, go out into the bright sun and/or place the camera low, say, relative to your eyes, and things become difficult to see.

For this reason I'm pleased to announce that DOFIS now has a traffic light AuI feature, that is designed to be readable in any viewing conditions.

The DOFIS menu now looks like this:

Here we see that I've switched off focus bracketing feedback, ie the colour changes in the ML upper bar, and selected the new feature called Traffic Lights. As I'm shooting with my visible band 5D3, I've also deselected IR frequency; although as I've switched off diffraction awareness, this is rather academic.

The new feature has two Traffic Lights:

In the above screen grab from the video, we see, in the top bar, that DOFIS is telling us we are in absolute  depth of field mode, ie an A between the near and far DoFs, ie 28cm and 34cm. That we are using a split, ie thick, lens model (S), that diffraction aware is off (-) and that we need to take about 4 brackets from where we are (31cm) to reach the hyperfocal. Finally we see a green box with 86%, this is an MTF50 figure of merit estimate of the diffraction based resolution degradation, relative to shooting at the largest aperture and at infinity: for more information on this metric see and

The left hand traffic light shows information on the status of the current focus position, relative to the last captured image, ie yellow means the current focus is at the same place as the last captured image; red means there is a focus gap and green means a positive focus overlap. The overlap criterion is that set in the ML CoC, ie 20um in this test.

The right hand traffic light shows information on the status of the infinity defocus blur. Red means that the infinity blur is greater than the overlap criterion, ie the ML CoC value, ie you are focused at less than the (overlap) hyperfocal distance; yellow means that you are focused at between the hyperfocal and three times the hyperfocal, ie giving an infinity blur between the overlap setting and a third of this; green means that you are beyond three times the hyperfocal and less than infinity; finally black means you are at infinity, so beware, ie there is no data here!

Each traffic light contains an additional piece of data. The left hand one tells you the defocus blur, in microns, at the overlap point.

The right hand traffic light tells you the infinity defocus blur in microns, ie the green line below, shown relative to the set CoC (30um in the chart below):

To illustrate how the new AuI feature works, I've recorded a short video of me undertaking a test focus bracket set: starting in Quick Shooting, non LV mode; switching to LV mode; composing, and setting focus to the minimum, at which point the upper bar shows the DoF info (in this case absolute distances from the sensor); taking the focus brackets; and finally coming out of LV mode, ie returning to QS mode.

The choice of overlap blur is yours. In the video above I chose 20 micron as I then have some focus insurance that helps with my workflow, ie as soon as the left hand traffic light goes red, I know I'm at a sensible focus position for the next image, ie greater than 20 micron, but not by much. Using this workflow means I don't need to worry about ensuring the left hand traffic light is green; just going red is OK.

As for when to stop focus bracketing. The right hand traffic light tells me this, ie when I'm less than the overlap blur, and not at zero, where there is no real data.

In the above test, the blurs at the 2nd, 3rd and final images were: [23/97], [23/49],[19/10]. Clearly showing that the overlap blurs are well behaved and that the infinity blurs progressively approach the final infinity defocus value of 10 microns.

The traffic lights are reset by either changing focal length or aperture.

As usual I welcome any feedback on the DOFIS traffic light feature.

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