Analyzing scene SBR with an app

radiant · Feb 27, 2021

I implemented a concept app which purpose is to easily get understanding of scene subective brightness range (SBR). It works as any other mobile light meter except it analyses the scene in blocks. Idea is that it can measure parts of the scene like using 100 spot meter readings at the same time.

Here are some screenshots of the prototype. First line shows EV(100) min-max range.

Next line (f-stop range) is just the difference of max-min. This is the beef of the project.

"expose" - row is the suggested exposure (in EV(100)) calculated in traditional mobile light meter app style. The values in parenthis are just differences to the first row values).

The block color coding is following: cyan = highest EV, blue=lowest EV, grayscale coding = black is low EV and whiteish = high EV.

I would like to hear your thoughts of this idea; worth of developing further or ready to go down to the trash?

Also please go ahead and write down ideas if you have any; I can try them out on this prototype.

The app is implemented on iOS so it is currently iPhone only app. If you are interested testing this idea please send your email to me and I can attach you to TestFlight program which allows distributing app before releasing.

radiant · Feb 27, 2021

My own analysis of the samples:

View to the street: f-stop range 10.9 is probably correct. Typical scene where you cannot get shadow & highlight details on same frame in normal exposure & development.

Window view: range 8.4 stops; probably right too. One can squeeze some details from inside without pushing details outside to the shoulder?

Shelf view: range 5 stops; easy peasy to capture. Typical indoor scene SBR?

bnxvs · Feb 27, 2021

This is a good idea. It is a pity that only for ios. I think, this program need to work on cheap Android smartphones. Then it will be a useful tool for LF

Horatio · Feb 27, 2021

Cool idea!

radiant · Feb 27, 2021

bnxvs said:
This is a good idea. It is a pity that only for ios. I think, this program need to work on cheap Android smartphones. Then it will be a useful tool for LF

Thanks! Yes the target is for LF use of course but of course gives some insight for other format photographers too.

radiant · Feb 27, 2021

Horatio said:
Cool idea!

Nice to hear. I was hesitating and questioning this myself

vickersdc · Feb 27, 2021

I like this... the only problem I might have is that I'm still using an iPhone 5 with IOS10.3... does the app work with this version?

radiant · Feb 27, 2021

vickersdc said:
I like this... the only problem I might have is that I'm still using an iPhone 5 with IOS10.3... does the app work with this version?

I got it compiled on iOS 10.3 so it should work on your phone too.

edit: However I don't know if TestFlight supports that iOS. If I publish this app, then it should run on iPhone 5.

Lachlan Young · Feb 27, 2021

I'd suggest using the IRE scale to tie highlight or shadow exposure keying to - ie brightest highlights with detail are placed 2 1/3 stops over where a direct reading would place them, or darkest shadows with detail are placed 2 2/3 stops under where a direct reading would place them. Offer the user the option as to which to key to.

radiant · Feb 27, 2021

Lachlan Young said:
I'd suggest using the IRE scale to tie highlight or shadow exposure keying to - ie brightest highlights with detail are placed 2 1/3 stops over where a direct reading would place them, or darkest shadows with detail are placed 2 2/3 stops under where a direct reading would place them. Offer the user the option as to which to key to.

Do you mean that for example in the street view example where brighest part is measured 15.7 user could choose that app suggest exposure at 13.3 ?

edit: That would be 1.5 stops more exposure than what is calculated from the whole scene (14.8)..

koraks · Feb 27, 2021

Your ideas are always interesting, and likewise, this one is also worthy of further pursuit!
I'll think about it some more and post back if I have any suggestions.

distributed · Feb 27, 2021

This is a great project!

I thought about developing something similar to sharpen my perception of SBR, but then never got around to it. I also wanted to do it web based, but I would suspect that the necessary brightness information (how bright is an LSB?) is not present and the image might have been processed in various ways.

If you still have some space, I'd like to be on your test flight program. You already have my email address

radiant · Feb 27, 2021

koraks said:
Your ideas are always interesting, and likewise, this one is also worthy of further pursuit!
I'll think about it some more and post back if I have any suggestions.

Thanks koraks, I was already thinking that you might have some ideas in your sleeve!

distributed said:
This is a great project!
I thought about developing something similar to sharpen my perception of SBR, but then never got around to it. I also wanted to do it web based, but I would suspect that the necessary brightness information (how bright is an LSB?) is not present and the image might have been processed in various ways.

Thank you!

Hmm, I didn't even look could this done with javascript. Probably could be done I had the light measurement app ready from previous project so this was quite easy extension to that. And yes, you are on the testers list for sure

Anyone else with iPhone and willing to play around with this, send me your email..

warden · Feb 27, 2021

Excellent work!

One suggestion related to human factors would be to consider using colors that are farther apart on the color wheel than blue and cyan which would allow people that struggle with color perception [raises hand] to more easily read the graphic information.

I'll PM you my email.

Craig75 · Feb 27, 2021

11 stops in the first picture seems far too much. The others look right to me but that first one seems very high.

Def keep going with it tho - this is a very good project.

radiant · Feb 27, 2021

Craig75 said:
11 stops in the first picture seems far too much. The others look right to me but that first one seems very high.

I hope tomorrow is similar bright day, I can then check with my spot meter how these app value compare.

The day was really bright today when I took that capture. Really clear sky and some areas in good shadow (dark trees) and all calculations are done with same algoritm. So that might be or might not be correct.. We will see benchmark this idea for sure!

Thank you all (so far) for so nice comments, I've got some betatesters too!

Sirius Glass · Feb 27, 2021

I invite you to do that in brighter areas such as the US southwest deserts and red rock areas. There SBR of 14 are not unusual.

Craig75 · Feb 27, 2021

vedostuu said:
I hope tomorrow is similar bright day, I can then check with my spot meter how these app value compare.

The day was really bright today when I took that capture. Really clear sky and some areas in good shadow (dark trees) and all calculations are done with same algoritm. So that might be or might not be correct.. We will see benchmark this idea for sure!

Thank you all (so far) for so nice comments, I've got some betatesters too!

could specular highlights in snow be tricking the meter? (that's a random totally unsubstantiated guess)

how many stops does an iphone camera sensor have? We see a top notch 35mm digital sensor top out around 14 stops but what is the range on a phone? Random uneducated guess is 10.9 stops is the max range of the phone sensor without HDR activated and something is tricking the app. That could be complete garbage tho

Cool idea tho - i literally said someone needs to make an app like this on the new spotmeter thread just last week

MattKing · Feb 27, 2021

This looks really interesting.
One point regarding nomenclature - although I have in the past always used Scene Brightness Range (SBR) I've been told that the correct term is actually Scene Luminance Range, which has the unfortunate acronym of SLR.

radiant · Feb 27, 2021

Sirius Glass said:
I invite you to do that in brighter areas such as the US southwest deserts and red rock areas. There SBR of 14 are not unusual.

Great excuse to come by, I just might be busy photographing than testing the app there

Craig75 said:
how many stops does an iphone camera sensor have? We see a top notch 35mm digital sensor top out around 14 stops but what is the range on a phone? Random uneducated guess is 10.9 stops is the max range of the phone sensor without HDR activated and something is tricking the app. That could be complete garbage tho

Ah yes. Probably limitations hitting the wall. At that SBR level the app is probably already quite useless. There isn't any trickery on that part since the light calcualtion is done from single exposure. It might be possible to make multiple exposures and then get larger range..

Craig75 said:
Cool idea tho - i literally said someone needs to make an app like this on the new spotmeter thread just last week

Wow! I was thinking about ZS yesterday and thought if ever there was any device which could measure everything automatically. I usually first think of a new device until I (again) find out that I have everything needed in my pocket..

ic-racer · Feb 27, 2021

The brightness range is of secondary importance in B&W photography compared to the exposure. Scene brightnoess range, of course, has never been a criteria for exposure of B&W negative materials.

Of course the shadows are used for exposure, based on the work of Nelson and Jones (which were subsequently incorporated into ASA and then ISO).

Does this app allow one to set the exposure based on the shadow areas? I don't expect you to fix a "K" value but the sophistocated user, that understands what is going on, should be able to set their own "K" value based on their own Zone I testing.

Craig75 · Feb 27, 2021

vedostuu said:
Great excuse to come by, I just might be busy photographing than testing the app there

Ah yes. Probably limitations hitting the wall. At that SBR level the app is probably already quite useless. There isn't any trickery on that part since the light calcualtion is done from single exposure. It might be possible to make multiple exposures and then get larger range..

Wow! I was thinking about ZS yesterday and thought if ever there was any device which could measure everything automatically. I usually first think of a new device until I (again) find out that I have everything needed in my pocket..

I think you will have to use hdr function to eliminate specular highlights from the reading. We know not to point a spotmeter at glaring metal etc but the app doesnt know that. Im assuming comparing multiple exposures will help see what is specular highlight and disregard it from the sbr range. Otherwise there will be occasions where the app greatly overestimates the range.

Lachlan Young · Feb 27, 2021

vedostuu said:
Do you mean that for example in the street view example where brighest part is measured 15.7 user could choose that app suggest exposure at 13.3 ?

edit: That would be 1.5 stops more exposure than what is calculated from the whole scene (14.8)..

Is that 15.7 the brightest area with detail or pure white? I'd also recommend working on basing the exposure off a shadow index as ic-racer suggested - if you have a Pentax spot meter or one that has IRE indexing available, I'd take a detailed shadow reading, index to IRE 10 ('1' on the Pentax) and see if that value can be set up to be recognised by the app as the important metering point. Shadow values are often surprisingly stable.

Sirius Glass · Feb 27, 2021

OR just take a spot meter and point it at the brightest location with detail and then the darkest location with detail and compare the two. No app needed.

takilmaboxer · Feb 27, 2021

My spot meter died and I can't afford a new one. So I carry the light meter over to the bright area and then into the shadowed area and make measurements. Works great.
Actually after so many years of shooting in the Southwest and Rockies I can anticipate the values pretty accurately. A bit of bracketing and I'm sure to get a good negative, especially with films like TM400 that have a 14 stop straight line

Analyzing scene SBR with an app

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