rawopint.lua: Fast, accurate intervalometer with raw exposure metering

c_joerg

1236

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #100 on: 07 / January / 2019, 09:34:50 »

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Quote from: Mlapse on 07 / January / 2019, 03:06:30

with rawopint it seems to only respond just after a shot has been made.

It also takes a long time for my M3 to finish rawopint. When I stop the recordings with menu on the M3 it takes a long time until the script is really finished. Feels like that for 20 seconds. On my G1x it finished much faster.

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Mlapse

539
S95 S110

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #101 on: 10 / January / 2019, 16:37:57 »

i was wondering with rawopint would it be possible to create a set of settings that would allow the following diagram in exposure time to be created?

I've found that most Canons set 1 sec exposure at around bv-400, here on the diagram at about bv-380.
in this diagram bv range runs from 380 to -620 (the red line), exposure from 1/100 to 1 sec.
Iso400 is fixed for this camera to keep the relation Tv/bv clear.

Idealy i would like it to reach 1 second exposure at bv-300, if i understand my math that is 1 full stop earlyer.
and i woudn't want it to overexpose at daylight. so that is why I drew the new set of exposure times from 1/60 to 1 sec.
but if it can be done -to keep it smooth- as a 1/3 stop change at 1/10sec-1/8sec (bv:0) or some other idea i would still be interested.

tested it and it's the worst idea i had in years.

What would you consider to be the best match in parameters/settings to create this smooth increase in exposure as things become darker?

« Last Edit: 13 / January / 2019, 13:58:00 by Mlapse »

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reyalp

13844

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #102 on: 10 / January / 2019, 17:12:37 »

Quote from: Mlapse on 10 / January / 2019, 16:37:57

Idealy i would like it to reach 1 second exposure at bv-300, but I'm guessing that is 3 stops earlyer.

Assuming you are using APEX*96 values, there's ~1 stop between -400 and -300.

The exposure parameters required to achieve "correct" exposure at a given Bv is defined by the APEX equation (http://dougkerr.net/Pumpkin/#APEX) : Av + Tv = Bv + Sv

Setting shutter to 1s (Tv 0) ISO 400 (Sv 7), and Bv to (BV96 = -300)/96 =~ -3
Av + 0 = 7 - 3
Av = 4 = F/4 (this is a coincidence, APEX Av and F number are not *generally* interchangeable, although the mid range is pretty close)

So if you want correct exposure at 1s to be Bv96 -400, set your aperture to F/4. If CHDKs idea of raw neutral is off on your camera (as it appears to be on the EOS Ms) you might want to shift it accordingly.

If you want rawopint to stop at 1s and 400 ISO, just set those limits. Without Bv/Ev shift, this should act a lot like scripts based on Canon AE, which the scene suddenly gets darker once the limits are hit. If you want it to fade more gradually, you should use Bv/Ev shift, which makes this more complicated, or manage the fade in post.

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Mlapse

539
S95 S110

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #103 on: 10 / January / 2019, 19:04:11 »

yes, sorry, i redid that 3 stop, but was too late for your answer.

but reading in on the link (thank you, will take some days to work it out.
what i'm thus asking is... ok, this is going to sound silly.

in my log it states that the first 1sec/iso400 shot was made at f3.1 bv-367 and that sound right according to that formula.

so my question should actually be, can we throw away that equation

when it gets dark and replace it with Av+1+Tv = bv +sv...although if it's that crude it wont work so the 1 in the equation should be in 1/3 steps

Oh, and get it back as soon as it turns day again....

ok, ok thank you for letting me understand what i'm asking.

« Last Edit: 10 / January / 2019, 19:17:40 by Mlapse »

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reyalp

13844

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #104 on: 10 / January / 2019, 23:55:30 »

Quote from: Mlapse on 10 / January / 2019, 19:04:11

in my log it states that the first 1sec/iso400 shot was made at f3.1 bv-367 and that sound right according to that formula.

Sorcery!

Quote

so my question should actually be, can we throw away that equation when it gets dark and replace it with Av+1+Tv = bv +sv...although if it's that crude it wont work so the 1 in the equation should be in 1/3 steps Oh, and get it back as soon as it turns day again....

Now I'm confused. What do you want to happen when it gets dark?
Adding 1 to the Av + Tv side is a negative exposure compensation, meaning darker than the "correct" exposure that the equation is defined for.

If you want the scene to get darker smoothly as the light level falls, that's what Bv / Ev shift is meant to do. However, the difference from your idea is that it's always active, in proportion to the difference between the "base bv" and the actual bv, rather than only kicking in at "night". It would probably be possible to make an option to only apply it below a certain Bv.

You could set the Bv / Ev shift base low, and let the meter high and overexposure limits control the high exposure.

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Mlapse

539
S95 S110

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #105 on: 11 / January / 2019, 04:34:22 »

I want the taken pictures to get dark more slowly between something like bv200 to bv-300....for now limited to 1 sec, that could be 4sec, 2 stops further if the camera and I permit that.
If that works i would expect then that s going from night to day 1 sec exposure would still be used until it reaches bv-300 (approx) and that it would change back to the original calculations between 1 sec and 1/60.

since the original calculation Av+Tv=bv+sv results in a specific exposure my first thought was to change that formula so it would allow for a longer exposure.
sort of cheating the camera in thinking it ~~is darker~~(not true bv values stay the same) uses a lower ISO than it actually is thus moving the exposure to a longer shot earlyer than expected.
using a multiplier on the calculated exposure time at set timings before shoot would probably also do it.

after some tests I can do the other way around, so cheating the calculated exposure by using an available higher iso and so shifting 1sec exposure to bv-500 or even lower bv values (bv-768 or darker @ max 1/4sec exposure @ any ISO you set before you started)....but that is completely opposite to what i want. This way in the images it gets darker more quickly. (alas a lower iso is lost in the dark)

and, more importantly, for my purpose it is too much to change 1 stop or more during a shoot (1/3 stop iso values, like 250 and 320 didn't gave stable results in my tests, but maybe i should do more).
it creates a too big a shift in how the image is illuminated..the actual shift should be no more than 1/3 stop per exposure time (so f.i. 1/3 shift at exposure 1/60, 1/30 and at 1/10, creating 1 full stop difference between 1/60 and 1 sec.)

btw this doesn't help astrophotography since the camera is still bound to it's absolute maximum exposure/iso values
and if you are bothered with +1 on the left, i can always shift it to the right side as -1

« Last Edit: 11 / January / 2019, 09:04:00 by Mlapse »

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reyalp

13844

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #106 on: 11 / January / 2019, 17:16:21 »

Quote from: Mlapse on 11 / January / 2019, 04:34:22

I want the taken pictures to get dark more slowly between something like bv200 to bv-300....for now limited to 1 sec, that could be 4sec, 2 stops further if the camera and I permit that.

That makes sense. This is what I created Bv/Ev shift for, but it operates somewhat differently: If you set the faction to say, 33% and base to 10 (daylight) then for every stop change in Bv away from broad daylight, there will be a 1/3 stop change in exposure in the same direction, subject to the limits imposed by other settings.

In practice, the scene won't get much brighter if Bv goes over the "base" value, because "correct" exposure is quite close to the point where the sensor clips, and the over exposure limits are set to keep things below that. However, rawopint might be more prone to flickering if it's bouncing off the limits.

Quote

since the original calculation Av+Tv=bv+sv results in a specific exposure my first thought was to change that formula so it would allow for a longer exposure.

The equation describes the values will produce "correct" exposure. If you want to diverge from "correct" exposure by some amount, you just have to add or subtract whatever you want from the terms you can control. Adding to Tv or Av is a negative "ev shift", i.e. shorter exposure or smaller aperture. Adding to Sv is positive shift (higher ISO).

Quote

sort of cheating the camera in thinking it ~~is darker~~(not true bv values stay the same)

To be clear, the APEX equation isn't code that we control in the camera, it's just a convenient way of expressing the relationship between the values. rawopint derives the logged "Bv" from the exposure parameters and how much the "meter" value diverges from the "neutral" value.

Depending on your workflow, you might consider different approach:
Instead of trying to make the script capture what you want to see in the video, expose everything as "correctly" (i.e. as bright as possible without clipping) and manage brightness in post processing based on logged Bv. Making a well exposed image darker in post will give you a better SNR than an under-exposed one, and you can choose how much you want to fade for a real brightness change after the fact. This would likely only make sense if you are shooting raw and have a workflow that can be programmed to digest data from the CSV files.

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Mlapse

539
S95 S110

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #107 on: 12 / January / 2019, 02:36:53 »

Quote

Depending on your workflow, you might consider different approach:
Instead of trying to make the script capture what you want to see in the video, expose everything as "correctly" (i.e. as bright as possible without clipping) and manage brightness in post processing based on logged Bv. Making a well exposed image darker in post will give you a better SNR than an under-exposed one, and you can choose how much you want to fade for a real brightness change after the fact. This would likely only make sense if you are shooting raw and have a workflow that can be programmed to digest data from the CSV files.

you are absolutely right in this but it will take up some time to realize that. luckely i've got some 3 month before i have a purpose for all i'm doing now...although i am also eager to use your snippet in another script.
so i just put on a test cam to see how it handels dawn(an a480, i hate to wear down the m10 for naught)

for rawopint my settings are 30% and base 10 at this moment and that seemed to work fairly well....

« Last Edit: 12 / January / 2019, 02:39:45 by Mlapse »

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c_joerg

1236

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #108 on: 12 / January / 2019, 02:51:05 »

Quote from: reyalp on 11 / January / 2019, 17:16:21

Instead of trying to make the script capture what you want to see in the video, expose everything as "correctly" (i.e. as bright as possible without clipping) and manage brightness in post processing based on logged Bv.

That is also my way I go. I do it similarly as described here
https://chdk.setepontos.com/index.php?topic=12790.0

Quote from: reyalp on 11 / January / 2019, 17:16:21

Making a well exposed image darker in post will give you a better SNR than an under-exposed one, and you can choose how much you want to fade for a real brightness change after the fact.

This is the right way

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reyalp

13844

Re: rawopint.lua: Fast, accurate intervalometer with raw exposure metering

« Reply #109 on: 12 / January / 2019, 16:52:00 »

Quote from: c_joerg on 12 / January / 2019, 02:51:05

Quote from: reyalp on 11 / January / 2019, 17:16:21
Making a well exposed image darker in post will give you a better SNR than an under-exposed one, and you can choose how much you want to fade for a real brightness change after the fact.
This is the right way

Being slightly pedantic, I would say it's the way with the highest potential image quality. Whether that is "right" depends on the user requirements and capability.

Slapping together a timelapse of medium res jpegs with no post processing at all is perfectly reasonable for some users, and rawopint can give pretty decent results in this case.

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