Yet Another Sunset Script (yass) v4.5 - page 10 - LUA Scripting - CHDK Forum
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Yet Another Sunset Script (yass) v4.5

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Offline oneaty

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #90 on: 01 / November / 2014, 17:29:02 »
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ok, thanks.
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Offline oneaty

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #91 on: 04 / November / 2014, 12:03:29 »
My late yass4 sunrise time lapse presents a sudden change of brightness in the middle of the image sequence.

I have already taken other sunrises and this is the first time it happens.

The only difference I can think of is the fact that I used Canon's AFL for the first time according to the following steps:

1. Aimed camera at distant buildings, half-pressed the shutter and simultaneously pressed the left key to get AFL;
2. Aimed camera to a higher angle to get the scene filled with sky;
3. Started yass4

What I'm thinking about is that maybe I also have locked some wrong initial exposure settings when I aimed the camera down below. (Although the images before the brightness change seem ok to me)

If needed, this link shows the image sequence at the exact point where the brightness made a big leap: http://s808.photobucket.com/user/glapido/library/20141104-yass4/04?sort=2&page=6

Attached follows csv log file

UPDATE: The sudden brightness change occurs between IMG_9745.JPG and IMG_9746.JPG
« Last Edit: 04 / November / 2014, 12:50:43 by oneaty »
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Offline waterwingz

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #92 on: 04 / November / 2014, 19:07:42 »
Quote from: oneaty on 04 / November / 2014, 12:03:29
My late yass4 sunrise time lapse presents a sudden change of brightness in the middle of the image sequence.

The only difference I can think of is the fact that I used Canon's AFL for the first time according to the following steps:
What I'm thinking about is that maybe I also have locked some wrong initial exposure settings when I aimed the camera down below. (Although the images before the brightness change seem ok to me)
Thanks for attaching a log file and links to actual images.  That helps a lot.

What you are seeing here has nothing to do with the fact that you used AFL. That only sets the focus and locks it in place. It has no effect on exposure.

Instead, you are seeing the combination of two effects.   Prior to shot IMG_9745.JPG,  the script is tracking the sunrise as the brightness increases but is slightly behind the true exposure setting  (so the images are slightly over exposed).   When the shutter speed hit the Tv normal limit you specified in the script parameters ( Tv = 1/4 sec ) the script disables filtering and the shutter speed immediately jumps to correct value, resulting in the exposure jump you see.

As far as I know,  the logic behind the use of "Tv normal limit" was based on using the script for sunsets rather than sunrises.  You might simply want to disable it by setting it to a really high value.
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Offline oneaty

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #93 on: 05 / November / 2014, 03:52:29 »
Now I see why prior sunrises I did worked: I almost certainly started shooting them when Tv was already above Tv Normal Limit. (I wasn't logging at that time, but I remember that I tried but I never could start in pure darkness - not easy to wake up so early...)

I will try disabling it as you suggested.

I'm curious, what do you mean by "filtering"?

Anyway, thanks a lot!!
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Offline waterwingz

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #94 on: 05 / November / 2014, 08:42:10 »
Quote from: oneaty on 05 / November / 2014, 03:52:29
I'm curious, what do you mean by "filtering"?
It's an electronic signal processing term.  Technically, the script is doing a low pass filter :
http://en.wikipedia.org/wiki/Low-pass_filter
but an easy way to think about it is that is just averages many exposure readings so that that you don't see as rapid changes - only the average over a period of time.
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Offline oneaty

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #95 on: 05 / November / 2014, 16:02:02 »
Quote from: waterwingz on 04 / November / 2014, 19:07:42

When the shutter speed hit the Tv normal limit you specified in the script parameters ( Tv = 1/4 sec ) the script disables filtering and the shutter speed immediately jumps to correct value, resulting in the exposure jump you see.

Sorry returning to this, but Isn't it the opposite?

Shouldn't this read like "when the shutter speed hit the Tv normal limit the script enables filtering..."?

If I correctly understood it, since it was a sunrise event, the camera started at Tv low limit, and while it didn't reached Tv normal limit, it was using exposure ramp adjustment mode.

When it hit Tv normal limit, it started using filtering mode.

And that's when the exposure jump occured.

But isn't filtering supposed to average the speed change with the previous speed value?
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Offline oneaty

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #96 on: 05 / November / 2014, 16:42:55 »
Another thing that occurred to me is that this is the first sunrise with v1.3.

Before that, with v1.2, a couple of sunrises showed no exposure jumps, and they were all executed with the same settings as this one.
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Offline waterwingz

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #97 on: 05 / November / 2014, 18:50:22 »
Quote from: oneaty on 05 / November / 2014, 16:02:02
Sorry returning to this, but Isn't it the opposite? Shouldn't this read like "when the shutter speed hit the Tv normal limit the script enables filtering..."?  If I correctly understood it, since it was a sunrise event, the camera started at Tv low limit, and while it didn't reached Tv normal limit, it was using exposure ramp adjustment mode. When it hit Tv normal limit, it started using filtering mode.
Sort of.  We are getting caught up in using inexact terminology here.  The "ramp adjustment mode" is just another filtering technique and that's what I was referrring to.  Above the "Tv normal limit" it no longer uses the ramp filter method but switches to the averaging the current exposure reading with the previous one.  Also a filter method.

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And that's when the exposure jump occured.
Correct.  As the sun was rising,  the light level was increasing quickly.  The ramp filter was not keeping up and when the script switched to the averaging filter,  there was a noticeable jump.

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But isn't filtering supposed to average the speed change with the previous speed value?
I think the issue here is that what works pretty well for sunsets does not work as well for sunrises.

Quote from: oneaty on 05 / November / 2014, 16:42:55
Another thing that occurred to me is that this is the first sunrise with v1.3.  Before that, with v1.2, a couple of sunrises showed no exposure jumps, and they were all executed with the same settings as this one.
Always interesting to know if something else has changed - thanks for mentioning that.  However, in this case it has nothing to do with what you are seeing.
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Offline oneaty

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #98 on: 11 / November / 2014, 05:49:23 »
Quote from: waterwingz on 04 / November / 2014, 19:07:42
You might simply want to disable it by setting it to a really high value.

Do you mean hard coding a very high normal speed value (like 1/3200) directly into the script, or just using the highest value in the parameter available range (which is 1/15 if I'm not wrong)?
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Offline waterwingz

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Re: Yet Another Sunset Script (yass) v4.5
« Reply #99 on: 11 / November / 2014, 07:40:44 »
Quote from: oneaty on 11 / November / 2014, 05:49:23
Do you mean hard coding a very high normal speed value (like 1/3200) directly into the script
Yes, I meant a high normal speed value  (like 1/3200 or even 1/6400). 
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, or just using the highest value in the parameter available range (which is 1/15 if I'm not wrong)?
But as you noticed, you can't do that with the values available in the script parameters for the Tv normal limit. 

However, you can (as you suggested) hard code it by changing line 73 from :

Code: [Select]
    tv_normal_limit = tv_ref[e+16] to

Code: [Select]
    tv_normal_limit = 576
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