Sky Glow parameter in FilmDev

[jlh]

Hi,

It appears from the FilmDev histogram that the Sky Glow parameter basically moves the black point to the left (histogram moves to the right). If my understanding on how that parameter works is correct, would it be feasible or desirable to allow that parameter to move the black point to the right as well?

Sometimes at the end of the workflow on some images, I open FilmDev to make final adjustments. Being able to move the black point a little to the right with that parameter (allow it to go negative a few percentage points?) in order to darken the background a bit would be very helpful.

Thanks,
Jeff

[admin]

Hi Jeff,

Thank you for your post. What you appear to be suggesting would constitute data clipping/destroying (e.g. throwing away pixels below a certain threshold).
This is almost never OK, except in cases where that data can be assumed to be anomalous. For this purpose you will already find a "Dark Anomaly" filter setting in the module, as well as in the Wipe module (which is the prime candidate for ensuring your background levels are uniform and only real data is sitting on top of the moderately fluctuating "background" level).

That said, if you really must clip your data, you can coax AutoDev into doing that by choosing a Region of Interest that is brighter than the background and setting Outside RoI Influence to 0%.

I hope that helps and makes sense,

[jlh]

Hi Ivo,

Thank you for your reply and explanation. I certainly understand the goal of not clipping data in image processing. My purpose for asking about black point adjustment options was not intended to counter that goal. In processing my images (many don't have the best or cleanest data due to my city location), I am sometimes curious of the adverse impact (if any) a simple and small black point adjustment can have on the image; that is, is any (noticeable) detail loss versus improvement in background.

Some of my saved StarTools images are improved noticeably with an ever so slight black point adjustment when subsequently opened in other applications. For me it would be much more desirable if I could do that in StarTools (with the option to go back to other modules before saving) instead of needing to go to a separate processing application.

My thinking is not to undermine the general theme of not clipping data. But, if it is well documented that the Sky Glow parameter can clip data if moved, for example to a negative percent, similar to the documentation warning about clipping by other parameters, users can be careful in its use and protect their data in the best way.

Thanks again,
Jeff

P.S. For some reason by previous registration was lost and couldn't be retrieved so I had to start over with this new jlh user name

[hixx]

Hi,
Jeff's idea for black point touch up might be a potential feature for a (future) touch up module: introducing subtle dithering, e.g. using Denoise's "Grain Equalization" parameter, while adjusting black point. Thus it would apply signal theory properly, avoiding clipping.
Clear Skies,
Jochen

[jlh]

Hi Jochen,

for a future Touch Up module. From various postings I have seen I think there are others who would find it useful too.

Thanks,
Jeff