POV-Ray : Newsgroups : povray.binaries.images : city buildings-- WIP 2 Server Time
29 Mar 2024 07:14:46 EDT (-0400)
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From: Alain
Subject: Re: city buildings-- WIP 2
Date: 5 Aug 2017 13:27:33
Message: <59860005@news.povray.org>

> I just noticed something strange about the PNG images I posted: When I look at
> the small *preview* images here in my post (using the latest version of
> Firefox), they look correct: identical to how they appear on my own machine,
> when viewed in either Photoshop or the Windows Photo Viewer. (BTW, I
> post-processed the images in PS, but only to combine two renders into one post.)
> 
> But when I click on the image previews here-- and the higher-resolution versions
> appear-- the gamma of the images isn't correct! They look darker, with more
> contrast.
> 
> Does anyone else notice this? Right now, I have no idea what's going on, or why
> they appear differently on the same website.
> 
> Honestly, I simply don't trust PNG images to show up consistently or correctly,
> anywhere! :-(  I should have posted them as jpegs.
> 
> 
> 
PNG contain gamma information, JPEG don't.
The problem is not the PNG, it's the application used to display them 
that is to blame. Some correctly use the png's gamma chunk and display 
it corrrectly no mather the actual gamma of the device used, other just 
don't.
JPEG don't have any gamma chunk, whitch makes gamma adjustment 
impossible. So, the display becomes dependent on the gamma setting of 
the device used to display it. If that device have the same gamma as 
that of the author, all is fine, otherwise, the image get to dark or to 
light and washed out.
Typically, a JPEG image made on a PC will look washed out on am Mac, and 
one made on a Mac will look to dark on a PC.
When using PNG, it should not be the case. The image should display the 
same on both platforms.


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From: Alain
Subject: Re: city buildings-- WIP 2
Date: 5 Aug 2017 13:31:19
Message: <598600e7@news.povray.org>

> 
> One more image test, again for my own purposes: This PNG is *directly* from
> POV-Ray (and NOT post-processed in Photoshop.) If it shows up correctly here
> both as a small preview AND as the larger hi-rez image, then the problem will be
> in my use of Photoshop, for some strange reason. An interesting experiment...
> 

It looks like photoshop is messing up the gamma chunk in some way. Maybe 
it plugs in the actual gamma setting of your system when it need to keep 
the original one.


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From: Kenneth
Subject: Re: city buildings-- WIP 2
Date: 5 Aug 2017 15:30:01
Message: <web.59861c4454c85aac883fb31c0@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:
> On 5-8-2017 4:44, Kenneth wrote:
> >
> > One more image test, again for my own purposes: This PNG is *directly* from
> > POV-Ray (and NOT post-processed in Photoshop.)
>
> Yes, this is much better indeed, although the original ones posted were
> awesome already. But, not knowing the problem, it was difficult to judge.
>
> Excellent work, Kenneth!
>

Thanks, Thomas!

If I seem preoccupied with this image/gamma business, it's because I'm *finally*
close to solving a PNG problem that has been dogging me for years-- specifically
concerning POV-Ray (v3.7xx) PNG renders being post-processed in my (older)
version of Photoshop.

But the newsgroup's PREVIEWS are a different problem. I've attached a screenshot
comparison of my first image post: the visual difference between the newsgroup's
SMALL image preview vs. the larger hi-rez preview-- just to prove that I'm not
imagining it ;-)  (I resized both screenshots to make the comparison easier.)
WHY they should be different is a mystery, above and beyond whatever gamma
mistake I might have made in Photoshop. The two versions should look identical.

I also downloaded my own original PNG image post (the one shown in these
screenshots), and it appears correct in *all* of my various image-viewer apps,
no gamma change.


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Attachments:
Download 'preview_comparison.jpg' (455 KB)

Preview of image 'preview_comparison.jpg'
preview_comparison.jpg


 

From: Kenneth
Subject: Re: city buildings-- WIP 2
Date: 5 Aug 2017 16:15:01
Message: <web.5986268c54c85aac883fb31c0@news.povray.org>
Another test-image post-- hopefully my final gamma test... ;-)

This PNG render is post-processed in Photoshop, but I CHANGED my usual 2.2 gamma
there (in PS) to 1.0. *IF* this image shows up correctly here-- in both small
and large previews-- then I will at least have solved the major part of my *own*
problem...

[The thing is, the image looks WRONG in Photoshop with a gamma of 1.0 there--
it's washed out, as I would expect-- but I'll let that pass for now.]

** keeping my fingers crossed **


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Attachments:
Download 'ps_gamma_1_test.png' (1786 KB)

Preview of image 'ps_gamma_1_test.png'
ps_gamma_1_test.png


 

From: Kenneth
Subject: Re: city buildings-- WIP 2
Date: 5 Aug 2017 17:30:01
Message: <web.5986384754c85aac883fb31c0@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
> Another test-image post-- hopefully my final gamma test... ;-)
>
> This PNG render is post-processed in Photoshop, but I CHANGED my usual 2.2 gamma
> there (in PS) to 1.0. *IF* this image shows up correctly here-- in both small
> and large previews-- then I will at least have solved the major part of my *own*
> problem...
>

Success!! Both preview sizes here look identical, and correct--well, with maybe
a *very slight* washed-out appearance in both-- but that could be from a number
of reasons on my end, and is unimportant in the bigger scheme of things ;-)

SO... it seems that my use of Photoshop-- at its *typical* gamma setting of
2.2-- was introducing a gamma change into the POV-Ray PNG image. I have aways
assumed 2.2 to be the correct gamma in PS, for any/all PNG images that I've
downloaded from the 'net, and even for Photoshop-created PNG images. But it's
NOT correct for post-processing a POV-Ray PNG render: a PS gamma of 1.0 is
necessary (at least for both of the newsgroup's two preview sizes to show up
correctly!) So, *something* is amiss somewhere-- either a flaw in my version of
Photoshop, OR in how the newsgroups treat preview images.

By the way, these are my POV-Ray render settings:
A) assumed_gamma 1.0 in the scene file
B) Display_Gamma of 'srgb' in my .ini file
C) File_Gamma of 'srgb' in my .ini file


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From: Kenneth
Subject: Re: city buildings-- WIP 2
Date: 5 Aug 2017 18:20:01
Message: <web.5986436754c85aac883fb31c0@news.povray.org>
"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> "Kenneth" <kdw### [at] gmailcom> wrote:
> > With a little bit of fog thrown in-- smog, or city pollution.
>
> This is a nice project, looking good. What happens if the fog is too dense to
> see the ground? :)

Answer: Too much fog! ;-) I spent hours trying to get a combination of regular
and groud fog that looked reasonably correct-- but it's still not right. (I may
do away with it altogether; some New York City aerial photos I've seen are
crystal clear, all the way to the horizon!)
>
> You could also try to group buildings in blocks, alley-distance apart, with
> blocks separated more widely. Maybe vary the height distribution using a
> large-scale pigment to select the maxima - you tend to get clusters of tall
> buildings in many cities.
>
I hadn't thought of that-- and you're absolutely right. For example, Manhattan
definitely has various-size cluters, mainly because of the depth of bedrock in
various parts of the city. Some areas just can't sustain the heavier loads, even
with pilings. That's a detail for my own city that I completely neglected-- and
it would add to the realism. Thanks!


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From: Ive
Subject: Re: city buildings-- WIP 2
Date: 5 Aug 2017 18:35:22
Message: <5986482a$1@news.povray.org>
Am 8/5/2017 um 23:27 schrieb Kenneth:
> "Kenneth" <kdw### [at] gmailcom> wrote:
>> Another test-image post-- hopefully my final gamma test... ;-)
>>
>> This PNG render is post-processed in Photoshop, but I CHANGED my usual 2.2 gamma
>> there (in PS) to 1.0. *IF* this image shows up correctly here-- in both small
>> and large previews-- then I will at least have solved the major part of my *own*
>> problem...
>>

actually this PNG image has a embedded gamma of 2.0 and the image you 
did post earlier (the dark one) has a gamma chunk of 4.4 - and this 
doesn't make any sense at all.
>
> Success!! Both preview sizes here look identical, and correct--well, with maybe
> a *very slight* washed-out appearance in both-- but that could be from a number
> of reasons on my end, and is unimportant in the bigger scheme of things ;-)
>
> SO... it seems that my use of Photoshop-- at its *typical* gamma setting of
> 2.2-- was introducing a gamma change into the POV-Ray PNG image. I have aways
> assumed 2.2 to be the correct gamma in PS, for any/all PNG images that I've
> downloaded from the 'net, and even for Photoshop-created PNG images. But it's
> NOT correct for post-processing a POV-Ray PNG render: a PS gamma of 1.0 is
> necessary (at least for both of the newsgroup's two preview sizes to show up
> correctly!) So, *something* is amiss somewhere-- either a flaw in my version of
> Photoshop, OR in how the newsgroups treat preview images.
>

Which PS version do you use? Adobe changed the handling of various image 
file format between different versions a lot and especially Photoshop's 
handling of PNG in anything older than CS6 is known to be flawed.

I usually do recommend to open images in PS that do not include an ICC 
profile in a way that that PS does NOT assign a "working colorspace"
and also does NOT assign a color profile.

-Ive


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From: Kenneth
Subject: Re: city buildings-- WIP 2
Date: 5 Aug 2017 20:20:01
Message: <web.59865f6154c85aac883fb31c0@news.povray.org>
Ive <ive### [at] lilysoftorg> wrote:
> Am 8/5/2017 um 23:27 schrieb Kenneth:
> >
> > Another test-image post-- hopefully my final gamma test... ;-)

>
> actually this PNG image has a embedded gamma of 2.0 and the image you
> did post earlier (the dark one) has a gamma chunk of 4.4 - and this
> doesn't make any sense at all.

WOW, that's... crazy. I don't even know what to make of it. *Thanks* for
checking this out. One idea that occurs to me (which could be wrong, of course)
is that posting a PNG to the newsgroups changes the gamma... perhaps twice, for
the two different-sized previews. ?? Otherwise, it's a mysterious problem with
several interrelated causes, my Photoshop being only one of them.

If you don't mind doing so, would you check the gamma chunk in the 'raw' POV-Ray
PNG image I posted, the one that begins with this:
"One more image test, again for my own purposes: This PNG is *directly* from
POV-Ray (and NOT post-processed in Photoshop.)..."

I'm curious to know what *that* turns out to be.
>
> Which PS version do you use? Adobe changed the handling of various image
> file format between different versions a lot and especially Photoshop's
> handling of PNG in anything older than CS6 is known to be flawed.
>

Version 5.0, I'm embarassed to say. And yes, I also read somewhere that such
'older' versions had some kind of flaw in their handling of PNGs... although I
don't know the technicalities.


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From: Kenneth
Subject: Re: city buildings-- WIP 2
Date: 6 Aug 2017 06:40:00
Message: <web.5986f04454c85aac883fb31c0@news.povray.org>
"BayashiPascal" <Pas### [at] BayashiInJapannet> wrote:
> That's really nice.
> I think you should also make different photos for the 1st floor of the
> buildings. At least to give them an entrance.

YES, I've been thinking the same; it's on my to-do list now. A ground
floor/lobby would add a LOT to the look of the rather boring facades. I'm not
yet sure how I'm going to go about it, though-- with (more) photos, or maybe
with some kind of fancy procedural pigment instead, that has some randomness to
it.

> Do you plan to add people, vehicles and traffic signs in the street ? It looks
> like an endless project ! :-)

I'm thinking of adding some moving cars at least-- as soon as I get around to
making some ;-) Yeah, this city project has taken on a life of its own. But I
discover some new techniques every time I add or change something, so it
continues to be a nicely challenging coding exercise.


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From: Ive
Subject: Re: city buildings-- WIP 2
Date: 6 Aug 2017 06:40:26
Message: <5986f21a$1@news.povray.org>
> WOW, that's... crazy. I don't even know what to make of it. *Thanks* for
> checking this out. One idea that occurs to me (which could be wrong, of course)
> is that posting a PNG to the newsgroups changes the gamma... perhaps twice, for
> the two different-sized previews. ?? Otherwise, it's a mysterious problem with
> several interrelated causes, my Photoshop being only one of them.
>

There *is* a problem with the web interface as the code that creates the 
downsampled preview always assumes an input image with 2.2 (or sRGB) 
gamma. It takes the original image data, resamples it and does tag the 
output as sRGB regardless of the original gamma information.
On the other hand, how the image itself appears solely depends on the 
way the browser handles it. And luckily we live in 2017, 10 years (or 
so) ago literally EVERY browser did handle it differently.
And BTW the problem is not limited to PNG images, it would also happen 
when you use for instance a JPEG with an ICC profile stating a non 2.2 
gamma.


> If you don't mind doing so, would you check the gamma chunk in the 'raw' POV-Ray
> PNG image I posted, the one that begins with this:
> "One more image test, again for my own purposes: This PNG is *directly* from
> POV-Ray (and NOT post-processed in Photoshop.)..."
>
> I'm curious to know what *that* turns out to be.

As expected - this one has a sRGB chunk.
(Rendered with POV-Ray 3.7.1-beta.9 at 22:22, 2017-08-04)


> Version 5.0, I'm embarassed to say. And yes, I also read somewhere that such
> 'older' versions had some kind of flaw in their handling of PNGs... although I
> don't know the technicalities.
>

I've worked with all versions of Photoshop before they turned to CC and 
Adobe's handling of some image file formats was always a mess. But for 
PNG it was the worst of all as Adobe did - when switching versions -  do 
it wrong again, but in a different way. So e.g. a PNG file written with 
PS 5.0 will look unexpected different when opened in CS1.
Good news is, as a user you can work around these issues. But as I've 
used version 5.0 quite a long time ago (20 years ?) I cannot tell 
anymore how the settings are called and where to find them.
Look somewhere at Preferences->Settings->Color management. There should 
be somewhere a checkbox saying something like "always ask when profile 
differs" and make sure it is checked. When opening now e.g. a PNG file 
written by POV-Ray a dialog should pop up asking you if you would like 
to apply a color transform and you should say NO.
But as mentioned, I'm not entirely sure, maybe this was the way v6.0 did 
handle it.

-Ive


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