Author Topic: Difference in brightness Corona VFB vs Photoshop  (Read 4229 times)

2020-01-25, 00:41:58

lupaz

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Hi,

I'm attaching here a GIF showing the difference in brightness between the render as shown in the VFB vs in Photoshop (or regular image viewer from windows). BUT in windows "photos" there's no difference with VFB.
In the VFB it's brighter or higher exposure.

Any ideas why?
Could it be a color profile issue?

Using: Corona 5, Max 2020.3, Windows 10
Gamma in 3Ds Max is at its default of 2.2


Thanks.
« Last Edit: 2020-01-25, 01:24:23 by lupaz »

2020-01-25, 02:03:33
Reply #1

lupaz

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2020-01-28, 20:29:30
Reply #2

cjwidd

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2020-01-29, 00:37:19
Reply #3

lupaz

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In photoshop I changed the settings so it asks about color profiles whe opening them. There I choose my monitor's profile and convert to working RGB.

In my case it's a new thing bc I got a new monitor. Didn't realize it until I checked that thread

2020-01-29, 11:43:36
Reply #4

romullus

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Is this the only proper solution? I mean, it would be big annoyance to open every render in photoshop and do that assign/convert profiles hassle. I struggle with color profiles issue everytime i reinstall the OS. In the end, i manage to solve it somehow without the need of converting anything. I don't know if my solution is right or not, but as long as i get consistent picture look across different apps, i'm happy about it.
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2020-01-29, 13:57:54
Reply #5

pokoy

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Is this the only proper solution? I mean, it would be big annoyance to open every render in photoshop and do that assign/convert profiles hassle. I struggle with color profiles issue everytime i reinstall the OS. In the end, i manage to solve it somehow without the need of converting anything. I don't know if my solution is right or not, but as long as i get consistent picture look across different apps, i'm happy about it.

The problem with converting colors to a profile (instead of assigning a working RGB profile) is that your RGB values will be changed. If you need to rerender a part of the image and forgot about the profile you've chosen when converting you may have a hard time getting it to look identical. That's why I prefer to assign a profile, not convert, and I then do my post. But I do this only because I want to stick to a 100% foolproof workflow and I know what I did the last time that way. If you don't mind the pixel value change and want to have a 100% VFB match, then it can be done that way, sure.
As long as Max (or Corona VFB) isn't color managed and shows colors with a user profile it's either this or that, neither is ideal.

2020-01-29, 14:12:22
Reply #6

romullus

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The problem is, that i'm complete illiterate regarding to color management. All i want, is to have consistent image without need to assign or convert profiles. I managed to achieve this by poking in the dark with windows color profiles. As i said, i have no clue if what i did is ok or horribly wrong, but since i don't do commissioned renderings, i'm ok with that. I just have to face the fact, that i'm too dumb for this color management woodoo.
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2020-01-29, 15:31:12
Reply #7

pokoy

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The problem is, that i'm complete illiterate regarding to color management. All i want, is to have consistent image without need to assign or convert profiles. I managed to achieve this by poking in the dark with windows color profiles. As i said, i have no clue if what i did is ok or horribly wrong, but since i don't do commissioned renderings, i'm ok with that. I just have to face the fact, that i'm too dumb for this color management woodoo.

It's fairly simple, really:
- image has RGB values
- a software profile tells it how the software should display the image, this is the one that gets embedded in the file
- a display profile tells the display how to interpret and display values in general, this is done through a calibration, this one is independent from software and files

The critical part is that you have to make decisions on your own when a part of the chain doesn't care about CM. If Max/Corona applied and embedded the profile things would be easier.
Still, the most important part is neglected too often - the display. As long as it's not calibrated and has a gamut wide enough to display all the profiles reliably you can't judge colors properly, regardless of what you've done before in the chain.

2020-01-29, 17:24:13
Reply #8

lupaz

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The problem with converting colors to a profile (instead of assigning a working RGB profile) is that your RGB values will be changed. If you need to rerender a part of the image and forgot about the profile you've chosen when converting you may have a hard time getting it to look identical. That's why I prefer to assign a profile, not convert, and I then do my post. But I do this only because I want to stick to a 100% foolproof workflow and I know what I did the last time that way. If you don't mind the pixel value change and want to have a 100% VFB match, then it can be done that way, sure.
As long as Max (or Corona VFB) isn't color managed and shows colors with a user profile it's either this or that, neither is ideal.

So if your profile being used by Max is the monitor's profile, in photoshop you assign that profile (the monitor's) as your working RGB profile?

To make my workflow more graphic:

1) If I use the first option, "Leave as is (don't color manage)", the result is darker in Photoshop than in the VFB;
2) If I use "assign working RGB: sRGB", the result is also darker, identical to the above;
3) If I use "assign profile: Benq PD3200U", the result is the same as in the VFB, but I'd be working with a profile that is not a standard;
4) If I use "assign profile: Benq PD3200U" AND check "and then convert document to working RGB", what I see is the same as the VFB and I'm working with a standard profile.

Without being an expert, I'd think #4 is the best case scenario.
Is that correct?

2020-01-30, 10:47:36
Reply #9

sprayer

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This things still confusing, because color profile what goes with monitor not perfectly correct and you need to make own color profile for each monitor panel with calibration. Also i am not totally understand how installed profile affect on showing colors in apps, for example there is in all chromium base browser bug as i understand if you have custom color profile in system it take wrong color profile and in browser will be wrong colors until you forced set sRGB in browser settings
here proof https://bugs.chromium.org/p/chromium/issues/detail?id=992886#c_ts1565715865


2021-03-05, 14:19:02
Reply #10

cjwidd

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To make my workflow more graphic:

1) If I use the first option, "Leave as is (don't color manage)", the result is darker in Photoshop than in the VFB;
2) If I use "assign working RGB: sRGB", the result is also darker, identical to the above;
3) If I use "assign profile: Benq PD3200U", the result is the same as in the VFB, but I'd be working with a profile that is not a standard;
4) If I use "assign profile: Benq PD3200U" AND check "and then convert document to working RGB", what I see is the same as the VFB and I'm working with a standard profile.

Without being an expert, I'd think #4 is the best case scenario.
Is that correct?

Would really like to get some clarification on whether #4 is indeed the correct approach, or at least correct with respect to how it is being described here.

In trying to understand color management as it pertains to the Corona Renderer VFB, I'm wondering whether I am to trust the VFB image as 'accurate' if I am using the sRGB IEC61966-2.1.icm or a monitor-specific .icm (generated from an xRite i1 Display calibration device.)

Using the sRGB IEC61966-2.1.icm in the Windows device color management settings, the VFB image (.EXR) appears more washed out compared to when viewed in Photoshop.
Using the monitor-specific .cim in the Windows device color management settings, the VFB image (.EXR) appears darker / more saturated, but appears the same in the VFB and in Photoshop IFF [assign profile -> (monitor.icm) check: and then convert document to working RGB] is applied in PS.

So which is the 'true' image - the washed out VFB image (sRGB IEC61966-2.1.icm) or the darker / more saturated image (monitor-specific.icm)?

2021-03-05, 14:51:25
Reply #11

Nejc Kilar

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From my quick testing (in C4D) the Corona VFB is being affected by whatever ICC profile you are running in Windows. In PS for example you'd then need to switch from the default sRGB one to the ICC you are using in Windows too - otherwise you'll get a slightly different image.
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2021-03-05, 21:08:23
Reply #12

cjwidd

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In PS for example you'd then need to switch from the default sRGB one to the ICC you are using in Windows too - otherwise you'll get a slightly different image.

OK, this sounds more or less consistent with how I understand the issue as it's been described above. I assume then that the disparity in the image appearance in PS when NOT using the monitor .icm is due to the discrepancy in how the monitor represents sRGB (or wide gamut RGB)?

2021-03-05, 21:30:18
Reply #13

Juraj

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Photoshop doesn't run default sRGB for anything. Depending on settings it either respects the color profiles of files, ignores or assigns/converts to one. The default installation settings for Photoshop CC has been "respect when available, ignore/don't assign when not".
In terms of view transform, Photoshop reads the color profile of system (Windows, MacOS,etc..). So Photoshop always shows the correct color (if the color profile aligns with the monitor gamut).

I wrote probably 20 essays on this topic on this forum, but currently 3dsMax, and Corona, still ignore system color profile (which is mostly ICC).

Quote
4) If I use "assign profile: Benq PD3200U" AND check "and then convert document to working RGB", what I see is the same as the VFB and I'm working with a standard profile.

This is of course perfectly valid from creative standpoint, but it's wrong from color management. It only gives you identical colors between VFB and Photoshop because you essentially translated your RGB values into incorrect ones to match the incorrect result on VFB. And because both are now incorrect, they both look the same. Not sure if that is positive :- ). But I know a lot of people with wide gamut do this, it's pretty popular "hack".

To have identical and correct colors between 3dsMax/Corona VFB and Photoshop, you need to physically clamp color space (space, not profile describing one) of the Display down to sRGB. That needs to be done on hardware level, in monitor OSD menu either through factory calibrated profile (the Monitor stores 14bit 3D LUT, not ICC profile) or custom hardware calibrated profile (again, stored as 14bit 3D LUT internally in Monitor OSD, not in Windows).

BenQ PD3200U doesn't offer hardware calibration, so you are stuck with factory profile which is ok because it's pretty good.

This is correct workflow for this monitor for 3dsMax/Corona.

1) Monitor OSD Menu: Select sRGB mode. Then adjust brightness to your liking. (Fun fact: Calibration is also done to exact brightness levels, but if you move it +/- 50perc. the difference in accuracy is not drastic).
2) Type Color management into taskbar in Windows, select your monitor, check "Use my settings" and select "sRGB" ICC profile. Set "Use as default".
3) When loading any rendering into Photoshop, you don't need to do anything if your settings are set to "Don't Ask". It will stay unmanaged and you only need to "Assign" sRGB profile at the end of export, for examply when saving to final file. Don't convert to any other profile.

The above workflow doesn't work for high-gamut displaying (DCI-P3, HDR workflow,etc..) or printing (AdobeRGB, LAB,etc.). But since 3dsMax & Corona are not color managed (Autodesk Maya and Vray for example are), this is the best scenario to use right now. Least headaches. Colors are always correct, you're just not using wide-gamut capability, which is ok since most devices are sRGB only, even today.
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2021-03-05, 21:35:17
Reply #14

cjwidd

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I wrote probably 20 essays on this topic on this forum, but currently 3dsMax, and Corona, still ignore system color profile (which is mostly ICC).

Yeah I'm mostly going on your response from here