32bit Image - Adjusting Exposure Adjusts MacBook Screen Brightness?

[csscms]

Hi There, I've never edited 32bit images before so sorry if this is normal.

I have a 32bit EXR file that's been rendered in Blender (a 3D app).

If I open it, convert it to a smart object and use camera raw, adjusting the exposure also adjusts the Macbook's screen brightness - is this normal?

Because it changes the screen brightness, it looks good in camera raw but exiting displays the image overexposed...

If this is normal, how do you edit 32bit files?

**UPDATE***

Converting the PSD to 16bit doesn't adjust the Macbook's screen brightness...

Any help much appreciated.

Cheers, Ben

[csscms]

Actually, looking at the 16bit results, tone mapping before editing is much better - right?

Let me know if there's a different/better way. Cheers

[davescm]

A 32 bit/channel image is very different to 8 bit and 16 bit/channel image.

On 8 and 16 bit images the range between black and white is fixed and the image is divided into steps, the number of which depends on whether you are working in 8 or 16 bit.

However in 32 bit/channel, the image can contain values darker than the blackest black being displayed on screen and lighter than the whitest white. This is why an 'exposure slider' is provided at the bottom left of the image window (if you don't see it use the reveal arrow)  so that you choose which part of the range is shown on the limited range of your screen.  It is also why tone mapping is required when converting to an 8 or 16 bit/channel document so that you choose how the wide range of 32 bit tones are mapped into the much more limited 8/16 bit range. That includes choose whether to discard the lightest and darkest values and let them go white/black or whether to compress them.

Which is a long winded explanation, saying it all looks as expected.

Dave

[csscms]

Out of curiosity, do you know why changing 32bit image exposure, also change the Macbook's screen (hardware) brightness?

[davescm]

Are you sure it is actually changing the screen brightness? Your screenshot does not show that.

When you increase 'exposure' adjustment in a 32 bit linear image it just slides all image values to the 'right' i.e. with an extreme adjustment it moves all values out of the range being displayed on the screen, and the screen looks white. But unlike 8/16 bit images which would clip values at full white, the values are still there in the image. You can see them again if you go to the bottom left of the image window and move the 32 bit exposure slider. That slider is not actually adjusting the image at all, it merely chooses which part of the extreme range of values, available in 32 bit floating point, are displayed on the limited dynamic range of the screen.

Dave

[csscms]

@davescm It's absolutely changing the MBP's brightness - maybe it's an automated hardware sensor on the MBP?

Not only do I observe the screen brightness changing in-person (it's disconcerting) the image doesn't look over-exposed in the Camera Raw window (after the screen dims) but a screenshot of the Camera Raw window shows that the image is over-exposed.

Ive observed this with 6 different 32bit renders over the past few days now. However, I'm now tone mapping the images down to 16bit.

So at this point, I'm just curious to see if others see this bahavor and why it happens.

Cheers, Ben

[Lumigraphics]

Apple no longer sells MacBooks. You might have an old MacBook, or you more likely have a MacBook Air or MacBook Pro. Pedantics is important here because the Air and Pro models have very different screens. 14" and 16" Pro models have HDR while Air models do not. An HDR display can show a much wider range of brightness values.

[csscms]

I have a 16" M2 Max MBP. That has an HDR display - no?

[Lumigraphics]

Yes the MacBook Pro models have HDR.

[Conrad_C]

I have limited experience with it, but because I have a 14-inch MacBook Pro with an HDR-capable display and some knowledge of how it works, I thought I’d give it a try. In short, I think what you saw is not the macOS display screen brightness increasing. I think you saw the HDR image highlights becoming brighter than the SDR level you are used to, and the image highlights probably became brighter than the macOS UI white point. I also suspect that if you checked the macOS display brightness level before and after the Exposure adjustment, you would find that it was the same brightness level, it was only the image that got brighter.

Longer explanation:

I created a 32 bits per channel file by exporting an HDR-bracketed merge from Adobe Camera Raw as a 32bpc HDR TIFF file, and opened that it in Photoshop. I also made sure Photoshop was configured for HDR display by opening Photoshop > Settings (Preferences), clicking Technology Previews, and making sure Precise Color Management for HDR Display is enabled. This option was added relatively recently.

I had a suspicion that the real difference would be easiest to see if I had the same image on my HDR (MacBook Pro) display and my normal old non-HDR desktop display, so I chose Window > Arrange > New Window For [document name] (to make a second window for the same document) and moved the second document window to my non-HDR display.

With that all set up, I started increasing the Exposure value for the 32bpc HDR image, and what I saw was exactly what I expected:

On the MacBook Pro HDR display: Yes, the image became very bright, much brighter than usual, retaining the highlight detail that you would expect in an image that’s taking full advantage of HDR editing on an HDR display. All as expected.

On the old, common SDR display: The same image became brighter, but the highlights got clipped and blown out as soon as they hit the maximum brightness level of the SDR display. Also all as expected; the SDR display cannot reach the same brightness level as the HDR display.

Now I’ll address the question about the MacBook Pro brightness “being adjusted.” No, I did not observe that at all. The overall macOS display brightness setting did not change. What I did observe is something that looks a lot like that, but is actually not the same thing: The image highlights became exceptionally bright, brighter than the macOS UI, brighter than the menu bar for example. For an HDR-capable display, this is normal. But not expected if someone has only worked with SDR displays.

Most displays, like my common old SDR display, may reach 250–500 nits of brightness. The HDR-capable MacBook Pro display is rated for up to 1000 nits for normal viewing. This is how bright the UI can get. When viewing HDR content, the display can reach 1600 nits for the brightest highlights. When you increase Exposure far enough, you can push the image beyond the UI white point, so you find that the image appears super bright, because it’s brighter than you’ve ever seen it on a non-HDR display. But if you pay close attention to the UI whites, they are probably not increasing as you adjust exposure, and also, you may find that UI white is darker than the highlights in the image. This is why I’ll say that what you are seeing is the image highlights going into the HDR highlight range, but the overall macOS display brightness is not changing.

I think you’ll also observe that if you check your macOS display brightness level before and after adjusting Exposure. It’s probably at the same level before and after — not affected by Exposure in Photoshop, which should affect only the image.

Also, all of the above is true only if, in macOS System Settings > Displays, the currently selected macOS Reference Mode Preset supports HDR. If the Preset is at the default setting, Apple XDR Display (P3-1600 nits), then that is the full range HDR preset and will display the way I described, with image highlights possibly exceeding UI SDR white while holding highlight detail properly. If you selected one of the Reference Mode presets that does not support HDR, such as Photography (P3-D65), then it will behave like an SDR display and the image will not become brighter than the macOS UI (but you won’t get to see HDR highlight detail).

If my understanding is correct, I have to say I didn’t learn about it from reading about Photoshop, I learned about it from the HDR display explanations in the Adobe tech article linked below, about the relatively new full range HDR editing feature in Adobe Camera Raw and Adobe Lightroom Classic:

High Dynamic Range Explained

[Conrad_C]

**UPDATE***

Converting the PSD to 16bit doesn't adjust the Macbook's screen brightness...

By @csscms

This is because editing as full range HDR requires 32 bits per channel mode.

If an HDR image is converted to 8 or 16 bits per channel, the full HDR highlight range is not supported, and tone mapping is needed to compress highlight detail down into a range that 8 or 16bpc can handle. The advantage of editing at 8 or 16 bpc is that you can easily see how it’s going to look on non-HDR displays…but by exiting 32 bpc, you’ve lost the HDR highlight levels so hopefully they were tone-mapped down into SDR before the conversion out of 32bpc.

(And again, I don’t think the display brightness was changing, based on my other reply.)

[csscms]

@Conrad_C Thanks for taking the time to post, a couple of things I don't understand (if you have time).

Settings Changes

• I've now enabled: Photoshop Settings > Technology Previews > Precise Color Management for HDR Display
• I've also disabled: MacOS Settings > Displays > Automatically adjust brightness

1.

When I adjust the brightness of the 32bit EXR in the Camera Raw Filter, it's definitely brighter on the eyes (I initally have to sqint a bit) and the highlights are overblown. But over about 1-2 seconds, the highlights adjust and highlight detail comes back. The way the screen adjusts over 1-2 seconds is what made me think hardware adjustment was invloved. But if this is normal, then all good! It's my first time.

2.

When I click OK to exit the Camera Raw filter, the image in the main PS window is overblown and looks nothing like the Camera Raw filter. Here's another image so you can see. How do I get the image to display correctly in the main PS window? It's 32 bit...

It's like the Camera Raw Filter is HDR but the main Photoshop window is not?  Or am I missing something basic again? Or are 32bit smart objects not supported?

I'm now tone mapping to 16bit but just wanted to understand what's going on here as 32bit is new for me.

I hope that make sense. Cheers, Ben

[Conrad_C]

I just tried out your steps, and I think I might see what you’re seeing. I did notice a few differences in your steps that isn’t something I’ve tried before.

(I’m still using a 32bpc TIFF because I don’t have a 32bpc EXR file, but it seems to work the same way. Also, I’ll assume that when you open Camera Raw Filter for the 32bpc image, in Camera Raw, HDR is enabled, because that will allow very high brightness.)

When I adjust the brightness of the 32bit EXR in the Camera Raw Filter, it's definitely brighter on the eyes (I initally have to sqint a bit) and the highlights are overblown. But over about 1-2 seconds, the highlights adjust and highlight detail comes back. The way the screen adjusts over 1-2 seconds is what made me think hardware adjustment was invloved. But if this is normal, then all good! It's my first time.

By @csscms

I think I saw a transition the first time I exited Camera Raw, but it seemed to be only the first time., and it was less than one second. If things are set up properly, even if there is a transition, the end result in Photoshop should look exactly the same as it did in Camera Raw Filter, no brighter or darker.

If yours is too light after exiting Camera Raw, I did just think of one thing to look at. Choose View > 32-bit Preview Options, and make sure Exposure is 0 and Gamma is 1.00 (in other words, make sure they are not altering the display). These options go back many years as a blunt workaround for trying to view HDR images on non-HDR displays. But now that we are using high quality full range HDR displays like the Apple XDR on the 14/16" MacBook Pro, I have a suspicion that 32-bit Preview Options should not be altered or touched on a real HDR display.

Also, the next time you see it, watch other things on the screen carefully, not just the image but also the lighter parts of the UI such as the menu bar and text in the document tab. Because if HDR adjustments are made that brighten highlights beyond SDR, what’s expected is that even if you see the image get brighter, the UI should stay the same. In other words:

• If the entire screen is changing, from corner to corner, including UI, then that is a display brightness setting change. 
• If only the canvas area gets brighter, but you see the Mac and Photoshop UI stay the same brightness, then that is not a change in the macOS display brightness setting. This is what should be happening, the image can use the upper end of the HDR brightness range (and the UI will not). Another way to tell if this is happening is if the brightest highlights are brighter than 100% white in SDR windows; for example, I put a blank (100% white) 32bpc Photoshop document side by side with a blank (full white) Microsoft Word document, and as I increased Exposure in Photoshop, the level of 100% white in Photoshop exceeded 100% white in the Word document background.

I also figured out a way to simplify the explanation with a demonstration. Try this:

1. Set the Photoshop Color Theme to Light. (Preferences, Interface). This is optional, but it makes the effect easier to see. 

2. Create an empty Photoshop document with nothing but a solid white Background layer, and make sure Mode is set to 32 bits/channel. 

3. Add an Exposure adjustment layer (Layer > New Adjustment Layer > Exposure), or apply Camera Raw filter with HDR enabled. 
4. Increase Exposure to at least +2. (If in Camera Raw Filter, click OK to apply the change to the Photoshop document.) You will see the document white become very bright, but…the rest of the screen does not get any brighter. This is the clue that it is not an overall screen brightness adjustment, only an adjustment to the tonal values of the open document only. 

What you see in step 4 happens only if:

• The document is set to 32 bits/channel. 
• The Reference Mode preset in macOS Displays supports HDR content, such as the built-in preset Apple XDR Display (P3-1600 nits). 
• (I’m not sure, but it might also be necessary for Precise Color Management for HDR Display to be enabled, I know you did enable that.)  

When the above are not true, then no matter how high you push Exposure, Photoshop document white cannot exceed maximum white in other SDR documents or white parts of the UI.