Participant

Question

32bit levels not working - how to set black point and white point

Forum|Forum|2 years ago
April 15, 2023
2 replies
3396 views

Anyone know how to get levels to work in 32bit images.

Currently if I open a 32 bit HDR exr image and then go to levels (image>adjustments) to set the black point and white points it doesn't work.

Further, it shows 0-255 and I think that the range of the image should have significantly more range, so it seems like a bug - it's actually treating it like an image with lower bit depth.

I am aware that my monitor doesn't have the full range, I'm prepping an image to use as an HDRI for 3d render. I am also aware that since I don't have a "true" 32 bit white and black point that I am remapping onto the 32bit full range. I guess that is the point of the levels adjustment though. Or is levels broken for 32bit? Not sure if this is bug but definitely does not seem to be expected operation.

Thanks!

vers Photoshop 24.2.0

Mac Ventura 13.2

This topic has been closed for replies.

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virtualhc

Participant

The way I've done it when producing HDRI images for 3D ligthting is to select the sun disc and then use the Exposure adjustment whcih is the only tool that I've foind in Phtoshop that would allow you to push the pixel brightness beyond the SDR range and as high as you want within the 32 bit range. On the other hand, I just came accross your post looking for a way of expanding the higher range of the whole sky, and masking it between tree leaves is not easy, particularly when several of the automatized selection tools in Photoshop simply don't work in 32 bits mode (e.g., the magic wand). I was looking for how I could use the Curves or other Image Adjustment tools to push the highlights beyond the SDR limit but from what I see in this thread it seems it's not really possible. I'll look into Affinity Photo or the other suggested editors. Have you found any good alternatives since you posted this?

kelvinproblem

Participating Frequently

Hi There,

Honestly I found some success using PhotoLine as @Wim5F94 suggested. It includes the referenced adjustment layer that allows manipulation of 32bit image data. That said, I only just got it to work for my use-case and I didn't feel like the method was very fluent. Also, I got excellent feedback from the people who wrote the program and they seemed to recognize this was a hole in adobe's support for an important image type. I recommend you give it a try.

Why adobe has levels for 32bit images but constrains it to 8bit range still bewilders me. Many, many people use HDRI images to illuminate 3d scenes and assets but adobe has basically said that this is a no-go as far as I can see.

I'd appreciate it in turn if you could post any successful directions you find. Good luck.

davescm

Community Expert

Levels does not allow you to map onto the entire 32 bit range it just maps within the range of the image.

You can map your image levels onto whichever part of the 32 bit range you choose using Exposure which offers a linear exposure adjustment along with offset and gamma.

As an aside I always prefer adjustment layers, rather than image>adjustments, as adjustment layers remain editable

Dave

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helpwHDRAuthor

Participant

Hi Dave,

Thanks for your response here. It sounds as though you are saying it is not a bug, which is helpful.

But the histogram that levels provides at least shows info about what is in an image from the full dynamic range, right? That is the point of the histogram, isn't it? I guess I don't understand what you say here: "Levels does not allow you to map onto the entire 32 bit range it just maps within the range of the image." What does "maps within the range of the image" mean if not from the full dynamic range? I should say I do always work with adjustment layers.

I tried exposure as you said and it does provide the eyedroppers for black and white point but honestly I couldn't get it to work as you describe. If I, say, click on the sun as absolute white point with the white point dropper it does not seem to effect the full HDR range when I slide the 32-bit exposure to see what information is at the top and bottom of that range.

Can you give a bit more info about how to map the various parts of the 32 bit range as you say?

Though I should say, I only want to spec black points and white points at the end of that 32 bit range. And I don't want to judge as such, just spread it out, this is a frame from an HDR video and I plan on automating the full image sequence.

davescm

Community Expert

An attempt to map 255 8 bit integer (or 65536 16 bit integer levels) onto the full range of 32 bit floating point makes no sense. 8 bit and 16 bit integer images divide a fixed white and black point into 256 or 65536 levels.

32 bit linear images use floating point numbers and have a massive dynamic range from theoretical black to thoretical eye burning brightness (a range which cannot appear on a monitor). Spreading an existing image across such a wide range would just result in massive steps between each level and hence the tools are not provided to attempt that.

So the way HDR is handled is to take several exposures and map them 'next' to each other in that range so that the range is extended compared to a single capture. However, doing that you will not reach the limit of 32 bit floating point numbers even ignoring the theoretical infinity and using the max value of +/- 3.40282346639e+38

Dave

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