[RESOLVED] 32 bit to 16bit (2019)

[cjwidd]

Converting an approximately ~6000 x 8000 pixel image from 32-bit (.EXR) to 16-bit destroys the tonal range of the image. I understand this is a historical problem that has been addressed before, but the previous solutions are not working in this case.

Note that rendering at a lower resolution (~3000 x 4000), saving to 32-bit (.EXR), and converting to 16-bit produces a more consistent result, i.e. converting from full-float to half-float on a lower resolution image reduces the problem.

Is there a workaround for converting 32-bit to 16-bit for high resolution images?

[sprayer]

On link it's a bit different issue, did you choose this settings during converting image?

[pokoy]

Photoshop does not convert correctly when going from 32bpc to 16bpc - it just doesn't. Unless you really need to work in 32bpc in PS, it's better to save to 16 bits directly from Corona VFB or CIE.
If you really need 32bpc in PS you can use AE. You could flatten your work in PS, save as EXR and open it in AE and output to 16bpc. Make sure to setup profiles in the way you need them, so you convert to the profile you need the final image to be in. AE will work much better, PS does some black magic dark tone shifting and it's awful, there is just no way to make it work correctly in PS.

[cjwidd]

@sprayer
Yes, that's correct, I applied the HDR Toning (exposure / gamma) settings as depicted during the conversion. Unfortunately, that did not correct the issue.

I can already tell I'm going to have to submit a support ticket because I don't think I will be able to share the project files to the forum.

What's more, saving out a 16-bit image straight out of the VFB also results in tonal loss.

@pokoy
I'm willing to acknowledge that is true, but nevertheless, I need to find a workaround to bring the image that appears in Photoshop correctly in 32-bit down to 16-bit without tonal loss.

[Juraj]

What is tonal loss? You end up with gradient artifacts?

[cjwidd]

I've attached a link to a Google Drive download for a crop of the affected image.

Converting the linked image from 32-bit to 16-bit in Photoshop produces a dramatic change in the overall appearance of the image, most notably in terms of exposure / gamma correction. I cannot account for the discrepancy, but I am posting to the forum for guidance.

[sprayer]

Are you sure what you have difference in 100% zoom? Because i do not see difference after converting, only difference if you zoom out, but this i think limitation of photoshop and how it filtering big image

[cjwidd]

yeah, I was thinking that might be the case, and Photoshop just can't represent the full pixel range when the image is fit to screen, but then why is the 32-bit image fully represented before converting to 16-bit?

[James Vella]

Are you sure what you have difference in 100% zoom? Because i do not see difference after converting, only difference if you zoom out, but this i think limitation of photoshop and how it filtering big image

Agreed.

this is what I see after conversion:

[romullus]

yeah, I was thinking that might be the case, and Photoshop just can't represent the full pixel range when the image is fit to screen, but then why is the 32-bit image fully represented before converting to 16-bit?

When image is displayed at any other zoom level than 1:1, then pixels needs to be interpolated. I guess that photoshop uses different interpolation for 16 bit and 32 bit images. When comparing two images, you always need to do that at 1:1 zoom level, otherwise you can't know what are you comparing.

[cjwidd]

..then pixels needs to be interpolated.

Yes, this is exactly what I was thinking.

Well, that is an embarrassing oversight, but thank you all for clarifying 😬

I am not sure what the approach is then for photoediting, if there is so much of a difference between the 32-bit and 16-bit version when fit to screen?

[James Vella]

Yes mine looks like this when fit to screen

[cjwidd]

I suppose we are outside the purview of Corona at this point - seems like a Photoshop issue.

[cjwidd]

Would the compression (interpolation) issue appear on a high DPI monitor when fit to screen in Photoshop?

[romullus]

If the image won't fit on screen in 1:1 zoom level, then pixels will have to be interpolated no matter display resolution.