[cgbeige]

When I open rendered hdr 32-bit images in Photoshop, I get really nasty banding in low-contrast gradients that don't appear in 8-bit exports. I've tried assigning different wide-gamut colour profiles but none work (is there a default profile that these images are made for?).

Any suggestions?

[JorisMX]

Can you post some screenshots? Because I think it's not completely clear when the problem occurs...

I've had banding when exporting pngs and trying to use a strong contrast curve in PS. I've also had banding in 32 bit hdrs which basicly occured due to poor lighting and many dark lowcontrast areas.

I'm very interested in this topic as well, as I'm recently trying to resort my maxwell workflow to be more transparent.

[cgbeige]

ya, here's a pic:



the banding in the back doesn't appear in the 8-bit png, only 32-bit HDR files. Incidentally, is there a way to output 16-bit TIFFs from mxcl?

[JorisMX]

This is very weird. Any banding issues I had dealt with in the past were subtle ones in dark gradients.
Perhaps NL can tell you what the reason for this is, or rather what went wrong,
since I believe there must be some little error if you image comes out this way.

btw Elftal will win this baby

[cgbeige]

heh - I don't think you want to win the DIVA World Cup.

[Cadhorn]

I wonder if that banding is actually in the 32 bit HDR, or just the onscreen and/or downsampled JPG representation of the HDR. If you zoom in on the banding area and use the eyedropper tool and Info palette, while hovering your cursor over that area, do you see the RGB values taking big jumps? Or is it gradual?

This is not a trick question, I have no idea what the answer will be.

But, I'm thinking that if you're viewing the 32 bit HDR in photoshop, and your hardware (video card) is set to something less than 32 bit (24 or 16 bit) you would see banding on the monitor that isn't really "there" in the information stored in the file. Also, if you save the 32 bit HDR into a jpg or png or whatever, is it actually storing 32 bit info, or is it downsampling it to 24/16 or whatever? That conversion may be introducing banding.

[-Adrian]

Good point. What happens when you change to 16bit mode?

[cgbeige]

Good point. What happens when you change to 16bit mode?

it goes away. weird. so it looks like this is more of an issue with Photoshop CS4.

[cgbeige]

correction - after looking more closely, it goes away partly but there are still some bands in the image compared to the 8-bit image.

[cgbeige]

ok - I did some searching around and found what I think is a start to a fix. if you change your View settings in Photoshop to Proof Colors, it will eliminate the banding but it will still be impossible to get something close to what you see in 8-bit rendered mode. If I try and brighten the Exposure to the point where the gradient looks like it should, the rest gets blown out:



Pretty irritating. I think that the source of the problem is that Maxwell doesn't designate a destination colour space for the HDR image so it's anyone's guess how this can be fixed. If I try the EXR format for output, it's even further off.

[-Adrian]

Hmm, we've had this discussion regarding (anti)aliasing, which could be explained by the same failing mechanism. I personally render to PNG since i figured there isn't much useful i can do in 32bit mode.

[tom]

You may find this post useful
http://www.maxwellrender.com/forum/view ... 87#p275787

[cgbeige]

thanks tom but dithering is already enabled in PS and adding noise doesn't fix it.

[gotoxy av-media]

hi cgbeige,

take a look at these:

http://www.maxwellrender.com/forum/view ... =3&t=30933
http://www.maxwellrender.com/forum/view ... =3&t=30913
....and much more

to quote polynurb: i don't think there is a solution for this yet...


my solution was switching to antoher unbiased renderengine which can manage hdr properly!

munch

[cgbeige]

ya, that's not really an option for me. I love Maxwell save for this bug
Hopefully this can be addressed in 2.0