ZBrushCentral

incorrect Grey scale values

I have found that when the mid level is set to 50 in Z brush so that 128,128,128 grey is Zero displacement, Z brush is actually outputing 149,149,149 as Zero displacement, which is causeing bloating in the displacement renders.

THis became apparant to me while using Mental Ray and setting the alpha offset to half of the alpha gain, so the AG 1 = AO -.5 which is correct for getting the proper displacement from the textures from Zbrush . I corrected this by taking the dis map into photoshop and lowering the brightness value until the nuetral grey area read as 128,128,128 then the Mental ray render was correct.

I tested it several times and Z brush always sets the nuetral displacement value to 149,149,149 which is incorrect is there something that I have set wrong, I thought that if you set the Mid level in the displacement options to 50 that you would get 128 for grey which is the middle of 0 - 255

has anyone else noticed this??

on a side note what I do to determine if my displacement settigs are correct is imoport the high res mesh from Z brush into Maya (yeah kinda slow but worth it) for reference then I put my low cage object directly behind it with an ambient red shader on it, so when I render from the side ortho view I can see if the red displaced mesh is sticking out further than the high res mesh in front of it.leg example01.jpg

another test to illustrate this is to make a Plus with Z add and a minus sign with Z sub in projection mode so you have equal displacement, export the dis map and check the middle grey area and you will see that its at 149 149 149,

( in this image if you sample the corrected 128 area it will actually read as 129 due to the Jpeg compression :slight_smile:

again all im doing to get the correct level is lowering the images brightness value in photoshop by -23 to go from 149 to 128 for the mid grey range, this shouldnt mess up the image but if someone knows a more accurate way to do this please let me know. Thanks!plus.jpg

ZBrush is producing the correct mid-gray values. It is Photoshop’s color management which is readjusting the mid value. Make sure to turn off color management in Photoshop when working with displacement maps.

so why does mental ray produce a bloated model then when displaced, my settings where 1.8 alpha gain and -.9 for alpha offset and it was bloated until I adjusted it in photoshop?? what am I missing? Im pretty sure that if I just load a texture into photoshop and save it as a different formatt that photoshop isnt messing with grey levels in such a simple process, if it is then photoshop should be strung up!!! hehe

thanks for you help, any further info would be appreciated as I feel I still dont understand how photoshop is altering the image.
thanks-Kris

holy crap!!! I turned off colormangment and low and behold its now correct, I had no idea that photoshope was doing this, wow, well I hope other see this as well I have been using photoshop for 10 years and I had no clue,

thanks again for you help!!! I was begining to think I was crazy!