Questions about Gamma/LWF - Max to PS

[debendraroy]

Hi all,

 

I've read a few blog posts about gamma & I believe I have an idea about what it is & its importance. Yet I'm confused about certain things.

 

Let's say I set everything in Max (2012 witth mental ray) to 2.2 (everything ticked & both bitmap input & output set to 2.2). What I want to be able to do is correctly post-process the image in Photoshop.

 

1. What format should I save the final image in Max if I have to get the most out of post-processing in Photoshop - exr, tif? 16 bit or 32 bit?

 

2. By setting the bitmap output to 2.2, I'm essentially burning gamma in, right? If I choose not to burn it in, how do I work with it or correct it in Photshop?

 

3. Is it advisable to burn in gamma correction or not? Or this does not matter so long as the image is correctly de-gammaed or gammaed as the case may be in the post-processing program.

 

4. Does the mr photographic exposure also affect gamma? How about the image control settings such as highlights/midtones etc?

 

5. When I bring in jpeg textures with the above settings for the diffuse, can I check 'Use system default gamma' in the import bitmap dialog box? Isn't this essentially the same as 'Use image's own gamma' (in this particular case viz. setting input bitmap parameter to 2.2)?

 

6. I've read that bump maps from, say xnormal or zbrush, & displacement maps & hdris have a gamma of 1. So here will the override to 1 option need to be checked in the import bitmap dialog? Does the same apply to jpeg bump maps created in Photoshop? Will saving the grayscale bump map in photoshop in any format other than jpeg cause it to have a gamma of 1?

 

Does the same apply to specular & any other grayscale images created in PS?

 

7. To confuse matters further, I've also read that certain HDRs can have a gamma of 2.2 burnt in. How can one find out what gamma a particular image has?

 

8. What is the most obvious way in which using an incorrect gamma workflow manifests itself in renders (so that one can correct oneself)?

 

Many thanks for your time & patience.

[Francisco Penaloza]

I'll try to answer some of your questions,

 

1._ to have maximum flexibility with your image it is recommended to use EXR at 32 Bits, this will give you the maximum bit dept in your image to control height bright areas and blacks, you will be able to illuminate interiors without light, up to some point, or make night shots out of day light render, well hard shadows will show wrong but you get the point you have a lot of light information so you can control as need it.

Most of the cases you don't need to do this extreme changes, so then 16 Bits will be enough.

 

2._Yes if you save to 2.2 you are burning the gamma in your image, you have to save your image to 1.0. Sadly Photoshop do not have many tool for 32 Bit. so it forced you to switch to 16, unless you use external plug in such Magic bullet.

My workaround is to load my 32 Bits gamma 1.0 image and adjust the exposure until it look fine, then I convert that layer in smart object, then I change the bit depth of the file to 16 bits, you can use all the tools now, if a change in need it in the exposure of the beauty pass I go inside of that smart object and voila, 32 bit flexibility again.

 

3._if you say you wan to work LWF then you should not burn the gamma, until the very end. if you burn gamma you loose some light flexibility, and no you wont burn in hell , if you think your image look good already in Max buffer, you can save as JPG at gamma 2.2 and finish in photoshop no problems. The idea of LWF is keep consistency during the whole production chain. This in a studio with several artist and different software is very important, if you are one men band it is more flexible

 

4._MRPhotographic exposure only control that, exposure, in theory you could not use it at all, just setup your light and click render, but everything will be so bright that you wont see anything, but all the light info is there. Setup your exposure to make your image look as you need, then just save it at EXR at gamma 1.0 and you can keep working in LWF.

 

5._This varies, because most of the images on the net are already gamma 2.2 so you should leave default, unless you see the image displaying strange color, too dark or too bright. default is 2.2 and should be fine most of the time.

 

6._no, most of the gray scale images are 2.2 you don't need more than that, I think the code only will use 256 color, some else may correct me on that. ZBrush uses normal displacement map also and that is different than gray scale images, then you may use a little extra bit depth info.

 

7._This is from a photographer website:

"Technical Note on Camera Gamma. Most digital cameras record light linearly, so their gamma is assumed to be 1.0, but near the extreme shadows and highlights this may not hold true. In that case, the file gamma may represent a combination of the encoding gamma and the camera's gamma. However, the camera's gamma is usually negligible by comparison. Camera manufacturers might also apply subtle tonal curves, which can also impact a file's gamma."

 

Also some photographers create HDRI from JPG (this are gamma 2.2) and others uses RAW(Posible 1.0) then the difference in gamma.

 

 

8._LWF is more than just gamma, it is about keep consistency during your work flow, and keep maximum bit depth in your image, so you can do changes all during your process. if you setup your 3D software to LWF and get your image looking just as you want it, and you save it to JPG but with gamma 1.0 your image will look dark, way darker than your Render buffer, and there is no way to bright that image.

If you save it as JPG at gamma 2.2 you can work the image no problems but if you have burn whites on it, you won't be able to fix them, no because the gamma but because the low bit depth of JPG files.

 

With a fixed gamma during your whole work flow and a wide bit depth you have more light information to control your image, some people does not need all this, so 8 bit is just fine, then just be sure to have the correct gamma in and out of your 3D software.

 

hope this help you, and hopefully some else jump in to clarify or rectify anything that I said

good luck.

Edited September 3, 2014 by fco3d

[SgWRX]

another interesting thing in working with photoshop from max rendered images is color space. i have my monitor profiled via a gretag mcbeth monitor calibration tool (now xrite). when i was working in max 2011-2012, i would save my render from the rendered frame window as a jpg usually, then open it in photoshop and when photoshop said there was no tagged profile, i'd assign either "sRGB" or "monitor_xyz". in max 2014/2015, i have to for sure assign "monitor_xyz" when opening because "sRGB" is dull - which makes sense as my monitor is showing me the rendered frame image. ha!

 

anyway the best thing to do is assign it the monitor profile (and by this i mean the one created with the color calibration tool, which is named and saved and used by windows). it can still retain the 16bit or 32bit colors. at least it's a base to start with.