Exposure/Fstop adjustments in shake

#1

Hey guys, I’m currently doing some research for my major project and I’ve hit a bit of a brick wall over one of my shots. Essentially I want to do an exposure adjustment on a scene rendering in a high dynamic range format, unfortunately I haven’t yet worked out how to recreate a change in exposure/fstop in shake. I naievely thought it would just be a brightness adjust on a HDR image but this doesn’t give me the effect I’m looking for. Does anyone know of a way of doing this exposure switch effect in shake?

Thanks
Matt B

#2

i know what your talking about, the look that is.

Im doing the same with a scope plugin im just writting to learna bout shake

What i do, is adjust brihness of corse, but you get a grayishness, so id screw wtih color adjustments and add some gray

or lessen the contrast. Basic photography, isnt less Fstop less contrast AND brightness? its been awhile lol

#3

what format are you working in ?

.hdr, .exr, hdr .tif,

make sure that your comp is in float space. otherwise it wil clip and give you grey.

also make surre that your colour operations are concatenating !

#4

When you ask about a change in exposure/fstop, are you referring purely to the exposure or are you looking to change the depth of field and edge sharpness as well?

#5

The easiest way to do this stuff with predictable results IMO is to work in linear floating point and here is my understanding of what to do:

I’m assuming that your HDR images inherently have a gamma of 1.0, this means that you must cancel out the monitor gamma adjustment and the image will look correct.
So import your OpenEXR (say) image and add a viewer lookup gamma LUT that is equal to your monitor gamma.
An fstop is equal to double the exposure, therefore add the image to itself (using an add node) to increase the exposure by 1 fstop, or use the brightness node, which is a multiplier, so brightness=2 means multiplied by two which is 1 fstop more light, or brightness=4 is 2 fstops more light. Also brightness=.5 is equivalent to 1 f-stop less light etc.

If working with say 8 bit linear images, first promote to float, then cancel out the gamma value, which is probably 2.2, using a gamma node. If you apply a brightness then, you will notice it holds together much better than not doing the float/gamma adjustment.

I actually found the elin docs useful (you can download from redgiant.com) for working out what’s what. Also prolost.com etc.

Michael

#6

You can change it with a Loglin node.

In Loglin make the r/g/bOffset to 90 or -90 per stop you want to increase/decrease(±45 is of course a half stop).

If your working in linear color, add a loglin, change it log and adjust the r/g/b/Offset, then add another loglin and go back to linear color.

(I already posted this to your question on highend, but I thought I would post it here too)

#7

thanks for your help guys (and thanks for replying in my other thread too beakre) I had an inkling that it would involve something in log space but I wasn’t too sure. I’ve found the modifying the rBlack and rWhite controls give the most controllable results, changing the r g and b offsets can give some odd looking results.

#8

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