Post Processing ND filter - DPChallenge Forums

Nikon AF-S DX NIKKOR 18-200mm f/3.5-5.6G ED VR II

09/30/2005 08:14:17 AM · #1

Does anyone know of a post processing technique that will produce the same effect as an ND filter? I assume dodge and burn could get the job done but I think that would count as spot editing.

kosmikkreeper

Nikon D300s

09/30/2005 08:21:32 AM · #2

You might wanna look at this site. They have a whole bunch of filter pluggins and they work really great!

conglett

Nikon D70

Nikon AF-S DX Zoom-Nikkor 18-70mm f/3.5-4.5G IF-ED

09/30/2005 08:35:58 AM · #3

Nope. ND filters shift illuminance relative to the scale of the camera sensor. Once the shot is taken you can only modify pixes values that were in its range. For example, a ND filter can bring back into range what would have otherwise been a blown out part of the image, at the expense of potentially pushing the darks beyond the lower range.

The closest thing you've got in post-processing is Curves in Photoshop, but its not the same.

dr rick

Canon EOS-300D Rebel

Canon EF 28-135mm f/3.5-5.6 IS USM

09/30/2005 10:33:56 AM · #4

An ND (Neutral Density) filter just reduces the amount of light entering the camera, allowing use of a longer shutter speed (to create motion blur) or wider aperture (to throw the background out of focus). These effects can be simulated in post processing using various blur tools (although it would need to be selective, thus spot editing).

If you just want a darker photo, you don't necessarily need an ND filter. Just underexpose it or adjust the brightness during postprocessing. But if you've overexposed the image and blown the highlights, there is no way to retrieve the detail in postprocessing.

Bear_Music

Samsung Galaxy S24 Ultra

Sony 24-70mm F4 Vario-Tessar T* FE OSS

09/30/2005 11:08:22 AM · #5

Think of a plain neutral density filter as being a means of either increasing shutter speed at a given f/stop or increasing aperture at a given shutter speed, without compromising the exposure. 'Cuz that's all it is.

Now, if you're asking whether you can simulate a GRADUATED ND filter in PS, the answer is yes up to a point. As rick pointed out, nothing you do can save blown-out highlights. But if the image is properly exposed for the bright areas, you can select the dark areas and bring them up (compress the tonal range of the image) and this is essentially the function of the graduated ND filter; to bring the brights closer in value to the darks, particularly the sky.

Robt.

Sony 24-70mm F4 Vario-Tessar T* FE OSS

09/30/2005 11:16:29 AM · #6

Thanks for the clarification bear_music. I am actually talking about a graduated ND filter. I should have been more specifc. I am trying to use it to expose the ground properly without overexposing the sky.

Bear_Music

Samsung Galaxy S24 Ultra

09/30/2005 11:27:38 AM · #7

Originally posted by qbicle:

OK, now we're cooking. Bear in mind that a ND filter is just a straight line dividing an image. So it's a pretty crude approximation most of the time, except for like seascapes where you have a truly level horizon.

So the goal is to balance a brighter sky with a darker foreground: as long as your sky and foreground values aren't MILES apart you can accomplish this pretty easily with photoshop. When there's a really extreme tonal range to deal with, it's a bit tougher. It's possible to combine components from 2 separate exposures into one, but that's pretty advanced and presumes a static subject and a tripod.

Anyhow, what I need to know is, do you use Photoshop? And if so, which version?

Robt.

Sony 24-70mm F4 Vario-Tessar T* FE OSS

09/30/2005 11:44:15 AM · #8

Right now I am using GIMP2.0.

Bear_Music

Samsung Galaxy S24 Ultra

09/30/2005 11:49:51 AM · #9

Originally posted by qbicle:

Right now I am using GIMP2.0.

OK... I haven't used the GIMP so can't be sure how you accomplish things there, but I know it can emulate virtually everything Photoshop does.

In the latest versions of Photoshop there's a whole dialogue box called "shadow/highlight adjustment". In earlier versions we do shadow and highlight masking, the new versions automate that.

To make a highlight mask, we hit contrl-alt-tilde (~ = tilde) and a blended selection of the brighter parts of the image is made. We then hit cntrol-j to create a layer mask from the selection. Then we go back to the base layer, hit cntrl-alt-tilde again, then INVERT the selection and use cntrl-j to make a layer mask of the inverted (shadow) selection.

We then set the blending modes of those two layers to multiply (for the highlights) and screen (for the shadows) and adjust the relative opacity of those two layers until; the balance is as you wish it.

Whether the Gimp has the equivalent I do not know.

R.

Message edited by author 2005-09-30 11:51:17.

09/30/2005 03:27:17 PM · #10

Thanks for the reply bear. I will check it out this weekend and see what I can find.