Category Archives: Post Processing

Correcting White Balance in Digital Images using expodisc 2.0

Of all the autoexposure features available in modern DSLRs, the one that is most frustrating for me is the Auto-WB.  For years, I set the white balance to Auto-WB, hoping to be fine with the color in my digital images.  Again, for all those years, my mind wasn’t tuned to deciphering the color issues.  Recently, I noticed that some of my landscape shots looked too blue to me.  Talking to a former photography student and now a good photographer himself, Sanjiv Kapoor, I learned how to adjust the color temperature and the tint sliders in Lightroom to get the right colors.  Furthermore, I learned the idea of using a WB filter to reduce the guesswork involved in this exercise.  Here’s how.

This is my process for RAW shooting.  I attach an expodisc 2.0 WB filter to the front of the lens, in the light condition of the main shot, to make a reference image at metered exposure.  It produces a perfect (18%) neutral gray image.

Neutral Gray Image

Neutral Gray Image made with a WB filter in the same light as the image subject.  Caveat – if you are viewing this post in a monitor not correctly color calibrated, you are not seeing neutral gray.

Once opened in Lightroom, the default may not open up as neutral gray.  It will open up with a default color temperature and tint, that may not be the real color temperature/tint.  Drop the eyedropper from the Lightroom Develop Module into this image.  That neutralizes any color cast in this reference and gives you the right white balance.  Just apply the same color temperature and tint to the desired image.  It is quite easy to do this in Lightroom, by simply “sync”ing the develop settings.  In fact, I spend my time long enough on this reference (see the dust spot in it – I correct that, plus apply the lens profile etc), before “syncing” it to all the frames shot in the same light.

Here’s an example.  As opened in Lightroom, the top image shown here is how it looked.

Image as seen after Lightroom opened RAW file

How this image looked when RAW file was opened up as default in Lightroom. Too blue and not representing what was seen.

This is too blue and did not represent what was seen.  The color temperature was 5750 with a tint of -4.  The neutral gray reference shot shown earlier had a color temperature of 8800 with a tint of -5.  Upon correcting this image to that, the resulting final image is shown below.

Image with corrected white balance

Image with corrected white balance, with the aid of the expodisc 2.0

This represents what was seen.

Now that I have figured this out, and now that I have tuned my mind to seeing colors a bit better, I find all kinds of color errors all over my portfolio from years of work!!  :-)  As I find time, I will keep correcting the color of my past photographs, but I don’t have the reference shots to help me.

NOTE: The user’s manual for expodisc 2.0 talks about a different way to use it.  Take a reference shot into the camera, by using a setting for white balance reference shot.  Then the following images will be rendered correctly.  In my honest opinion, this method is appropriate for jpg shooters.  The method I outlined here is more suited for RAW shooters.

Red Streak Noise in Long Exposure Night Shots Solved

Last Saturday, I was photographing along the California Hwy 1 coastline at night.  It was pretty dark requiring long exposures.  With that came a noise problem – a red streak in the image.  See below.

Long Exposure Night Shot of Sea Stack showing red streak noise

Long Exposure Night Shot of Sea Stack along California Hwy 1 Coast. See the two red streaks in the lower one-thirds of the image.

This was an eight minute exposure.  Shot at f22, ISO100.  Nikkor 70-200mm f2.8 lens and Nikon D4S body.  Fortunately, I had another two minute exposure of the same composition, made when there was a bit more light that would work for me as a keeper.  So, I had not lost the shot.  But, it was disconcerting to realize that I was limited to two minute exposures with this lens for night shots.

First, I wanted to ascertain that the red streak noise was repeatable.  I ran a series of tests on long night exposures yesterday, only to realize that with this lens, it was very repeatable as long as the scene was pretty dark and my exposure was greater than 2 minutes @ ISO100.  I also verified other ISOs and found that the red streak noise found during 4 minutes @ ISO100 and that found during 1 minute @ ISO400 were about the same.  There was no escaping this.  If I needed to shoot in very dark conditions – I will not be able to get away with shorter exposures, using ISO to compensate.  This was depressing …

Next, I attempted to see if “long exposure noise reduction” would compensate for this issue.  After all, the long exposure noise reduction works by making a dark exposure with identical parameters, with the shutter closed.  The idea is that the noise on the sensor would be same, which is later subtracted from the main image, thus reducing or eliminating to a great extent the noise resulting from long exposure.  The results of these tests were disappointing as well.  The noise was the same in the RAW files, but slightly reduced in the in-camera JPGs.  I shoot 100% RAW and would not be happy switching to JPG for the slight reduction in the red streak noise.  I needed to solve it fully.

As I drove around and lived my life today, it occurred to me that I should perhaps try to apply the long exposure noise reduction idea manually.  At the next opportunity I got, I put the lens cap on the same lens and made an eight minute exposure at f22 and ISO100.  The resulting dark exposure with red streak noise is shown below.

Dark exposure with lens cap on, recreating the red streak noise alone.

Dark exposure with lens cap on, recreating the red streak noise alone.

Now, I had to figure out a way to subtract the red streak noise seen in this image, from the original image.  Since I have been stacking images in Photoshop for years, this was easy for me to figure out.  Here is the procedure:

1. Load both images from LR into PS as layers.

2. Right-click the layers in PS and “Convert to Smart Object”.

3. Pull-down “Layer” > “Smart Objects” > “Stack Mode” > Range.

Stacking using “Range” makes sense, because it is essentially subtracting the maximum signal from the minimum signal and providing the difference.  Since the second image (containing only the red streak noise) has black in the rest of the image, only the red streak noise will get eliminated.

I tried this procedure and “bingo”, it worked.  The red streak noise was eliminated and there was no loss to the image quality.  All details of the underlying image came alive just as I had imagined.  The resulting red streak noise free image is shown below.

Red streak noise has now been eliminated in this image, using the procedure mentioned in this post.

Red streak noise has now been eliminated in this image, using the procedure mentioned in this post.

Conclusion – While I have not solved how to prevent the red streak noise in the first place, I have a pretty good procedure to deal with it in post.  Just take another image with the same exposure parameters as the real image, with the lens cap “on” this time.  This may be done several days later and in conditions different from the shoot.  Then, subtract the latter from the former using the PS procedure just outlined.

PS.  I have observed this red streak noise in my Nikkor 70-200mm f2.8 VR lens.  Others have reported it on the Nikkor 16-35mm f4 lens.  I checked my 16-35mm f4 lens and do not see this noise in that one.

If you have seen this type of red streak noise during long night exposures, please try this procedure and let me know if it worked for you.  I would appreciate it, if you could post your success story as a comment here.  Thank you for your attention.

Changing A Portrait Background Using Photoshop CC

I made this image of a Demoiselle Crane and wasn’t happy with the way the background turned out.  Overall, I got the eyes to be sharp and the background to be blurred out, but I would have preferred not to have the gray at the very top.  I decided to rectify the background in Photoshop CC and here is how I did it.  By no means do I mean that this is the only way to alter a background in Photoshop.  This is just the way I chose to do it.

Demoiselle Crane (as shot)

Demoiselle Crane (as shot). I was not satisfied with the gray in the top background. The following is the process I used to make the background uniform.

I began by taking a slice of the preferred green from the left side of the image and creating an identical sized frame full of that green.  There are many ways one could have created this background image, but here is how I did it.  I cropped a small portion of the left of the bird and in Photoshop CC, scaled that image to the same size as the main bird image.

Background for the image.

Background for the image, created by cropping a small portion of the background from the “as shot” image. Then, rescaling to match the dimensions of the main image.

Now, I have two files in Lightroom (LR), the first one being the as-shot image of the bird and the second one being this background.  Choose both of them in the Library module of LR and right click to open them as layers in Photoshop.

Opening the main image and the background image as layers in Photoshop CC

Opening the main image and the background image from Lightroom as layers into Photoshop CC

The two layers can be seen in the layers panel of Photoshop CC.

Layers in Photoshop CC

Layers in Photoshop CC

Using the layer mask icon of Photoshop CC, open a layer mask for the top layer, which is the layer for the bird image.

Adding a layer mark

Adding a layer mask

The layer panel will look like this.  The white is the layer mask.

Layer Mask seen in the layer panel

Layer Mask seen in the layer panel

Then, Select > Color Range, to make a selection in the layer mask.


Using “Color Range” to make a selection

This results in the following automatic selection.

Initial selection using

Initial selection using “Color Range”

In this selection, white is see through, while black is blocking.  Imagine the layer mask to be on top of the layer.  Wherever there is white in the mask, the underneath layer is revealed and wherever there is black in the mask, it is hidden.

So, this mask reveals most of the bird, but notably, the eyes will be hidden and parts of the neck will be partially hidden.  This is not what we want.  Despite this, the initial color range selection is of great help, because the edges are detected well and we don’t have to laboriously select the edges and make all kinds of ugly errors in the process.

Notice the three eyedropper icons just below the “Save” button.  The dropper with the + sign when enabled and used, will add some colors of the image to the mask selection and the dropper with the – sign when enabled and used, will remove some colors from the mask.  I played some with these two droppers and ended up with this mask.

The mask, after tweaking with the eyedroppers.

The mask, after tweaking with the eyedroppers.

Still not perfect.  I want the whole bird to be clearly visible.  The gray areas of the mask will partially hide the bird.  To correct this, I pick a feathered brush and painted white in the gray areas inside the bird, making sure that I don’t go too close to the edges.  I end up with the following mask.

Mask, after painting with white inside the area of the bird

Mask, after painting with white inside the area of the bird

Sidebar Tip – when you want to paint on the mask, sometimes, it is not visible on the screen.  To make it visible in the main screen, press the “\” key, which is usually above the “Enter” key.  This makes it visible in red and white.  To make it visible in black and white, now use the “`” key, which is usually above the “Tab” key.

This corrected mask (above) is pretty good.  I now have a mask that will precisely reveal the bird.  Coming to think of it, what I really need is a way to reveal the background from the background layer, and so I decide to invert this mask.

Inverting the mask

Inverting the mask

I want the white area to be perfectly white.  So, I take a brush and paint the background area totally white in this mask, being very careful not to paint over the edges.

Final mark that looks good.

Final mask that looks good.

At this point, go back and look at the layers panel.  If we want to hide the bird and reveal the background, this mask needs to be in the layer that has the background.  But, now, this mask is in the bird layer.  This can easily be corrected.  Drag the mask from the bird layer to the background layer.

Moving the layer mask to the background layer

Moving the layer mask to the background layer

Now, the layer mask is in the correct layer.  Still the image looks the same as the original.  No change.  That is because the bird layer is on top of the background layer.  Let us reverse this.  Push the whole background layer, including the mask, to the top.

Reversing the order of the layers in the stack

Reversing the order of the layers in the stack

To be clear, in the top layer, the background layer and the mask both exists.  The mask has black all over the area containing the bird, meaning – the bird is blocked in the top layer, while fully revealing the background.  Therefore, we are able to see the background from the top layer.  The black area, since it blocks the top layer from being visible, reveals the underneath layer, the bird itself.


Final Image of Demoiselle Crane

Final Image of Demoiselle Crane

One request – if you like this post and feel that you have benefited from it, please pass a link of this post to a friend who may appreciate it.  Furthermore, please visit my Facebook page – and “like” it.  Thank you.  As always, comments are always welcome.