Category Archives: Lightroom

What you Need to Know About Histograms

Original Publish Date: 11-September-2013
Last Revision: 11-April-2016

If you ask us what is the most potent tool a night photographer can wield, we’ll tell you: the histogram.  Unfortunately nearly all of the histogram information available seems to spend too much effort talking about what a histogram should look like and not enough time explaining what a histogram is… or that there are many different histograms and not all are equally useful. For example there are: luminosity histograms constructed from thumbnails created by the camera, there are color histograms created from the same thumbnails, and then there are luminosity and color histograms based on the actual sensor data – but those are rare. And of course there are still more histograms.

In the Beginning [41_03766]

In my early days I took what I thought was a fabulous photo of the fog creeping up against Mount Allison. It looked SO good on my LCD that I knew I was going to be in love with it. When I got home I realized that it was far from ideal. It was woefully underexposed and very noisy. That’s because I didn’t think to look at the histogram. At the time noise handling was not great and it wasn’t until recently that I was able to tease a half-decent image out of the data.

Deconstructing A Histogram

The best way to understand a histogram is to experiment. But before we launch into some experimentation, let me take a stab at explaining what a histogram is.

A histogram is a graph that shows the distribution of brightness (luminosity) over the range from the darkest possible to the brightest possible pixel.

Each vertical column reveals the number of pixels in the image that have that brightness level.  Usually the left edge is the darkest possible pixel – black – and the right edge is the brightest possible pixel – but there are some variations in histograms which we’ll cover in a moment.  Here is a degenerate, but perfectly valid histogram.


A histogram showing only three brightness levels – nothing brighter than mid range.

In the graph above, we see that there are some (we don’t know how many) of the darkest possible luminosity.  A lot of pixels that are relatively dark – corresponding to the tallest line, and a few pixels in the “midrange” of possible brightness values at the next stubby little line. The image from which the histogram was made is this one:


A degenerate image composed of several primary colors.

Looking at the image, it is pretty obvious that the little bump on the far left of the histogram is the black frame around the border. The tall line in the histogram is the brown, and the little bump near the middle is the orange color.  What may be puzzling is that the orange looks pretty bright and you would not expect it to fall only about half way across the range from darkest to lightest values. In fact there IS clipping in the red channel – but we don’t see that in our luminosity histogram above! We’ll see why in a moment.

post-it-note-thIf one of the columns reaches the top of the graph it does NOT mean a “blow out” has happened. Likewise if a column appears at the right or left edge of the graph it does not mean that data has been lost or “blown out” – it does indicate that there MIGHT be a problem.


At right is another histogram for the same data, 4 of them, actually. This was created using Photoshop’s “All Channels” view.

Rather than luminosity, the top histogram is in mode RGB showing each of the colors in this simple image against the maximum for that color.

The Red Histogram shows a complete range of reds from the darkest possible in the black border to the lightest possible. And here is where we first get a clue that quite a bit of the red is in the extreme right hand side of the histogram.  Most of the red is contained in the brown color.

The Green histogram shows the darkest possible green (i.e. black) and some green in the left 1/5th of the possible values, while the blue histogram shows only black and very dark blues.

Admittedly the image is not illustrative of a typical photograph of any kind. It does show clearly how the histogram corresponds to the values in the image.


The image was created from additive layers using blend mode Linear Dodge ADD. Each layer has been constructed in different colors using the color value shown.  It is easy to calculate the majority of RGB triplets as: R=128, G=64, and B=32+16 (48).  The maximum values for an 8-bit image would be 255,255,255 – the value of the “whitest possible white” in this color space.

You might expect that the graph would reflect the 16-bitness of a 16 bit image. The maximum values for each color then would be 65,536, not 255 – but that’s not the way Adobe shows it.  A 65 thousand pixel-wide histogram would be beyond unwieldy.

Did you just have an “aha” moment?

One reason why the histogram is not completely trustworthy is that it is a composite of many luminosity values being lumped into one.  How so? Imagine possible values from 0 to 65,000 shown on a graph with only 255 different columns. A lot of “lumping things together” is present! It is possible to have lots of data in the darkest column and in the lightest column and still not have any blow outs or blacks.  Imagine it this way, suppose there were 100 possible luminosity values, but the graph showed just 20 columns.  The leftmost column would include values ranging from 0 to 4, the rightmost (brightest) would hold values from 95 to 99. So, in theory, you could have no zeroes and no maximums, but your graph would still show you data at each extreme.  This is where the histogram in Adobe Camera Raw is much more useful and accurate. Or to be more accurate, it’s not the ACR histogram that shows that much additional data, but it does indicate when items are being “clipped” – that is, reach the maximum or minimum.  But we’ll get to that in a minute.

In case you haven’t had another AHA moment, we want to explain why the histogram you see on your camera LCD should be regarded with suspicion.  That on-camera histogram is created from the thumbnail JPEG which is also shown on your LCD.  To go from raw data to a JPEG involves lots of operations including scaling 14 bits of information down to 8 bits, taking megapixels of resolution down to kilo-pixels and applying default curves and color assumptions. With that much data manipulation going on, your histogram reflects what your image MIGHT look like as a tiny JPEG and therefore may not accurately reflect what you’ve captured.

Get A Better Histogram: Use Lightroom or Adobe Camera Raw

Below is a much more useful histogram as found in Lightroom or Adobe Camera Raw. Your camera is not going to give you this level of detail- though you might have a highlight and/or shadows clipping indicator which we recommend you use.  ACR and Lightroom both offer shadow and highlight clipping indicators. Clipping indicators are enabled using the triangles in the upper left and right of the histogram or with the “J” key which toggles both indicators either on or off.  If you turn ON the clipping indicates by default blue dots replace clipped shadows and red dots reflect clipped (aka blown out) highlights.

First the wide view.


Wide View: Shadow clipping (left arrow in histogram) turned on. BLUE indicates where the values have fallen to zero.

And here zoomed in:


Zoomed in: We see both clipping in the shadows and highlight clipping (circled -though there are many more).

Notice how in the 1/4 view, we see much more shadow clipping! If we zoom in to 100% it will be even more obvious. As we adjust the exposure, shadows, contrast, highlights, blacks and whites the histogram and the clipping indications are reflected in real time.

Lightroom is also giving you a hint which colors are being clipped.  The blue triangle at the upper right tells you that the blue channel is causing the highlight clipping.  When multiple colors are being clipped, the triangle will include all the colors added together. Here the white triangle for the shadow clipping tells us ALL colors are zero – that is clipped in the shadows.  For this image moving the exposure to the right reveals that the green channel is the most clipped. 

Take Aways

  1. Don’t believe everything you see on the back of your camera display – especially not the image!
  2. Don’t only pay attention to the luminosity graph – it may hide highlight clipping in one or more colors. This is especially true, for example, if you take photos of red roses. You can cause the red channel to clip but the luminosity graph will look fine.
  3. Take a look at the color histogram if your camera has one.
  4. Just because you are taking photos at night doesn’t mean you can’t blow out the stars. Doing so means you’ll lose some color data, but it’s better to blow out a few stars than to have black for your foreground.
  5. Not every histogram (in fact most) won’t be “bell curves” – especially not at night.
  6. Oh, and please shoot in RAW. You keep a lot more of what you shoot that way!

Clouds, Milky Way and Eerie Formations in Alabama Hills, CA


Tips for Using Layers for Stacking

Down Range

With hundreds of users of our Advanced Stacker PLUS, we get questions about workflow. What is the best way to manage files in Lightroom? What order should I perform operations, etc. While we have briefly given some hints in the comments for the Advanced Stacker, it seemed time to elaborate.

Of course it all begins with how you choose to organize your files. Organizational tips will come in a separate article as it would make this article too long.  Unfortunately Lightroom is not a particularly helpful tool to use for creatively stacking shots and that’s one of the reasons I don’t much like it. For my money Adobe Bridge is more powerful and flexible.

One particularly insightful exchange was with Dan B who wrote:

One minor gripe I have mostly has to do with incorporating the action into my existing workflow. For star trails my current workflow starts in Lightroom where I do any preliminary adjustments/corrections and then open the sequence as a layered document in Photoshop. I created a layer style which is my one-click way of changing the blending mode to lighten on all of the layers. Unless there is a way of applying the action to an already open layered document I would presumably have to adjust my work flow by moving the star trail sequence to its own folder, doing preliminary adjustments in ACR and then using the action as directed.

Beginning in Photoshop CS6, you can do a one button change of all blend modes and opacities of all selected layers. You can select all layers with Alt-Ctl-A  (Option-Command-A on a Mac).

PSMultiLayerOperation PSMultiLayerOpacity

The change applies to all selected layers.  Setting all the opacities the same won’t provide the nifty comet-style stacking.  There are some scripts out there to address variable opacity and other stacking tricks but there are restrictions. Installing a script isn’t always easy – depends what version of Photoshop you have, and no script I’ve seen is able to work from files. Scripts work on Layers. Scripts by design aren’t really meant to tackle repetitive tasks against a large number of files – that’s why actions were created.

Summary: There are two options: work on layers (actions or scripts) or work on files (actions).

There is no equivalent in Lightroom to do Photoshop Batch operations like you can from Adobe Bridge, and that’s unfortunate.

Another observation is that loading files into a stack in Photoshop and then editing individual layers is, SLUGGISH unless you have few layers – see later for just how sluggish.  Why would you edit layers? You might edit individual layers to remove things like airplane trails or bright light sources. Airplane trails are a lot easier to remove from individual documents than to remove after the stack has been created. However my recommendation is: don’t do editing in layers. Export the documents to TIFF or JPG and edit them individually. Why? Because then you can use the edited files standalone or stack them in different ways and NOT have a huge layered document. You also have more flexibility to use programs like StarStax which do not work well with RAW files (StarStax does not know how to apply all of your ACR or Lightroom edits). Alternatively, you can load files into a layered document, edit the layers and then use a script (Export Layers to files) to save layers as individual files.

Load Into Layers from Lightroom


Save From Layers into Individual Files


If you save from layers into files, Lightroom will not know where those saved files are unless you Import or Resynchronize the folder where the files are saved. Bridge, on the other hand, doesn’t require importing or synchronizing – though you may need to do a refresh operation. By the way the Photoshop “Export Layers” operation insists on adding a number prefix to each of your files… and it will make a mess if the opacity of each layer is not 100%.


If you want to do your stacking using layers, there is one more thing that might change your mind… speed.  We ran speed tests on two different machines comparing the end-to-end time needed to create stacked documents using the layering method with the automated Advanced Stacker Plus.  We were shocked by the difference.  For each machine we stacked 60 RAW files from a Canon 5D Mark II. In each case we applied a linear adjustment to all files, and made a tweak to the color balance.  We drove the layering method using Lightroom 5’s “Edit as Layers” operation. For the Advanced Stacker PLUS we drove the operation using Adobe Bridge CC. We kept Bridge CC, Lightroom 5, and Photoshop CC loaded in each machine so that the same starting memory footprint was used. And to make sure there was no advantage from using pre-loaded files, we used a different set of 60 files for each comparison.  The file sizes were identical.

The less speedy machine was a quad core AMD Phenom II processor with 6Gb of memory, Windows 7 Home Premium, 64 bit. The new machine was an Intel I7 quad core machine with Windows 8, 64bit, and 12 Gb of memory.

On the lower end machine it took 33 minutes to load 60 Raw files as layers, change all the layers to blend mode Lighten* and merge those layers. There was HEAVY swapping and the machine was extremely sluggish.  Using the Advanced Stacker PLUS to perform the same result took 8 minutes and the machine never became unresponsive – because there are never more than a dozen layers in memory.  The Advanced Stacker PLUS took 76% less time!

*NOTE: In Photoshop CC and Photoshop CS6 all the blend modes are changed with one Select All Layers command and one blend mode change.  On the sluggish machine it took almost 2 minutes for the “Select All Layers” key sequence to complete!

On the faster machine the results were similar: it took 19 minutes to load all the layers, change the blend mode and merge the visible layers into a single image for saving while it took 3 minutes to use the Advanced Stacker Plus.  On the 12 GB machine there was some pretty heavy disk operation going on when using layering, but memory did not top out. The Advanced Stacker PLUS took 80% less time.

In each case, adding more layers will make the stacker speed advantage even greater because once the machine maxes out memory it becomes a performance dog.  We’d love it if you’d run a comparison on your hardware to see what your results are like.

In Summary

There are many folks out there who are proponents of stacking star trail shots using layers. I’m not a fan.  Certainly using layer provides some benefits, but it also comes with some (high) costs.  Here are some tradeoffs to help you decide whether layering shots in Photoshop will be more effective for you or not:

Layer When

  • You have LOTS of memory and patience.
  • You have fewer than about 30 layers (shots) or your individual shots are small.
  • You don’t expect to save the final image as a layered document (only .psb files allow sizes big enough to hold a typical layered document)
  • You don’t mind throwing away any editing you do in a single layer (e.g. removing plane trails, stray light, etc.)
  • You don’t mind manually updating blend modes and opacity or finding installing and using the (very few) tools available to help with layer adjustments.
  • You intend to do something totally different from all the currently popular effects (Comets, streaks, etc.)
  • You don’t plan to make a timelapse – or if you do, you can live with the restrictions created by a layered document.

Stack via an Action or External Tool When

  • You have a boatload of images or limited memory.
  • Want to create intermediate images for timelapse/animation.
  • You intend to pre-edit individual frames to clean them up before creating a final version.

The Cloud is a Clod

Earlier I talked about some things you should know about Adobe’s Creative Cloud method of licensing software. As of today, Monday, May 6. 2013  it became the ONLY way.

It’s a shame because just as their Cloud service has it’s strengths and WEAKNESSES, their sales implementation shows only weaknesses. For example, depending on how you find them, you get significantly different pricing. I went here, to get the pricing below. If you go to the regular front page, you’ll not see something as inexpensive.

Here is an example that apparently is “too good to be true” – a full Cloud license for $20 for the first year.


Unfortunately when I travel down the path to try to buy it (clicking the Join button):

But wait… here is what I own, according to ADOBE!

I suppose I should NOT be surprised that Adobe has managed to further trip over themselves and confuse the heck out of people like me with conflicting pricing.  I would love to see Adobe take a Netflix Style hit for this failure.  In the long run, their strategy may work, in the short run, I see it as another failure.

What Photoshop?

Not long ago I took Adobe to task for a poorly executed upgrade path from their expensive Photoshop CS5 to Photoshop CS6. Today, I am calling them on the carpet for their most egregious mistake:

Confusing the H*LL out of their potential clients with an armada of similarly named, poorly differentiated, expensive products. To the casual observer the cost of that fleet of products ranges from expensive to “I have to forego buying a camera so I can edit my photos” expensive.  Nearly daily my students ask me whether they should buy Photoshop and WHICH ONE!

The discontinuation of sale of Photoshop through normal sales channels has simplified the picture considerably since this article was originally written. The choices are:
Photoshop CC (through Creative Cloud), Photoshop Elements, and Photoshop Lightroom (Creative Cloud OR retail sales).  However it’s worth reading through the rest of this article for some historical perspective. 

Isn’t Photoshop Too Expensive?

Let me weigh in on the expensive part first.  Photoshop CS6 Standard Edition (I’ll try to disentangle what that means in a moment) ranges from about $600 at Amazon to $700 directly from Adobe it sure sounds expensive.  But if you think of it as you would  say a sweet new lens for your camera it suddenly sounds less outrageously expensive. If you are willing to invest in Adobe’s future by taking a chance on their wobbly Cloud offering you can “rent” Photoshop for as low as $50 per month (or $20 per month depending on the plan – or even as little as $10/month).

So yes, it’s expensive. The question is: will it make your photos more impressive like a $600 lens might? My answer is yes, if you’re willing to do the time learning Photoshop’s incredible awesome power and escape Photoshop’s maddening quirks.

And for the kind of photography that I do: night photography with layers and complex operations there really is no equal that I am aware of.  GIMP is a free independently written Photoshop alternative. At the moment it is limited to 8 bit operations – though a 16 bit version is in beta. For many years I couldn’t bear the outrageous price of Photoshop so I used PaintShopPro with great success. Eventually I realized that the power I wanted required a payment so I stuck my toe into Photoshop CS3. Later it was CS5 and most recently CS6.  Of course since it is my business to produce prints and teach students about night photography, I get to deduct Photoshop as a cost of doing business. That doesn’t make it cheaper, though, does it.

What Version of Photoshop?

As I noted in the opening paragraph, Adobe has really made a mess of their products.  Here is a PARTIAL list of Photoshop choices for the LATEST version and the cost of each as reported on Adobe’s website. Costs are rounded to the nearest tens.

  • Photoshop CS6 $600
  • Photoshop CS6 Upgrade $200
  • Photoshop CS6 Extended $1000
  • Photoshop CS6 Extended Upgrade $400
  • Photoshop Elements 12 $100
  • Photoshop Elements 12 Editor ?
  • Photoshop Elements 12 with Adobe Premiere Elements $150
  • Adobe Photoshop Lightroom 5 $150
  • Design Standard CS6  $1300
  • Design and Web Premium CS6 $1900
  • Production Premium CS6 $1900
  • Master Collection CS6 $2600
  • Creative Cloud $240/year OR $350/year OR $600/year

The underlined items are bundles that contain Photoshop in them, that’s why they are more expensive.  The items in italics are in fact not really Photoshop except in name.  Think of them as Photoshop Light with simpler interfaces and fewer features. And the above does not show the Student/Teacher pricing which is yet another kettle of smelly fish.

In a nutshell for the kind of photo processing I do, Photoshop CS6 (not Extended, and definitely not Elements) is the tool of choice.

If you’re wondering whether you need the latest version: probably not. CS3, CS4 or CS5 will do just fine if you find them discounted somewhere and are careful to buy the FULL package, not an upgrade. Beware as there are many counterfeiters and scams – only buy from a reputable company.

What Adobe Tool Do you Need?

One more frustration for me is that Adobe does a very poor job differentiating its products.  You have to be a student of Adobe to understand how Illustrator differs from Photoshop from In Design, from Lightroom, etc. Or worse if I want to make a timelapse video which tool is the best one: Premiere Pro, Premiere Elements, After Effects, Photoshop, Photoshop Extended, Encore?  It’s hard to say unless you have an PhD in the Adobe marketspace – I don’t.

But You Haven’t Mentioned Lightroom!

You noticed that, eh? I own it, but I don’t like Lightroom. The photo editing interface for Lightroom is much more intuitive than the one in Photoshop, and Lightroom lets you sort, tag, organize and catalog photos with some really great features. My pet peeve is that Lightroom is slower than a frozen slug in a snowstorm and it forces me to “Import” everything I want to work on. Lightroom doesn’t do layering which is the key thing I need for optimum photo results.  The free Picasa tool (from Google) does the cataloging, sorting and keywording I want along with less impressive, but passable photo editing.  The Picasa method for straightening photos is awesome, quick and dead simple. Besides, most everything Lightroom can do Photoshop or Photoshop plus Bridge (or Adobe Camera Raw) can do more powerfully – if you can figure it out, that is.

Still, Lightroom does provide some pretty powerful features and allows non-destructive editing. But at a cost both in $ and time.

Bottom Line?

Photoshop is powerful. You can go farther with it than without it, and best of all there are a LOT of resources around to help you learn Photoshop – like and books by Harold Davis (and many others).  Unfortunately lots of resources are needed because while Photoshop is a powerful weapon it is also a many-headed monster that requires developing some good wrestling skills.