Tag Archives: histogram

Link Roundup 09-30-2010

Don’t forget that we have ongoing themes in our Flickr pool and I’ll be selecting my favorites on the topic of “Camera Porn” sometime next week. We only have a few entries in the pool, so be sure to see here for details on participating.

Link Roundup 05-15-2010

Photo Editing With Histograms: 6 Basic Settings

The image histogram is often viewed as a thing of “extra information” and treated as a “good way to check for clipping”. While it’s true that the histogram provides a good check for highlight and shadow clipping, it also serves a greater purpose in post processing. Our mortal eyes are no match for the mighty histogram when it comes to tricky photos. Understanding the histogram and how your image editing software interacts with it can greatly improve your productivity and quality output.

In a recent article, I went over “How to Read Image Histograms” while providing some visual examples in the realm of brightness and contrast — two very basic concepts when it comes to photography. Now, we explore how the histogram and image are affected by other basic post-processing adjustments. For the purpose of this article, we’ll be looking at the tools available in the “Basic” panel of Adobe Lightroom and Adobe Camera Raw (other packages should have similar tools available).

These tools have unique and specific effects on the image and the image histogram. With the basic tools presented here, you should be able to manipulate your image within 90% of its final stage — further adjustments will come from more advanced tools (which we’ll look at in the next article).

In all of the examples below, I’ve added +50 to the base contrast setting so the effects of the adjustments can be visualized more clearly.

1. EXPOSURE

This adjustment acts much in the same way camera exposure does, by basically shifting the entire histogram to the left or right. This has the effect of brightening or darkening your overall image. The shadows tend to be more anchored than the highlights, and you’ll notice some distortion of the histogram as you move the adjustment to either extreme.

Notice that as you increase the exposure, the contrast tends to increase slightly due to the anchoring of the shadows. And as you lower the exposure, the contrast tends to decrease. This can be seen by the change in the width of the histogram.

For “normal” exposures, you’ll just want to make sure the histogram is somewhere between the edges. If you’re going for a low-key or high-key image, you’ll want to push the exposure accordingly. If you have a well exposed capture, you shouldn’t need to adjust this setting very much.

2. RECOVERY

This adjustment is intended to recover highlights by pulling them back down a bit. Here, the shadows are completely anchored and the increased recovery lowers the tone value of the highlights and upper midtones.

In this example series, I’ve started with an intentionally overexposed image to show the effect. In practice, I rarely need to adjust above a value of 25 or 50. Go much further than that, and you end up pulling your highlights into a gray area, making the image look flat due to lower contrast.

3. FILL LIGHT

This adjustment is the exact opposite of the recovery tool. Here, we pin down the highlights and increase the tonal value of the blacks and lower midtones.

In this example series, I’ve started with an intentionally underexposed image to show the effect. In practice, I rarely need to adjust above 25 or 50. Go much further than that, and you start pushing your blacks into a gray area and losing contrast and tonal depth.

4. BLACKS

This adjustment is sort of an anti-fill light… it brings your shadows down further into the dark region while having less effect on the highlights. This is good to use when you have less than perfect blacks and you need to tug that histogram just a little to the left.

In this example series, I’ve started with an image of slightly higher brightness to better show the effects of this adjustment.

5. BRIGHTNESS

We went over the brightness adjustment in the last article, but I’ll add a few notes here. You’ll notice that it acts very much like the exposure adjustment, pushing the image brighter or darker (and moving the histogram to the right or left). But it does this in a slightly different manner. The exposure control is more directed toward the extremes of the histogram, while the brightness control is more directed toward the center of the histogram (midtones). It still moves your highlights and shadows, but it moves more of your midtones than exposure does.

In this example series, I’ve started with the default image of +50 on the contrast and no further adjustments.

6. CONTRAST

We also went over contrast in the previous article, noting that the wider histogram equates to more contrast. This is a handy adjustment tool to use when your histogram doesn’t quite reach the edges at the blacks and whites, or if your image looks flat due to a heavy midtone concentration.

And again, you can see that the brightness and contrast adjustments are tied together and not completely independent.

HOW IS THIS USEFUL?

Understanding your histogram allows you to process the photo on a technical front rather than on pure aesthetics. Understanding how these basic adjustments affect the image and the histogram will allow you to manipulate it with more confidence.

But don’t get too caught up in watching your histogram — in the end, the only thing that matters is a photo that appeals to your eyes.

How to Read Image Histograms

Reading histograms is an important skill to acquire in the world of digital photography. Most images from digital cameras will require some amount of post processing, particularly if you shoot raw format. And most of the processing can be done by viewing the aesthetics of the image as you go, but having the ability to read and manipulate a histogram will increase your productivity and output quality.

So what exactly is a histogram? And how the heck do you “read” one? Take this, for example:

At a glance, it doesn’t tell you much. But there are certain things that you can take from the histogram. No, it doesn’t tell you that it belongs to a photo of a deserted trailer half buried in the middle of the desert. It doesn’t tell you if the image is in focus or if your composition is good. It only tells you the tonal values of the pixels contained in the image — blacks on the left, whites on the right.

For this article, I’ll be looking at a black and white image and histogram in order to simplify things. Color histograms work on the same concepts, but with 3 channels rather than one.

MID CONTRAST AND BRIGHTNESS

This is pretty much a straight b/w conversion with no contrast or brightness adjustments. It doesn’t look too bad, but it isn’t terribly dynamic either. And if you look at the histogram, you’ll see that the pixels fall into a centered group with a little breathing room on the shadows and highlights. We’ll use this one as our baseline to compare against. The other histograms will show this in a transparent green.

LOW CONTRAST

You can visually recognize the lower contrast in this image, and that correlates to a change in the histogram distribution. The pixels near the black and white points have moved in toward a neutral gray, which gives the appearance of lower contrast. The whole thing has basically been squeezed to the center.

HIGH CONTRAST

Again, you can visually recognize the higher contrast in this image, and the histogram changed too. The pixels near center have basically migrated outward toward the blacks and whites, thus giving us more contrast. This time we’re squashing pixels from the middle outward.

LOW BRIGHTNESS

Lower brightness is just a shift of tones toward the black region. You can see that the entire histogram has been pushed to the left. Also notice that the tonal range has been decreased, as shown by a narrower histogram.

HIGH BRIGHTNESS

Higher brightness is a shift in tones toward the white region. Here you can see that the entire histogram has been pushed to the right. Also notice that the tonal range has been increased, as shown by a wider histogram.

THE FINAL IMAGE

You can see that I went with a high contrast, high brightness image for my final path. The histogram shows this with the wide tonal range and a heavy concentration of pixels in the highlights.

CAN YOU SEE IT NOW?

This chart shows a combination of contrast and brightness adjustments on the example photo. As you move from left to right (low brightness to high brightness), you can see the histograms shift to the right. As you move from bottom to top (low contrast to high contrast), you can see the histograms widen.

Click the image for a larger version

The reason I’ve posted this article is because I want to get into the topic of manipulating the histogram during post processing — using it to guide you in what adjustments to apply. So the next article will look at how some of the basic adjustments affect the histogram and the image. We’ve already covered contrast and brightness adjustments here, but there are a few others we’ll need to utilize.

In the meantime, here’s some additional reading on the topic of histograms:

Working With Image Histograms
Photoshop Tip: Understanding Histograms
Camera Histograms: Tones and Contrast
A Practical Guide to Interpreting RGB Histograms

Link Roundup 09-13-2008

A lot of interesting stuff happening this week in the world of photography.

Link Roundup 02-09-2008

Before we get to the links, I just want to mention quickly that we had our photowalk in La Jolla today. The turnout was awesome! I lost count, but I think probably 15 to 20 people showed up from across Southern California and one from North Idaho. Just about everybody in the shot below was part of our group, plus we had a few others that weren’t in the frame. We had a great time, and I’ll try to post a recap on Monday the 18th — that way people have a chance to get through processing some photos and put them up on Flickr and whatnot.

La Jolla Photowalkers

FOR THOSE AT THE PHOTOWALK: TAG YOUR PHOTOS “photowalking020908″. This will help everybody find the photos, and I’ll also be searching through Flickr and Zooomr for those tags to find photos for Monday’s recap. Now on with the links…

PROJECTS

  • The View From Below
    Neil Creek
    As a photographer, it’s important to think about the uncommon perspective, and get out of the habit of shooting from the same height all the time. This photography project asks you to take and submit a photo from less than 30cm (12in) above the ground. DEADLINE: 02-21-2008
  • Send me a postcard
    All Day I Dream About Photography
    Send Antoine a digital postcard of a place that describes the area you call home. It should be interesting to see all the different places we come from! DEADLINE: 02-29-2008

READING MATERIAL

  • One Image – 17 Amazing Interpretations
    CameraPorn
    Results from a photo editing project similar to the one we ran on Epic Edits. 17 people give their very artistic interpretation of one image.
  • Replacing Skies or What Mood Today
    My Camera World
    It’s pretty amazing what a difference a new sky can make in your photos!
  • Street Tips
    The Meditation of Life
    Good solid street photography tips that talk about candids, fair game, knowing your equipment, expecting the unexpected, and the general nature of street photography.
  • 9 Pet Photography Tips
    digital Photography School
    Antoine gives us 9 great tips for improving our pet photos.
  • Reading Histograms
    SDuffyPhotography.blog
    A guide to reading a histogram and using that knowledge to take better photos.
  • Photowalking Tips
    SDuffyPhotography.blog
    Going on your first photowalk? Don’t forget to take these things with you!
  • 80+ Photoshop Tools and Resources
    Mashable
    A great big giant list of Photoshop resources including filters, brushes, actions, plugins, tutorials, magazines, associations, and other resources.