How to use histograms in Photoshop

Description

Histograms can be found in Photoshop for use in post-processing, not only on the back of our cameras when making the exposure. In this final episode of the Histogram series, Harley shows the different places histograms show up and what they represent within the image.

Other Histogram videos

Other Photography videos

For a written transcript, go to How to use histograms in Photoshop

Music under Creative Commons License By Attribution 3.0.
Intro/Exit: "Hot Swing"
by Kevin MacLeod at Incompetech

Sound effect: living-room-light-switch by alienxxx at FreeSound

Transcript

Histograms are an important tool when making an image in-camera. They also have their use during post-processing. In this episode of House of Hacks, I talk about how they work in Adobe’s Photoshop.

Hi Makers, Builders and Photographers. Harley here.

This is one in a series of videos about understanding and using the histogram. The others can be found in this playlist. I also have a playlist of other topics related to photography.

Today, we'll look at histograms in Photoshop. In this application, histograms tell us the same information as they do on the back of the camera but instead of just one histogram, Photoshop has several because of the different ways to view the image.

First off, if the histogram isn't visible, go to the Windows menu and select Histogram or you can click this icon.

By default it shows a little view like this. Click on this option drop down and select "All channels view" to see multiple histograms, one for each channel.

In many images all the channels will be very similar. But in some instances they might be quite different.

The split channels can be useful in situations where one color is predominant in your image. They help you see how adjustments to the image impact each color to help you know when one channel might start clipping, losing detail in the final image.

There's also this combo box that controls what is displayed in the top histogram. Personally, I like to show luminosity.

These histograms show the information for the image with all the adjustment layers applied. It’s the final histogram for the processed image.

As you turn adjustments on and off, you can see the histograms change accordingly.

Histograms also show up in some adjustment layers such as levels and curves.

The histograms that show in adjustments are the histogram for the image as that layer sees it, taking into consideration the original image and any layers below the current layer. This means adjustment layers above and below the current layer may have different histograms than the current layer.

As an example, this levels adjustment layer has a histogram for the original image.

If we make some adjustments and then add a curves adjustment above it, the curves layer shows a histogram based on the changes made by the levels adjustments.

If we make some adjustments on the curves layer, we can see the main histogram shows the results.

Also, if we make adjustments in a particular color channel, we can see how those changes impact that channel in the global histogram view.

If our adjustments are too extreme, we can see in the channel’s histogram that we start to lose details in this particular channel without the typical clipping showing in the main histogram curve.

In conclusion, I’d love to hear in the comments below about your experiences with the histogram, particularly during post-processing.

If this is your first time here at House of Hacks: Welcome. I’m glad you’re here. We’d love to have you subscribe. Through this channel I hope to inspire, educate and inform makers in their creative endeavors. Usually this involves various physical media like wood, metal, electronics, photographs and other similar materials. Thanks for joining me on our creative journey. So subscribe and I’ll see you again in the next video.

Now, go make something. It doesn’t have to be perfect, just have fun!

How to quickly isolate a subject on white using the histogram

Description

The histogram is a powerful tool for the photographer. In this tutorial, Harley shows how to use this feature found on most cameras to quickly and easily setup lighting to isolate a subject on a pure white background. Properly done, a subject isolated on a white background is simple to cut out to composite into another image.

Histogram playlist
Photography playlist

Special thanks to my wife Diane for being the test model and my buddy Rich at Studio 020 for letting me use one of the rooms.

Overhead diagram created by the Online Lighting Diagram Creator.

Music under Creative Commons License By Attribution 3.0.
Intro/Exit: "Hot Swing" by Kevin MacLeod at http://incompetech.com
Incidental: "Sweeter Vermouth" by Kevin MacLeod at http://incompetech.com
Sound effect: living-room-light-switch by alienxxx at http://freesound.org

Transcript

Today at the House of Hacks, I’m going to talk about an impulse purchase I made several years ago that’s turned out to be one of the most used tools in my workshop.

[Intro]

Hi Makers, Builders and Do-it-yourselfers. Harley here.

A number of years ago I had an Amazon order that I needed to fill out to get free shipping on. So I ended up purchasing one of these inexpensive digital calipers. It was just an impulse purchase. I figured it’s cheap enough that if I never use it or I don’t like it, no great loss.

As it turned out, this little thing has… I use it on almost every project. It measures up to six inches and anything under six inches I’m pretty much using this to measure with.

It’s just really, really handy.

There’s a whole bunch of these on Amazon. This one I picked up for around 37 or so dollars. It’s one of the more expensive ones. I’ve seen them on, just searching before this video, I was searching and saw them for under ten dollars. They’re so inexpensive, I’ve seen people buy them new, cut them up to use the measuring device in things like jigs and things like that. So, they’re really inexpensive for whatever purpose you want to use them for. Like I said, I use them for almost every project whenever I need to measure things.

They’re great for measuring outside measurements using these big calipers. Using the smaller inside calipers you can measure inside measurements. And on the end you can measure depth.

They have a zero button on them so you can zero it out. You either close the jaws, zero it out and then you get an accurate measurement. Or, you can use it to get the difference between two measurements. Take one measurement, zero it out, take another measurement and that gives you the difference between the two sizes. That can be really handy.

And it’s also good for transferring distances. You can use the ends, they are sharp so you can scribe a little bit. Measure one thing and then use it to scribe.

It does have an on/off switch which doesn’t really work all that well. All it does is turn on and off the LCD display which really doesn’t draw much power. If you’re going to leave these sitting around unused for a week, you really should take the battery out and that’ll give you much longer battery life on it.

That said, the batteries are 357 button cells. Little things that you can get at Walmart, Target, places like that for a couple bucks a piece. They’re much cheaper on Amazon if you buy them in bulk. So I recommend buying them on Amazon because I think they’re less than a dollar a piece whereas the cheapest I’ve found locally is like a buck fifty, two bucks, something like that.

They have a units switch that switches between millimeters, inches as decimal and inches as fractions. So that can be handy depending on what it is you’re measuring and you’re comparing it to other things and what units you’re most comfortable with.

The device also came with a plastic carrying case. Just kind of inexpensive, but it does protect it. And inside it has a foam cutout for the calipers and two places for batteries. So if you’re carrying it around, that kind of protects it and keeps it from getting beat up.

A really, really handy device. I really recommend getting one.

So that’s it for today. I’ll leave a link down in the description for an affiliate link if you’re interested in helping support the channel.

Until next time, go make something. Perfection’s not required. Fun is!

How to use the histogram to reduce noise in your photos

Description

Noise in photos can be a problem at higher ISOs, particularly in older cameras. In the episode, Harley talks about how shooting to the right of the histogram and then adjusting the exposure in post processing can help minimize noise. Topics covered include the reason this technique works, how to make the image in camera and how to adjust it in post-processing.

Special thanks to Rich Legg at Studio o2o for letting me use his remodeled lobby for the example shots. Studio o2o has great photography studios available for rent in the greater Salt Lake City, UT area. See their web page for more details.

Histogram playlist

For a written transcript, go to How to use the histogram to reduce noise in your photos

Music under Creative Commons License By Attribution 3.0.
Intro/Exit: "Hot Swing" by Kevin MacLeod at http://incompetech.com
Sound effect: living-room-light-switch by alienxxx at http://freesound.org

Transcript

Perhaps you’ve heard you should "shoot to the right."

What does this really mean?

And why should you think about doing it?

I'll try to answer these questions today at the House of Hacks.

[Music]

Hi Makers, Builders and Photographers. Harley here.

To "shoot to the right" refers to the right side of the histogram.

If you're unfamiliar with the histogram and how to use it, I have other episodes in this playlist where I talk about these topics.

In general, with an average scene, a proper exposure looks something like this one on the histogram.

The black side starts small, it increases through the grays and then drops off again approaching white.

The camera’s computer will try to make every scene fit somewhere in this curve.

The problem comes when you have large dark areas in your images.

These areas are more susceptible to having problems with noise coming from the sensor.

Here's an example of noise. See these odd blotches in what should be a smooth dark area?

Noise actually happens over the whole image, but it's mainly visible in the dark areas. Let’s see why.

Noise causes small random changes in the value the sensor detects for a given pixel.

Because the changes are small, and dark areas have small values, the noise is a greater percentage of the actual image data in the dark areas as compared to the lighter areas.

Just for the sake of argument, let’s say the noise is variations between plus and minus 10 values from the actual, ideal image pixel value.

Let’s say this area of the image ideally should have values around 20. When we add noise, a swing of 10 represents a change of 50% from ideal of 20.

If you have a two adjacent pixels that both ideally should be 20 but one has +10 noise and the other as -10 noise you end up with a 100% difference from the ideal between the two pixels.

Conversely, if we look at a bright area of the image where the values are around 200 a change of 10 represents only 5%, a much smaller relative change.

And so, because the noise represents a large percentage of the dark area’s values but only a small percentage in the bright area, it’s much more noticeable in those darker areas.

So what does this mean for the topic of “shoot to the right?"

The idea is that you should adjust your exposure compensation to shift the "ideal" exposure for gray to the right as much as possible but without clipping.

If you're in an automatic mode, you do this using the exposure compensation feature of your camera.

And if you're in manual mode, just simply adjust one or more legs of the exposure triangle to get what you want.

Use the histogram to determine when you have arrived at the correct point.

First, take a test image at what the camera says is the "correct" exposure and look at the histogram to see how much room you have.

Then dial the exposure compensation up to increase the exposure. The idea is to move the peak of the image to the right of the histogram.

Take another test image. And then repeat this process until the image is as bright as possible without clipping.

When you do this, the dark areas of the image move up into brighter areas where noise isn’t so much of an issue.

The problem now though is the dark areas will no longer be their proper dark color, they will be a washed-out grey. And the medium areas will be much too bright.

It just simply won't look right, but this can be fixed in post-processing.

Here's our image in Photoshop, a bit too bright since it was shot to the right. There are several ways of adjusting this.

The curves adjustment layer can be used to move that area that's too far to the right back into the center.

Just drag the black point at the bottom left of the curve over to the right but don't go so far that you start clipping your blacks.

You may also need to adjust the curve down to darken the overall image.

Another option is to use a levels adjustment layer to move the black point to the right, causing the overall exposure to be lowered and evening out the curve.

A third option is to use an exposure layer to simply lower the exposure.

Regardless of the method used, since the dark part of the image was captured outside the noise range, when the image is adjusted, the area the noise is in will be crushed and made much smaller, resulting in significantly less noise in the dark areas.

Here's the example scene shot with the exposure as the camera decides it should be.

And here it is shot to the right.

Finally, here's the shot to the right example with post processing.

Notice the difference in noise in the dark areas.

In conclusion, I’d love to hear in the comments if you have any opinions on using this technique. I know in some places it’s a bit controversial and in newer cameras noise is much less of a problem.

If this is your first time here at House of Hacks: Welcome. I’m glad you’re here. We’d love to have you subscribe.

Through these videos I hope to inspire, educate and inform makers in their creative endeavors.

Usually this involves various physical media like wood, metal, electronics, photographs and other similar types of materials.

Thanks for joining me on our creative journey. So subscribe and I’ll see you again in the next video.

Now, go make something. It doesn’t have to be perfect, just have fun!

How to get a perfect exposure using the histogram

Description

This is the second in a series where Harley talks about histograms as they’re used in photography. Having problems getting a good exposure based on the preview image of your camera? In this episode we look at how to use the histogram to get the exposure you want for your images.

This episode looks at exposure as it relates to the histogram: what is "proper" exposure, how different types of images impact exposure and the histogram and finally how to see exposure problems on the histogram and what to do to correct them.

Previous video: How to easily read a camera's histogram
Playlist of histogram related videos.

For a written transcript, go to go to How to get a perfect exposure using the histogram

Music under Creative Commons License By Attribution 3.0.
Intro/Exit: "Hot Swing" by Kevin MacLeod at http://incompetech.com
Light switch effect: http://freesound.org/people/AlienXXX/sounds/151347/

Transcript

Struggling to get the exposure you want? Today at the House of Hacks we’ll look at how you can use your camera’s histogram to get the perfect exposure.

Hi Makers, Builders and Photographers. Harley here.

The histogram is an important tool to understand the actual exposure of an image. When working with people in classes and workshops, I've noticed many of them look at the picture on the back of their camera trying to evaluate the exposure but don't have the histogram turned on. The problem is the image displayed on the back of the screen does not represent the actual exposure saved in the raw file. This preview is filtered based on several camera settings such as picture mode and white balance. Also, that screen is tiny and uncalibrated. It's really only a rough approximation of the actual image. Now don't get me wrong, the preview is a valuable tool; it’s great to see the overall composition. However, it's nearly useless to evaluate the exposure.

In this previous video, I explained what all the information on a histogram means. Today we'll look at the exposure as it relates to the histogram: what is "proper" exposure, how different types of images impact exposure and the histogram and finally how to see exposure problems on the histogram and what to do to correct them.

Somewhere in the history of photography, someone decided a "proper" exposure had a histogram that looks like this. It assumes that on average the majority of the luminance information is in the center of the image. Another way of saying this is that 50% gray will make up most of the image.

So, the exposure computers in cameras look for a peak in the image and try to adjust camera settings to put the peak in the center of the histogram. And this works well if you have an evenly lit, average subject. In an image like this, this rule works.

But this isn't necessarily valid for images that fall outside of average. And for artistic purposes, it’s not at all unusual to want something intentionally different.

For example, in low-key images, where a large percentage of the image is dark, this peak should be skewed to the dark side of the histogram on the left. But the exposure computer will try to push it to the center, making what should be dark, a washed out grey. This isn’t necessarily a bad thing, and in a future video I’ll talk about why you might want to intentionally do this. However, if you try to get the exposure correct right out of the camera, it doesn't give you what you really want.

Conversely, in high-key images, where a large percentage of the image is bright, the histogram should have the peak skewed to the right. But again, the computer will try to push it to the center, making what should be bright look dingy. Frequently you’ll encounter this problem shooting bright scenes outdoors, like at the beach or in the snow.

Unless the overall dynamic range of the scene is greater than your camera, generally both these problems can be fixed in post-production. However, both these problems are easily detected and corrected in-camera using the histogram. If you’re aware of the conditions you're shooting in and the look you're trying to achieve, you can know where the peak is supposed to be. Knowing where you want it, you can look at the histogram to know if it's in the correct spot or not.

If you find it’s not where you want it, and you’re using an automatic mode, use the exposure compensation setting on your camera. It allows you to tell the camera to adjust where the peak rests relative to center. By setting it to the plus side, you're telling it to move the peak to the right to brighten the image, or from the camera's perspective, you want to overexpose the image. By setting it to the minus side, you're telling it to move the peak to the left to darken the image, or, again from the camera's perspective, to underexpose the image.

If you’re in manual mode, simply adjust one of your exposure settings, f/stop, shutter speed or ISO, to make your image brighter or darker. If you're using your camera's exposure meter, the computer’s “perfect” exposure will be with the indicator right in the middle. If the image with this exposure is too dark for your scene, adjust your settings to move the indicator to the right. Or if the image is too bright, just move the indicator to the left.

Once these adjustments are made, make another image and re-evaluate the histogram. Repeat this process until the peak is where you really want it.

A significant problem in digital photography, that wasn't so much an issue with film, is clipping. With digital imaging, once a part of the image gets to a certain brightness level, it can't go any higher and is simply cut off. Everything brighter than that level is set to that maximum. It's clipped off. This causes a loss of information. The same type of thing happens in the dark regions. There's a level that means "black" and once that level is reached, anything less than that is set to black.

Imagine a number line that's really big in both directions. This is reality. But a digital sensor can only capture a region of this infinite line that has 256 values. Anything less than 0 is treated as 0 and anything greater than 255 is treated as 255. The number line is just cut-off, chopped, or clipped. Within a certain range, using exposure controls and ND filters, you can adjust where on the line this camera defines the start and end points, but you can’t change the size of the window.

Fortunately, clipping is easily detected by the histogram. If you have a tall vertical line on the extreme left or right edge, that image was clipped. If you see this, and you know you shouldn't based on your subject, you need to adjust your exposure either up or down, depending on which side of histogram the problem lies. Some cameras will flash areas of an image that are over and underexposed.

Just keep in mind, there are some cases where this can be expected to happen. A landscape image with the sun in it, or something with specular highlights, will probably have a small amount of clipping. This is normal and to be expected since these are the brightest areas of the photo. But if it's a wedding dress or white shirt, that's definitely a bad thing because any clipping will result in a loss of detail in these areas.

In conclusion, I’d love to hear in the comments below about how much you’ve actually used the histogram in the past. And, if you have used it, how it’s helped you.

Here are two playlists. One has all my photography related videos and the other contains other histogram related videos.

If this is your first time here at House of Hacks: Welcome. I’m glad you’re here. We’d love to have you subscribe. Through these videos I hope to inspire, educate and inform makers in their creative endeavors. Usually this involves various physical media like wood, metal, electronics, photography and other similar materials. Thanks for joining me on our creative journey. So subscribe and I’ll see you again in the next video.

Now, go make something. It doesn’t have to be perfect, just have fun!

How to easily read a histogram

Description

The camera’s histogram can be intimidating if you don't understand it, but it's actually really simple. In the first of a short series, Harley introduces this powerful tool to facilitate photographers' quests for the perfect exposure.

For a written transcript, go to How to easily read a histogram

Music and sound effects under Creative Commons License By Attribution 3.0.
Intro/Exit: "Hot Swing" by Kevin MacLeod

Photo credits for Creative Commons license 2
Illusive Photography: Photo
Alessandro Valli: Photo

Sound effects credits for Creative Commons license 3
fasten: Slide projector
VlatkoBlazek: Mechanical Whirring
leosalom: Fire

Transcript

[Click]

Besides the basic controls for making an image, I find the histogram to be one of the most used features of my digital camera. Today at the House of Hacks I'm going to explain what it is and the meaning of what it shows.

[Music]

Occasionally I work with people in photography related teaching situations. Many times I've found individuals trying to evaluate an exposure based on the preview image on the back of their screen.

This is a really bad idea. Chimping is great to evaluate the composition and relative exposure but there are many factors that control how the image is displayed that make it a poor representation of the actual exposure.

The histogram is a powerful tool in the photographer's arsenal to evaluate an image for proper exposure. And it's one of the few features that can't be duplicated on a film camera.

The closest we can get in the film world is an exposure meter. But in the digital world, the histogram provides a whole lot more information. In this episode, my goal is to explain the basics of what the histogram is and the meaning of what it shows.

In future episodes I plan to show how to use it when making an image. They'll be added to this playlist when they're posted.

Simply, the histogram is a chart showing the various brightness levels of an image. The left side of the x-axis represents black and the right side represents white. The values in between are levels of gray from dark to light. The y-axis represents how much of the image is at each value on the x-axis.

Let's look at some simple examples. To make things a bit easier, let's visit an alternate universe.

[Finger snap]

In this world, things are much more pixelated with higher contrast and fewer colors so our histograms can be smaller. When the sun goes down everything goes to black and white and a couple shades of grey.

Here's a nighttime image. Let's construct a histogram for it. First, we'll draw the x- and y- axes.

Since our image only has four values, black, white, dark grey and light grey, the x-axis has four points.

First we count the number of black pixels. Then we draw a bar that high.

Then we count the number of dark grey pixels and draw a bar that high.

We continue the same process with light grey and white.

And there we have it. A histogram for this image.

Let's change the image a little... and see how it changes the histogram.

More grey in the image increases the grey column of the histogram and decreases the white side.

Here is the same scene during day... with it's histogram.

A color image can be treated as a black and white image, with many shades of grey.

In this case, the histogram just has more grey levels on the x-axix.

Let's look at a couple generated images to get an intuitive feel for how the image impacts the histogram.

Previously I've shown simplified histograms with just the number of items on the grey scale x-axis as there are in the image. From now on, the histograms will be configured to have 256 values on the x-axis from black to white.

This black and white image gives us two bars in just the black and white columns on the two edges.

This black and white image gives us the same histogram because the relative amount of black and white portions of the image are the same.

It doesn't matter how we divide this up, as long as we have the same number of black and white pixels, the histogram remains the same.

Similarly, if we have this black and white image with one-third of the image white and two-thirds black, we can see the black side is twice the size as the white because we have twice the number of black pixels.

And again, we can divide those pixels up anyway we want, but the histogram doesn't change.

Now let's look at this gradient image.

Its histogram is a straight light.

Does this surprise you?

If we look at the image, we have a black band and a white band and all these grey bands that are the same size. So the graph reflects this with a straight line.

If we move the black and white start points, then the histogram will have taller ends with a dip in the middle.

But if we move the black and white start points off the image, then the histogram will shorten on the ends and rise in the middle.

[Finger snap]

And the default histogram on your camera works exactly the same way. Each image is treated as black and white and then the histogram constructed from that.

I don't know about all cameras, but all my Canons have two types of histograms: luminance and RGB. The luminance histogram is a single chart that shows the combined luminance values for the overall image. The same thing as what we’ve been looking at here.

The RGB histograms work exactly the same way except there are three charts showing the intensity in each of the color channels.

The default is to show the luminance but it can e changed to the RGB histogram by changing a custom setting in the menus.

This can be useful in situations where you have colored lights or part of your image that is more predominant in one color than the others. In these cases, one channel might become overexposed but it won't be obvious in the luminance histogram. However, when you change to the RGB histogram it becomes quite obvious.

And that's how you read a histogram. The left side shows how much black you have and the right says how much white you have and everything in the middle indicates shade of grey.

In future episodes I plan to show how to use this information while making an image and what it means to shoot to the right. If you want to be notified when that, or any other maker related episodes, are released, hit the subscribe button.

Thanks for watching. If this helped you, I'd appreciate knowing about it with a "like." If you have any other questions or other comments, I'd love to hear them in the comment section below.

Until next time, go make something. It doesn't have to be perfect, just have fun!