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 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!

How to drill holes for cam lock connectors

Description
Discover the spacing and sizes of the holes in order to use cam lock connectors in your next project. Cam connectors provide a clean and secure, but easy to disassemble, joint for boards. In this video, I provide the drill bit sizes and hole spacing for commonly found cam locks.

For a written transcript, go to How to drill holes for cam lock connectors

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

Transcript

Want to learn how to drill the holes to use cam locks? I'll show how here today at the House of Hacks.

[Intro]

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

On a recent desk project I thought it'd be interesting to use cam locks for part of the assembly. It was in a couple areas where I didn't need huge amounts of strength and I wanted clean lines and easy disassembly. Cam locks seemed like a good solution.

If you're not familiar with them, cam lock connectors are a two part fastener that looks like this. They're used to connect two flat pieces together at a 90 degree angle. Things like the sides of book cases, or, in my case, a side support to a table top. There is a post that screws into the flat side of the first surface and slides into a hole on the end of the second surface. A cam lock slides into a hole in the surface of the second piece and locks onto the top of the post, pulling the joint together as the cam locks into place.

I have only seen them used in pre-cut furniture that's designed for home assembly, but I knew I could get them at my local home center. So I went down and picked some up. I did the next logical thing and searched around the internet to find out the hole pattern. Obviously I knew I needed several holes. I just didn't know the spacing and the sizes. Surprisingly, I didn't find anything on the internet. So I sat down to figure it out.

The home center had two types of posts: one had wood screw threads and the other had machine screw threads. I used the ones designed for wood. Both thread types came in only one size and it seemed about the same as all the other's I've seen in furniture kits. I don't know if the connectors come in different sizes or if there's pretty much only one standard. In any case, the bags for the ones I had were marked with "M6 x 45.5" for the connector bolts and "15mm x 16mm" for the cam connector. The details I present here are for these sizes.

All my bits are in imperial measurements, but the tolerances are close enough they worked just fine in spite of the metric hardware. I used a drill press for all my holes to help ensure straight holes and a good fit. If you don't use a drill press, do your best to get the holes as straight as possible.

For this project, three bits are needed: 3/16" and 5/16" in a twist or brad pointed bit and a 5/8" Forstner bit.

Use the 3/16" bit to drill holes for the posts to screw into. The depth isn't terribly important as long as it's deep enough for the post to screw in securely up to the shoulder of the thread. I found 7/16" deep worked well.

Before putting the posts into the hole, I transferred a mark to the other piece. It is fairly critical to get these holes correctly aligned as the post has to go into both of them. I didn't have any dowel centers small enough so I found a self-tapping screw in the surplus screw box with an outside thread diameter the same as my hole size. I cut it to a little over 1/2" long and set it in the hole, pointy side up. I used it to mark the center of the matching hole in the other wood. Then the post could be screwed in.

Next I drilled the holes in the end piece using the 5/16" bit. The holes need to be a bit over 1" deep. Again the depth isn't critical as long as it's long enough to go into the area where the third hole will be drilled.

Finally I drilled the hole in the side for the cam nut. Here I used the 5/8" Forstner bit. This hole is the most critical of the three. The center positioning needs to be pretty precise for the cam to engage properly. Its center is the same as the one on the edge and it's 1-5/16" from the edge. This puts the edge of the hole right underneath the top of the post. If it's too far from the edge, the cam won't engage and if it's too close to the edge the cam won't tighten against the wood.

Its depth will vary depending on the thickness of the material and where the post is relative to the surface. It needs to be about 4mm deeper than the distance the centerline of the post's hole is from the edge.

Once the holes are all drilled it's ready for assembly. The post is screwed into the first piece. Make sure to get it in straight and don't over tighten it, but get it snugged up to the shoulder. Now, the two parts just slide together. Finally, the cam is put in with the open side towards the top of the post and given a 180 degree turn with a screwdriver. If everything is done properly, it should lock down tight.

I'd recommend getting two pieces of scrap material to practice on. Once you've done it a time or two, it's easier to proceed with confidence on the main project pieces.

I'm pretty pleased with the way this worked. It took a bit to drill all the holes but it provides a nice clean joint that's secure and easy to take apart for storage or moving.

Thanks for watching and until next time, go make something. It doesn't have to be perfect, just have fun!