Category Archives: Media Lab

Image Histograms: What are they, and why are they important for digital images?


Image histograms are ubiquitous to digital images. You’ve probably seen them on your camera or any photo editing software. In this tutorial, I will be showing screen shots of image histograms from Adobe Photoshop

How do I find the image histogram in Photoshop?
To find the histogram that shows the various RGB colors, go to Window (top navigation bar) > Histogram
To find the histogram that shows the various brightness values of the colors, go to Image>Adjustments>Levels
**I will do a tutorial following this one that describes how to use Levels**


What is an image histogram?

Every color in a digital image has a brightness value ranging from 0 (black) to 255 (white).
An image histogram is a histogram of brightness values of every pixel in an image

Tones and Tonal Ranges

The tonal range is the region of the histogram were most of the brightness values are present.

This is a standard histogram of brightness values
This is a color histogram

What can an image histogram tell you about your image?

Lighting: is my image High Key or Low Key?

High Key Image: an image in which most of the tones are in highlights

Notice how most of the pixels are found in the highlight region of the histogram

Low Key Image: an image in which most of the tones are in shadowsImage
Notice how the pixels are mostly found in the shade region of the histograms

Overexposure of image: is my image overexposed?

An overexposed, aka clipped, image may have regions that are overexposed to the point that they are solid white and no detail can be seen.
Notice how the top left corner of this image is clipped.


This image’s histogram will show that the brightness values for some pixels are pushed to the very edge of the chart:

Breadth of Tonal Range: How many tones are in my image?

An image that has a broad tonal range will have a high pixel count on the far left and far right side of the histogram.



An image that has a narrow tonal range will have a high pixel count in one region.

Most of the colors in the picture are a light yellow or pink.. this is why the histograms have only 2 main peaks.
Notice that this picture also has high-key lighting

Amount of contrast in image: How much contrast is in my image?

A histogram with a broad distribution of brightness values also tells you that there is high contrast in the image.


On the other hand, a histogram with a narrow distribution of brightness values also tells you that there is low contrast in the image.
Notice that this image also has low-key lighting.

I hope this tutorial was useful to you!
Now that you have knowledge of how to read an image histogram,

learn how to manipulate the histogram by using Levels in my next tutorial!


How to color a black and white photo using Photoshop

In this tutorial I will show you how to color in a black and white photo using Adobe Photoshop

Here is an example of an old wedding picture I colored in for someone:


You can also create a funky image like this one:


WATCH THE TUTORIAL HERE (it’s 5 minutes long)


Don’t have 5 minutes?
Here are the basic steps:

1. Open image
The background layer is the black and white image that you’ll be coloring. Leave this layer alone

2. Create a new Layer

3. Change the mode of the layer from Normal mode to Color mode
To access this option, go to the Layers PANEL and look for the drop-down menu that says Normal.
Find Color in this drop-down menu and click on it to change the mode

4. Select a Color
The color you select is what it will look like when you brush it over a dark, almost-black shade

5. Use the Brush tool (B) to paint in the Color Layer you’ve created
Made a mistake and painted over something you didn’t want to? Simply use the Eraser Tool (E)

6. Continue painting until you’re done!

7. Save as a Photoshop document (.psd) in case you want to edit your color layers

8. For sharing, you’ll want to also save a FLATTENED copy of the image as a .jpg or .png or .gif, etc
Merge all the layers into 1 layer by selecting Layer in the navigation bar (up top) and go to Flatten Image
Save this file

* Create new layers for each color, or segment of the photo
* To layer colors, create overlapping Color Layers and then adjust the Opacity of the top Layer
* Name your layers to avoid confusion!
* To make one piece of an image pop, only color in the aspect you want to highlight and leave the rest black and white!

Creating a 3-D Animation of a 3-D SketchUp Model

After you’ve created a 3-D model in SketchUp, maybe you want to show it off or use it as part of a presentation. By creating a 3-D animation, you can display different aspects (angles, zoom levels, etc) of your masterpiece! Here’s a link to an example:

Animation works by SketchUp smoothly connecting arbitrarily selected “scenes” of your 3-D model:

  1. Make sure that certain settings are in place:
    Window > Model Info > Animation

    • Check off the box that says “Enable Scene Transitions”
    • Transition Time: speed up or slow down your
      animation transitions BETWEEN scenes
    • Slide Delay Time: amount of time the animation will PAUSE ON EACH SCENE before moving onto the next
  2. Position your view in the way that you want people to see it
    Use the Orbit, Pan, and Zoom tool to rotate, nudge, and zoom the view, respectively
  3. Go to View > Animation > Add Scene
    Notice that each time you add a scene, a button that says “Scene #“ appears. Clicking between these buttons will show you how SketchUp will smoothly transition between scenes.
  4. Repeat steps 2 and 3 until you have finished adding all the desired scenes
  5. After all your scenes have been created, click
    File > Export > Animation
  6. Save as > Format:

    • a Quicktime Movie (if on Mac)
    • an AVI (if on Windows)
  7. Next to Format, you can adjust the following Options:

    • Format
    • Width and Height
    • Frame Rate: in frames per second
    • Anti-Alias: Selecting this will double the time it takes to export, but the edges will come out nicer in the final movie
    • Transparent Background (the example selected this option)
  8. When you’re done selecting your options, click Export!

Using the Vinyl Cutter

The Vinyl Cutter in the media lab can be used to make simple and complex decals that can be affixed to most surfaces!

Before using the cutter, you’ll want to make sure of a few things:
1. Make sure that the vinyl is not too taut: it should look something like this

2. Make sure the vinyl is sticking out past the cutting area a few inches. This can be achieved by manipulating the blue POSITION arrows on the cutter

Now, you are ready to prepare your image using Adobe Illustrator
1. Open Adobe Illustrator and create your image.
If you want to use an already-made image, select the image and click on “Image Trace” in the top bar. After clicking Image Trace, the button will change to “Expand”. Click on Expand.
After creating your image, go to File > Cutting Master 2 > Cut/PlotImage

2. Then, this window will pop up. If your graphic isn’t already in the lower right corner, place it there by clicking and dragging in the preview area. Cutting Master 2 is able to detect the size of the vinyl as well as the placement of the cutters, so you generally don’t need to adjust the size and settings options

3. When you’re ready to cut, press Send.
4. When the vinyl is cut, you have to use a razor or scissors to cut the vinyl away from the cutter.
5. Remove the vinyl surrounding your cut image.
photo (5)
photo (6)

6. Get tape (ask a Media Lab monitor for tape) and place the adhesive side onto the color side of the vinyl. Rub it down vigorously, especially over your cut area!! You can use a card to really press down on the tape. This is important!
photo (7)
7. Remove the tape slowly. It helps to pull straight up rather than at an angle
photo (8)
8. Now, you’re ready to affix it onto a surface!
photo (9)
Place it on, vigorously rub, and slowly remove.

Remember, you can always ask a Media Lab Monitor for help!

Apple Blossoms Emerge

It took until mid-May this year for the crab apple tree outside the Media Lab to blossom, and our time lapse camera was ready. This video shows two-hour windows of time from subsequent days, racing forward from winter to spring, before lingering for several days as the tree finally blooms. Watch for the limbs to droop at 1:33 as a passing shower weighs them down.

About to Bloom

We’ve been watching the crab apple tree outside the window of the Media Lab for months now and it’s finally putting out some buds! In past years this tree has bloomed in mid-April, but the cold spring has delayed it. When it (finally) blooms we’ll post the time lapse video.