This tutorial is about one aspect of photo retouching in Photoshop - using the Levels Adjustment to correct tonal values. The Levels Adjustment function in Photoshop can be used in a variety of ways. This tutorial explores just one way.
1. In the photo of the black bag below, the exposure looks pretty good at a glance, but because the color of this object is primarily black, it requires a little tweaking to reveal some of the detail. The Levels Adjustment will bring out the detail which is buried under the dark areas where it is difficult to see. On the right is a histogram of the image. In this tutorial, I am using Adobe® Photoshop CS. In this version the Histogram Palette is grouped with the Info and Navigator Palettes by default. The histogram is a graphic representation of the distribution of light and dark pixels. The horizontal axis represents the "darkness" of the pixels in the image - going from the darkest pixels on the left to the lightest pixels on the right. The vertical axis represents the number of pixels for each shade with the smallest number of pixels on the bottom to the largest number of pixels at the top. Please note the large clump of pixels on the left end of the histogram. This is an indication that this is a dark photo.
2. Now, if you had to lighten this image for print or for a web page, you may have a tendency to go straight for the "Brightness and Contrast" adjustment. Generally I will save Brightness and Contrast as my last adjustment - but not always. If you try to use Brightness and Contrast all by itself to do the job you will probably be disappointed in the results. Here's why... Go ahead and click Image > Adjustments > Brightness and Contrast (or Image > Adjust > Brightness and Contrast with older versions of Photoshop). Check the "Preview" checkbox and drag the Brightness slider to the right to lighten the image.
3. Now take a look at the result. You can see some more detail but the image is overexposed. It looks "washed out". Also, please note the histogram with the telltale blank area on the left side where there are no pixels represented in the dark end of the graph. This is a sure sign of an underexposed image. There were two mistakes here. Using Brightness and Contrast was only one of the mistakes. The other was using the Image > Adjustments command. You see, that command will permanently alter the pixels. Once you save and close the file, the data is gone and you can't get it back unless you have a backup copy of the image. Don't feel bad if you have done this. I messed up a whole bunch of images like this when I first began to do image editing.
4. Okay, let's re-open the file or click Edit > Undo, or File > Revert ... whatever it takes to get back the original image and this time we will use an Adjustment Layer. This will place a layer over the original pixels where we can make our adjustments. When we view the image we look down through this layer as if the adjustments were done to the pixels themselves. The difference is we can turn the visibility of the adjustment layer off so we don't see its effect on the pixels below it or we can throw the layer away and the pixels in the image will remain untouched. As a rule, I will always use an adjustment layer to preserve the original pixels in the image just in case I make a mistake. Click Layer > New Adjustment Layer (or Layer > New > Adjustment Layer for older versions of Photoshop). Give the layer a name or accept the default name it gives you and click the "OK" button.
5. You will see the Levels dialog box and you will also see a change in the Layers Palette. You can see the new adjustment layer over the image Background Layer (or regular Layer name if it isn't the Background Layer).
6. Now let's turn our attention to the Levels dialog box. As I mentioned earlier, you can use the Levels adjustment in a variety of ways. In this example, we will use the little dropper buttons in the lower right corner. Click the one on the left to set the black point.
7. Find the darkest area on the image and click the dropper once.
8. Next click the button on the right to set the white point.
9. Find the lightest area on the image and click the dropper once.
10. Finally, click the button in the middle to set the gray point.
11. Find an area with the most neutral midtones in the image and click the dropper once.
12. Next, we want to shift the midtones of the image to lighten them slightly. The center triangle at the bottom of the histogram is the gamma adjustment for the Input Levels. Dragging this triangle to the right will darken the midtones, while dragging it to the left will lighten the midtones.
13. Drag this triangle to the left just slightly. Make sure the Preview checkbox is checked so you can see the effect of this adjustment as you make it. After you make the adjustment, you will see a change in the center box of the Input Levels just above the histogram.
14. This is a view of the image after the Levels Adjustments. Also please note the histogram to the right, below and compare this with the first view of the histogram at the beginning of the tutorial before any adjustments were made. The tonal values for the pixels have been redistributed.
15. Below are screenshots of the image before and after the Levels Adjustments. More retouching can be done with this image but the levels Adjustment has made a big difference. You can see the detail and yet the tonal values are still in good balance. The image is neither overexposed or underexposed.
This is the second tutorial on using the Photoshop Levels Adjustment to correct tonal values. The Levels Adjustment function in Photoshop can be used in a number of ways. Like the previous tutorial, this example explores another way. This time we will make the Levels Adjustments by manually adjusting the Input Levels.
1. This photo is slightly underexposed. When you look at the histogram, you can see that the right side of the graph is nearly flat. There are almost no pixels on the "light" end of the graph. Please check the previous tutorial for an explanation of the Histogram Palette. Like the previous tutorial, we want to add an Adjustment Layer to make the Levels Adjustment. Click Layer > New Adjustment Layer (or Layer > New > Adjustment Layer for older versions of Photoshop). Give the layer a name or accept the default name it gives you and click the "OK" button.
2. Below is a Flash Video showing you how to make the Levels adjustment. The small white triangle on the right end of the bottom of the histogram is dragged towards the center of the graph. Make sure the Preview checkbox is checked so you can see the effect of the adjustment as you make it. Please notice that as you drag the white triangle to the left that the gray triangle in the center moves a proportional distance towards the left as well. After you have made the adjustment, click the "OK" button.
3. The result is a bit more exposure. The tonal values are more balanced. Also please note the histogram. The pixels have been redistributed.
4. In this next example. we will be making the opposite adjustment. The image is slightly underexposed...but not much. Please note that in the histogram, there are almost no pixels in the left side of the graph. Just like the previous example, add an Adjustment Layer to make the Levels Adjustment. Click Layer > New Adjustment Layer (or Layer > New > Adjustment Layer for older versions of Photoshop). Accept the default name it gives you and click the "OK" button.
5. Below is a Flash Video showing you how to make the Levels adjustment. The small black triangle on the left side of the histogram is dragged towards the center of the graph. Like the previous example, when you drag the triangle to the right that the gray triangle in the center moves a proportional distance towards the right as well. After you have made the adjustment, click the "OK" button.
6. The result is an image with a little more contrast. As in the previous example, you can see the redistribution of pixels in the histogram.
7. Below you can see the before and after shots of the image. The Photoshop Levels Adjustment adds just a little bit more contrast. You can see more detail in the lighter parts of the image than you could before the Levels Adjustment was made.
This is the third tutorial on using the Photoshop Levels Adjustment. Like the previous tutorial, this example explores another way to use the Levels Adjustment to correct tonal values. This time we will use the Auto Levels Adjustment feature then manually adjust the Input Levels to tweak the automatic adjustment. The "Auto" Levels Adjustment does not always yield a good result, but sometimes it is worth a try. Usually, when I do use it, I will use it in combination with a manual adjustment of some kind similar to this tutorial.
1. This photo is slightly underexposed. The Auto Levels Adjustment can be done two ways. One way is by clicking Image > Adjustments > Levels (or Image > Adjust> Levels with older versions of Photoshop). This way will permanently alter the pixels.
2. Like the previous tutorial, we want to add an Adjustment Layer to make the Levels Adjustment so the pixels will not be permanently altered. Click Layer > New Adjustment Layer (or Layer > New > Adjustment Layer for older versions of Photoshop). Give the layer a name or accept the default name it gives you and click the "OK" button.
3. Below is a Flash Video showing you how to make the Levels adjustment. First click the "Auto" button. After the automatic levels adjustment, the photo is still a little bit dark, so we want to shift the midtones of the image to lighten them slightly. Drag the small gray triangle in the center at the bottom of the histogram between the white and black triangle on either end. Drag this traingle to the left just slightly. Make sure the Preview checkbox is checked so you can see the effect of this adjustment as you make it. After you have made the adjustment, click the "OK" button.
3. After the Levels Adjustments you can see that the tonal values are more balanced. Again, the "Auto" Levels Adjustment does not always yield a good result. In my experience I rarely use it, but sometimes it produces miraculous results that I could not do in a million years with manual adjustments. It is definitely a good option to keep in mind when photo retouching with Photoshop.
Some people have asked me, "How do I get a chart from Excel into a Quark document?". There are a couple of ways to do this but the best way is to export the Excel graph as a PostScript® file, then open the PostScript file in Adobe® Illustrator® or other drawing program like Macromedia® FreeHand®, CorelDRAW® or Deneba Canvas™. Once opened in one of these programs, you can convert colors from RGB to CMYK or spot color so the colors will separate properly if the Quark document is intended for printed output. Then you can save the graphic as an EPS file and place this EPS file in the Quark document as a picture.
This tutorial is for QuarkXPress Windows®. Following are the step by step instructions:
1. Select the graph or chart in Microsoft® Excel.
Click thumbnail image for larger view
2. Click File > Print and choose a PostScript printer. If you don't have an actual PostScript printer connected to your computer, don't worry. You can setup a printer that prints to FILE. For more info on how to do this, please check this tutorial for Windows XP and this tutorial for Windows 98.
3. You will be prompted for a filename. Give it a .ps or .prn extension.
The file is saved to your drive.
4. Next, the PostScript® file has to be opened in a drawing program. In this case we will use Adobe® Illustrator®.
Click File > Open, then navigate to the PostScript file saved in the previous step.
Click thumbnail image for larger view
Illustrator will open the PostScript file for editing. If the graphic is to be output to print, then in this step you will convert colors from RGB to CMYK or spot color depending upon how the document will be printed. You will have to do this so the colors will separate properly.
5. When you have finished your edits, click File > Save As.
In the Save dialog, choose EPS from the "Save as type" drop down menu.
Click thumbnail image for larger view
6. Illustrator® will present you with the EPS Format Options dialog. In this case we will choose version 7 compatibility. In this case version 7 will suffice and it is widely supported so you shouldn't expect problems at your service provider. Note that you can also embed fonts in EPS files with Illustrator. I will usually check this option when it is available. More on fonts and EPS files here. Make sure to save it with a preview. More on saving EPS files with a preview here.
7. Illustrator wants to make sure you want to save in an earlier version...click OK.
8. The file is saved to your drive.
9. Now switch to QuarkXPress and open the document where you want to place the graphic. Create a picture box for the EPS file, then click Ctrl + E (or click File > Get Picture).
10. Navigate to the folder containing the EPS file saved in a previous step and select it.
11. The pie chart is placed in the Quark picture box where you can position it and scale it. You can scale it up or down with no loss of quality because it is a vector EPS file. More on the vector format here.
