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Initial Steps in Image Preparation

¹ Department of Radiology, Children's Hospital, 300 Longwood Ave., Boston, MA 02115.

Received April 15, 2002; accepted after revision May 15, 2002.

 
Address correspondence to G. A. Taylor.

Introduction

Top Introduction Convert Files from Color... Remove Patient Identification Resize the Image References

 
Electronic presentation methods have become more widely available, and many radiologists are in the process of converting their extensive collections of 35-mm slides into electronic files for importation into PowerPoint (Microsoft, Redmond, WA). Several methods can be used for transferring analog images into your computer, including digital cameras, dedicated slide scanners, and flatbed scanners [1]. Although each method has its advantages and disadvantages, all have one thing in common: the quality of the digital image is never as good as that of the original slide. Over the past 7 years, I have used Photoshop (Adobe Systems, Mountain View, CA) extensively to prepare both professional and personal images for electronic presentations and publication [2]. In this series of articles, I will discuss methods available in Photoshop to repair and restore digital image files in preparation for importation into PowerPoint.

In this article, the first in the series, I focus on the basic steps that I have found to be helpful for the initial preparation of the electronic images. In subsequent articles, I will discuss how to restore image contrast, remove dust and scratches, adjust color, sharpen focus, and correct for photographic parallax. This information is intended to help users restore images to the original clarity and contrast, not intentionally distort or enhance medical images.

Convert Files from Color to Gray-Scale

Top Introduction Convert Files from Color... Remove Patient Identification Resize the Image References

 
Most, if not all, digital image file formats (DICOM [Digital Imaging and COmmunications in Medicine] equipment, digital cameras, slide scanners, or flatbed scanners) save images as RGB (red, green, blue) files. The resulting image is composed of three separate channels, each channel containing information about the red, green, or blue components of the image. Converting RGB files to gray-scale removes the color from the image without diminution in quality and can be used to remove color cast from a digitally scanned or photographed image. The resulting image file is approximately 60% smaller than the original RGB file.

The gray-scale option can be activated by selecting "Image" from the Photoshop menu. When "Image" is selected, a pull-down menu appears. From the pull-down menu, select "Mode" and then "Grayscale" (Fig. 1). I convert files from the RGB format to gray-scale first so that subsequent changes to the image are made to the smaller gray-scale file and therefore require less time to complete.

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —Image from computer monitor shows left side of Photoshop (Adobe Systems, Mountain View, CA) menu. To convert color file to gray-scale file, select "Image" option. From pull-down menu, select "Mode" and from that menu, click "Grayscale."

Remove Patient Identification

Top Introduction Convert Files from Color... Remove Patient Identification Resize the Image References

 
Unnecessary information, such as patient identification, can be removed by cropping the image. Before cropping, ensure that none of the marks outside the area of interest are needed. In the example provided (Fig. 2A), I wanted to include the word coronal in the cropped image, but this word appeared outside the area of interest. To move "CORONAL" into the area of interest, I clicked on the "Rectangular Marquee Tool" button that appears on the toolbar or "toolbox." Using this tool, I used the mouse to draw a rectangle around "CORONAL." Next, I selected the "Move" tool (cross with four arrows located just to the right of the "Rectangular Marquee Tool") from the toolbox; clicked the area I wanted to move; and moved the mouse so that the rectangle I had drawn was located in the area of interest—in this example, in the center at the bottom of the image. White space appeared where the word coronal had originally been, but this space will no longer be visible once I crop the image.

View larger version (109K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —Coronal sonogram of male neonate with postinfectious hydrocephalus. I modified this image in Photoshop (Adobe Systems, Mountain View, CA) for importation into PowerPoint (Microsoft, Redmond, WA). Original sonogram was obtained with digital camera that saved file in color format (RGB [red, green, blue] file). I scanned original image, which measured 1024 x 741 pixels, at resolution of 72 pixels per inch. In this image from computer monitor (screen shot), "Rectangular Marquee Tool" has been selected from toolbar or "toolbox," shown at left of sonogram. This tool was used to draw a rectangle around the area that I wanted to move into the area of interest—in this example, the word "CORONAL."

The image can be cropped by selecting the "Crop" tool from the toolbox (Fig. 2B) and drawing a rectangle around the part of the image that you would like to keep. The "Crop" option is activated by clicking on "Image" from the Photoshop menu and selecting "Crop" from the pull-down menu.

View larger version (114K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —Coronal sonogram of male neonate with postinfectious hydrocephalus. I modified this image in Photoshop (Adobe Systems, Mountain View, CA) for importation into PowerPoint (Microsoft, Redmond, WA). Original sonogram was obtained with digital camera that saved file in color format (RGB [red, green, blue] file). I scanned original image, which measured 1024 x 741 pixels, at resolution of 72 pixels per inch. In this screen shot, "Move Tool (V)" has been selected from toolbox, shown to left of sonogram. This tool was used to position word "CORONAL" in area of interest. White space represents area where "CORONAL" originally appeared. Cropping tool (arrow) was used to select image area that should remain in image, thus excluding white space and unnecessary words and numbers.

Many times, fragments of words or numbers still remain after the image has been cropped (Fig. 2B). To remove these markings, select the "Eye Dropper" tool from the toolbox, place the cursor over the background of the image, and click. This tool will sample the background color and set the background color as the foreground color on the toolbox. Select the "Paintbrush" tool, and move the cursor over the markings to "paint" the background with the foreground color (Fig. 2C). This tool is particularly useful when working with an image with a background that is not completely black.

View larger version (154K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C. —Coronal sonogram of male neonate with postinfectious hydrocephalus. I modified this image in Photoshop (Adobe Systems, Mountain View, CA) for importation into PowerPoint (Microsoft, Redmond, WA). Original sonogram was obtained with digital camera that saved file in color format (RGB [red, green, blue] file). I scanned original image, which measured 1024 x 741 pixels, at resolution of 72 pixels per inch. Screen shot shows "Paintbrush" tool in toolbox at left of cropped image. This tool can be used to eliminate unwanted words and numbers from image.

Resize the Image

Top Introduction Convert Files from Color... Remove Patient Identification Resize the Image References

 
Once the image is cropped to include only the needed elements, the image can be resized to optimize it for importation into PowerPoint. At the present time, most good-quality LCD projectors can display images consisting of a matrix of 1024 x 768 pixels (horizontal x vertical) [3]. The size of the image can be altered by selecting "Image Size" from the "Image" menu. When the "Image Size" dialogue box appears, select "100 pixels per inch" for the resolution under document size. In the upper part of the box, select 1000 pixels for the width. The height will default to a value that is proportional to the width. It is important to input these values in the order given because if the image dimensions are set before resolution is set, Photoshop may modify the settings for image resolution, resulting in an undersized image. Although other size combinations may also work well, I have found these settings to yield excellent results once the image has been imported into PowerPoint.

The resulting image has been cropped, and the patient identification has been removed (Fig. 2D). After conversion from color to gray-scale, cropping, and resizing, the file has decreased in size from 2.1 MB to 892 KB with no visible change in image resolution. However, the image still requires modifications before it is ready for presentation. In the next article in this series, I will describe methods that can be used to improve image contrast.

View larger version (156K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2D. —Coronal sonogram of male neonate with postinfectious hydrocephalus. I modified this image in Photoshop (Adobe Systems, Mountain View, CA) for importation into PowerPoint (Microsoft, Redmond, WA). Original sonogram was obtained with digital camera that saved file in color format (RGB [red, green, blue] file). I scanned original image, which measured 1024 x 741 pixels, at resolution of 72 pixels per inch. Modified and cropped sonogram has clear black background.

References

Top Introduction Convert Files from Color... Remove Patient Identification Resize the Image References

 

1. Schreibman KL. Hello, and two great tricks. AJR 2001;177:1017 -1018[Free Full Text]
2. Taylor GA. Swiss poppies. AJR 2002;178:730[Free Full Text]
3. Schreibman KL. Getting images into PowerPoint. AJR 2001;177:1271 -1272[Free Full Text]

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