Digital Imaging Institute for Science and Medicine

It Starts With The Histogram

2009-04-29T12:50:00.000-07:00

Understanding digital photography starts with the exposure. If you compare it to exposing film, it is more like transparency film than negative film. To get the best dynamic range from a digital exposure, you must expose it as bright as possible without over exposing the image. There is a fine line in finding that perfect place. Many photographers play it safe and stay on the lower side of the perfect exposure. Pro photographers know not to overexpose, but getting that perfect spot on the verge of overexposure is where the beauty lies in digital Imaging. To find that perfect place you must master the art of previsualization and reading of the histogram.

   In the days of film, we could always count on the Polaroid to double check the exposure. Learning to read the Polaroid exposure and evaluate the results to adjust the film exposure was very important if you want consistent results without bracketing all over the place to get the final image. The photo on the LCD viewer of our camera is not a modern day equivalent of the Polaroid. You must learn to look at the scene and understand where the exposure should be to create the perfect rendering of the image. Remember, there is no such thing as a good or bad histogram. There can only be a good or bad rendering of the file. Think of the histogram as a bar chart with 256 separate bars. How high any one bar rises depends how many times any pixel value appears in the image.

   When determining the proper exposure for the final 8 bit file, you will find that on a scale of 0-255, white with detail is at about 240-245. Above that, white will start to loose any true detail as it approaches pure white of 255. On the shadow side, black with detail lives at about 20-25. Below 20 and you start to loose you shadow detail. This does not mean you can't have a pure black of 0, or a pure white of 255 in you image. It just means you need to be aware of where these values fall to hold detail in the areas that really need it. Just remember to expose for the highlights, and process for the shadows.

   By shooting Raw files you will have incredible control over the tonal range of the image. Buy letting the camera process it’s Raw data into jpeg files, you lose all this control. You spend a lot of cash for these incredible cameras, and not want the best possible quality? That’s just plain crazy….

Finding the “Goodies” in Photoshop CS4

2009-04-09T19:01:00.000-07:00

As we move from earlier versions of Photoshop to new ones, we learn new tools and techniques to build on what we already know. Photoshop CS4 and CS4 Extended are no exception. Eventually, some of the older tools and filters will fade away as they make way for the newer streamlined workflows and effects. As we learn and get comfortable with the newer tools and interface, you my find that you sometimes miss the way you did a task in the past. I first noticed it in CS4 when I would stitch images together, I noticed there was a dialog box we had in earlier versions that was not there anymore that allowed individual control of the elements being stitched. I liked that extra step for complex compositing of images. After talking to the folks at Adobe, I found out that it was there and could be put back in…. It was there on my install disc all along with a bunch of other cool stuff that puts some the PS CS3 bells and whistles back into your PS CS4. These plug-ins can be found on your PS CS4 install disk in the English folder. Inside of that folder is a “Goodies” folder containing lots of fun stuff to put back in your PS CS4. Besides the Photomerge extension, there is the older version of the Photo Web Gallery. I like the new procedure through the Adobe Bridge CS4, but I also like the older Photoshop version of Web Gallery as well. In the Goodies folder you have the older Web gallery can install and access from both the Tools/Photoshop Menu in Bridge CS4, or the File/Automate Menu in Photoshop CS4. Other items you can install include the Extract Filter, the Pattern Maker and the Contact Sheet Plug-in. If you don’t have the install disc due to the original software being a downloaded version, you can find them on the Adobe Software Download site as well. You can’t just drag the whole thing into the PS CS4 Plug-in folder. There is an important read me file that comes with the plug-ins it that will tell you where to put each file. You really have to follow it to a letter. Directions are easy to follow for each plug-in. A few minutes of drag and droping files and you are ready to go….

Back from Boston!

2009-04-03T19:19:00.000-07:00

Welcome to the Digital Imaging Institute for Science and Medicine. This is our first post and we are very excited after conducting the first Photoshop for Medicine seminar at the Joslin Diabetes Center in Boston this past Saturday. Course evaluations were very positive, and we have already made improvements to the seminar content based on your feedback. Our goal is to have posts from different imaging specialties represented here to share with our growing membership. Our next seminar will be in Atlanta at the Emory Eye Center on April 18th and our latest updates will make the program even better for the attendees. As new members, we invite you to become followers of our blog. You can register through the “Followers” sign in on the right side panel. Our goal is to start a conversation within our community that will continue to grow as the organization does. Please share your thoughts and ideas with us. This is your organization. Jim and Mark

Photography by Helene Glassman/Imagery Photography.