MacOS provides a few different ways to do screen captures. My personal favorite is Grab, which is found in the Applications/Utilities folder. It lets me capture a selection, a window, or the whole screen without having to remember any magic key combinations. I keep it in the Dock for quick access.
Grab has one deficiency, though. It can save screenshots only as TIFF files. If Apple had to pick just one format, that’s hardly the most useful one. But there’s an easy workaround.
After you’ve got your screen shot, press Command-C or choose “Copy” from the Edit menu. Open the Preview application. Press Command-N or select “New from clipboard” from the File menu. You now have the screenshot in Preview.
In Preview, press Command-S or choose “Save…” from the File menu. You’ll get a dialog to save the file, with a choice of formats: JPEG, JPEG2000, OpenEXR, PDF, PNG, or TIFF. Pick whichever one you like. If you’re going to put the image into a Web page, PNG is usually the best choice. Preview will remember your choice for next time. Then save the file.
If you prefer, you can do the equivalent in Photoshop, Gimp, or any other image-processing application, but Preview has the advantage of launching quickly and keeping the process simple.
That’s it. You can now use Grab to save screenshots to a Web-friendly format.
Mad File Format Science 
How broadcast FM can wreck your receiving system
Today I came upon some news weird enough to justify a post on this long-dormant blog. Ars Technica reports that it “began on January 30 and afflicted Mazdas from model years 2014 to 2017 when the cars were tuned to the local NPR station, KUOW 94.9. At some point during the day’s broadcast, a signal from KUOW caused the Mazdas’ infotainment systems to crash—the screens died and the radios were stuck on 94.9 FM.”
That shouldn’t be possible, right? A broadcast FM signal is just frequency-modulated audio. It might deafen you or damage the speakers, but it shouldn’t make the receiver stop working! Well, actually, it isn’t just audio. Broadcasters can optionally use the Radio Broadcast Data System (RBDS), which supports encoded digital data. It uses a 57 kHz subcarrier, well above the limits of human hearing. The data is encoded at 1187.5 bits per second, a strange-sounding number that yields 48 cycles of the subcarrier for every bit. Error correction codes bring the effective data rate down to 730 bits per second.
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Posted in commentary, News
Tagged radio, software