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En fotografía llamamos rango
dinámico a la amplitud de valores posibles o existentes en
una escala, normalmente la escala de luminosidad. Suele decirse
indistintamente que el rango es la "razón" o la "diferencia" entre
el valor más alto y el más bajo, aunque es fácil saber cuál de los
dos términos es el correcto en cada caso.
ADJUSTING LEVELS TO IMPROVE CONTRAST
Prerequisites: Understanding
histograms will make it easy to use the levels tool.
Levels is a simple tool available in most photo-editing software for improving contrast of the image. Using levels can increase the contrast to make the image look rich with saturated colors. In Photoshop, levels tool can be invoked by Image >> Adjustments >> Levels.
The levels tool shows the histogram with three sliders at the bottom of it, as you can see below.
Above is the levels display for the image shown below.
ADJUSTING BLACK POINT
The black slider to the left of the histogram(marked '1') determines the black point of the image, where all RGB values are zero. By shifting the black point to the right, all pixels to the left of the slider will be made completely black(RGB values zero). The histogram will be re-adjusted to reflect the new black value, resulting in reduction of overall brightness of the image. Note that this is not same as reducing the brightness using Brightness/Contrast tool. While Brightness /Contrast tool uniformly reduces the brightness of the image, black point slider of the levels tool affects darker portion of the image more than brighter portions. It also does not result in any shift in the white point. That is, all pixels that are completely bright(RGB values 255) remain unaffected. You can see the effect of moving the black point slider on the image below.
See that the image turns darker. Also see the input levels on the top, which indicates that the pixels with brightness 19 and below will become zero.
ADJUSTING WHITE POINT
The white slider to the bottom right of the histogram(marked '3') adjusts the white point of the image. Moving the white slider to the left results in all pixels to the right of the slider to become full white(RGB levels 255). Similar to moving the black slider, histogram will be re-adjusted to reflect the new position as white value(255), resulting in the overall brightness of the image. Again, this adjustment affects brighter parts of the image more than darker parts, and leaves the black point unaffected. See the effect of adjusting the white point below.
ADJUSTING MID-TONES
The middle slider(marked ‘2’) is used for adjusting mid tones(brightness level 128). For example, if you move the slider to the right, mid tones get shifted to the new position to the right, rendering the pixels to the left of the slider to go below the mid-tone value and hence reducing the brightness of the mid-tones. Moving the slider to the left results in pixels to the right of the slider go above mid-tone value, resulting in increase in brightness of the midtone. This results in change in the brightness of the mid tones without affecting black point and white point.
Here, I have moved the midtone slider to the right, resulting in reduction in midtone brightness. The ratio of new mid-tone value to the old-value is often called as 'gamma'. The middle text box above shows the value of gamma as you move the slider. In this case, it indicates that the new mid-tone has a brightness level that is 0.83 times the initial brightness.
INCREASE IN CONTRAST
Note that the changes made in the levels has improved the contrast of the image. See the comparison of the image before and after applying levels.
When adjusting levels, it is recommended to shift the black slider to the right to a point until the graph starts rising, and white slider to the left to a point until the graph starts rising. This gives the best contract without loosing any color information. After doing this, adjust the gamma to either side until the image looks at its best. This is exactly what I have tried to do above.
PREVENT CLIPPING OF COLORS
To ensure that no color information is lost because of clipping when moving black or white sliders, hold the Alt key when moving the sliders. On holding Alt key, the entire image look white. And as you move the slider, any clipped colors will start appearing on the screen. To ensure that no color information is lost, stop the slider at a point before you start seeing any colors on the screen.
ADJUSTING INDIVIDUAL COLORS AND BRIGHTNESS
The above adjustments were made on the overall image brightness. Level adjustments can also be made on single color channel by choosing the drop-down box on the top. However, adjusting levels of individual colors is a job for experts and is best not done, as it may result in color shift in the image.
The levels tool can also be used to for color correction of the image by using the eye-dropper tools seen in the bottom right of the tool. But this deserves a special attention, and can be a separate chapter by itself.
Levels is a simple tool available in most photo-editing software for improving contrast of the image. Using levels can increase the contrast to make the image look rich with saturated colors. In Photoshop, levels tool can be invoked by Image >> Adjustments >> Levels.
The levels tool shows the histogram with three sliders at the bottom of it, as you can see below.
Above is the levels display for the image shown below.
ADJUSTING BLACK POINT
The black slider to the left of the histogram(marked '1') determines the black point of the image, where all RGB values are zero. By shifting the black point to the right, all pixels to the left of the slider will be made completely black(RGB values zero). The histogram will be re-adjusted to reflect the new black value, resulting in reduction of overall brightness of the image. Note that this is not same as reducing the brightness using Brightness/Contrast tool. While Brightness /Contrast tool uniformly reduces the brightness of the image, black point slider of the levels tool affects darker portion of the image more than brighter portions. It also does not result in any shift in the white point. That is, all pixels that are completely bright(RGB values 255) remain unaffected. You can see the effect of moving the black point slider on the image below.
See that the image turns darker. Also see the input levels on the top, which indicates that the pixels with brightness 19 and below will become zero.
ADJUSTING WHITE POINT
The white slider to the bottom right of the histogram(marked '3') adjusts the white point of the image. Moving the white slider to the left results in all pixels to the right of the slider to become full white(RGB levels 255). Similar to moving the black slider, histogram will be re-adjusted to reflect the new position as white value(255), resulting in the overall brightness of the image. Again, this adjustment affects brighter parts of the image more than darker parts, and leaves the black point unaffected. See the effect of adjusting the white point below.
ADJUSTING MID-TONES
The middle slider(marked ‘2’) is used for adjusting mid tones(brightness level 128). For example, if you move the slider to the right, mid tones get shifted to the new position to the right, rendering the pixels to the left of the slider to go below the mid-tone value and hence reducing the brightness of the mid-tones. Moving the slider to the left results in pixels to the right of the slider go above mid-tone value, resulting in increase in brightness of the midtone. This results in change in the brightness of the mid tones without affecting black point and white point.
Here, I have moved the midtone slider to the right, resulting in reduction in midtone brightness. The ratio of new mid-tone value to the old-value is often called as 'gamma'. The middle text box above shows the value of gamma as you move the slider. In this case, it indicates that the new mid-tone has a brightness level that is 0.83 times the initial brightness.
INCREASE IN CONTRAST
Note that the changes made in the levels has improved the contrast of the image. See the comparison of the image before and after applying levels.
When adjusting levels, it is recommended to shift the black slider to the right to a point until the graph starts rising, and white slider to the left to a point until the graph starts rising. This gives the best contract without loosing any color information. After doing this, adjust the gamma to either side until the image looks at its best. This is exactly what I have tried to do above.
PREVENT CLIPPING OF COLORS
To ensure that no color information is lost because of clipping when moving black or white sliders, hold the Alt key when moving the sliders. On holding Alt key, the entire image look white. And as you move the slider, any clipped colors will start appearing on the screen. To ensure that no color information is lost, stop the slider at a point before you start seeing any colors on the screen.
ADJUSTING INDIVIDUAL COLORS AND BRIGHTNESS
The above adjustments were made on the overall image brightness. Level adjustments can also be made on single color channel by choosing the drop-down box on the top. However, adjusting levels of individual colors is a job for experts and is best not done, as it may result in color shift in the image.
The levels tool can also be used to for color correction of the image by using the eye-dropper tools seen in the bottom right of the tool. But this deserves a special attention, and can be a separate chapter by itself.
Dumping your entire music collection onto an iPod is a simple, one-click process.
But what about getting your music off an iPod? You'll find that's not so easy. Apple's iTunes software only lets you put the music onto the player, and not the other way around. The iPod/iTunes combo was designed with this restriction built in to prevent piracy and illicit trading. However, there are a number of legitimate reasons you might need to transfer songs from your iPod to your hard drive. For instance, if that fateful day arrives and your PC hard drive crashes, you can restore your music collection without re-ripping dozens of CDs.
Fortunately, there are many applications you can use to get your tunes off your iPod. Some of them are even free, so they won't cost you a thing.
What You'll Need
1. An iPod (obviously)
2. Either a Windows or Mac machine.
The simplest method for grabbing tunes off of your iPod is also the geekiest. Just enable the "Disk Mode" feature of the iPod from within iTunes, which will allow you to mount the iPod as a hard drive. Then, you can browse the disk using Windows Explorer or the Mac's Finder.
How To (Mac)
On a Mac, you'll need to enable hidden folders in the Finder.
1. Launch the Terminal by going to Applications > Utilities and double-clicking on Terminal.app.
2. Paste in these lines of code:
3. If you ever want to make the hidden folders disappear again, just run the code again, but change TRUE to FALSE.
How To (Windows)
Similarly, you can copy songs from an iPod onto a Windows PC by enabling hidden folders to be viewed. Here's how.
1. Open your My Computer directory.
2. Double click on your iPod.
3. Go to Tools > Folder Options > View.
4. In the Advanced Settings list, under Hidden files and folders, check the radio button for Show hidden files and folders. Then click OK.
5. Go to iPod_Control > Music. You'll see the iPod's music organized randomly into a bunch of folders. Copy those into your music directory.
Although the filenames of the songs will be scrambled, their ID3 tags will be intact, so you'll be able to navigate the songs as usual on your computer or another iPod.
While these slightly inconvenient methods work, there are plenty of software apps that make the process of browsing and copying files much easier.
Third Party Apps
Senuti
Senuti is a free, open-source, Mac-only application that allows you to recover songs, photos and movies from your iPod. Senuti features drag-and-drop transfer of songs and playlists. Senuti also allows you to copy songs from a Windows formatted iPod onto a Mac.
The main downside to Senuti is that it doesn't recognize duplicate tracks. If you have a playlist with 10 songs on your iPod and the same playlist already exists in iTunes, Senuti will add the same 10 songs again. You can stop Senuti from duplicating the actual song files by choosing "overwrite songs" in the preferences, but there doesn't seem to be a way to stop the duplication of songs within playlists.
iPodRip
IPodRip works in both Mac OS X and Windows. It has drag-and-drop support for moving songs from your iPod directly into iTunes, as well as one-click importing to restore a local collection. IPodRip also features a number of nice extras not found elsewhere, such as a database integrity check for your iPod database, an option to export your library information to HTML or XML formats, and the ability to sync metadata between your iPod and iTunes.
IPodRip is shareware, and it costs $15. The unlicensed version will expire after 10 uses. So, if you just need to recover from a hard drive failure or similar one-time problem, iPodRip can do it for free.
iPod Access
This is another cross-platform offering. Copying songs with iPod Access is simple: Just highlight the songs you want to copy and click "Add to iTunes." The trial version only allows you to transfer five songs at a time. A full license costs $20. When it comes to handling song transfers, iPod Access gives you more options than some of the other programs in the list, including the option to rename the songs in a variety of formats. IPod Access will also only overwrite existing files on your computer if the iPod copy is newer.
Anapod Explorer
This Windows-only app raises the bar somewhat compared to the other programs. It doesn't just recover files, it also has a whole bunch of additional features like ID3 tag editing and other file management tasks. The downside is that those additional features come at an additional cost -- the full version of Anapod Explorer is $30.
Anapod Explorer includes a separate program, Anapod Xtreamer, which allows you to browse your iPod in a web browser. Xtreamer makes it easy to transfer files, not just from your iPod to the connected computer, but to any computer on your network.
Podworks
Another Mac-only program, Podworks boasts a number of ways to recover your music from an iPod. Podworks can send the songs straight into iTunes by using the "Send All to iTunes" option, or it can transfer songs to any other location on your hard drive. Podworks lacks the desirable-drag and-drop features of other applications, but it does avoid duplicating songs. The shareware app costs $8. There is also a 30-day trail version which is limited to 250 song transfers.
XPlay
With XPlay there is no bulky interface, no fluff, nothing to get in the way of you and your music. XPlay's powerful drag-and-drop ability makes transferring music on and off the iPod quick and simple. To copy music off the iPod, simply double click the iPod icon and navigate to the songs folder. Once there you see a listing of all your songs. You can drag-and-drop your music to and from the songs folder. It is that easy.
YamiPod
This is the only tool of the bunch that supports all three major operating systems -- Windows, Mac OS X and Linux. It's also free. YamiPod can transfer songs to and from an iPod, and it offers a good range of options for handling duplicates. YamiPod also has some extra features not found in the other programs, including the ability to create playlists and send them to Last.fm. YamiPod can add song lyrics to your tunes, and it also supports Mac OS X's Growl notification system.