Ask Tim Grey

Today’s Question: As a follow-up to your answer about compression for RAW captures, can you address the impact of the bit depth option for cameras the offer several different bit depth settings for RAW captures?

Tim’s Quick Answer: The bit depth of your photos primarily relates to the total range of tonal and color values available. Therefore, a lower bit depth can reduce color fidelity and dynamic range, and increase the risk of posterization in your photos.

More Detail: When information in an analog form (such as light) is converted to a digital value (such as the numeric color values for a single pixel), bit depth plays a role. Put simply, bit depth determines how many individual values are available. In the context of a digital photo, bit depth determines the total number of tonal and color values available.

For example, an 8-bit per channel color image can make use of almost 16.8 million individual color values. A 16-bit per channel color image can theoretically make use of more than 281 trillion individual color values.

When you have more color values available, the differences between neighboring color values are very small, and so gradations in an image can be incredibly smooth. When you have a relatively small number of color values available, the difference between neighboring color values is relatively large, and so it can be difficult (or impossible) to retain smooth gradations in an image.

Many (perhaps most) digital cameras today use 14-bit per channel analog to digital conversion for RAW captures. Some higher-end cameras use 16-bit per channel, and some older or lower-end cameras employ 12-bit per channel conversion. JPEG captures, by the way, always represent 8-bit per channel conversion.

If your camera is capable of 14-bit conversion, it might also offer a 12-bit option for RAW captures. The result would be a smaller file size, but also a smaller number of possible tonal and color values in the image. Specifically, an image with a 14-bit conversion could employ up to about 4.4 trillion possible color values, while a 12-bit conversion would translate to a maximum of about 68.7 billion possible color values.

Whether or not the “extra” potential color values available at a higher bit depth are going to be of much help depends in large part on the amount of processing you’ll apply to the photo. If you apply many strong adjustments to a photo, you’re going to lose a certain amount of detail, and a higher bit depth will be helpful. If a photo requires only modest adjustments, a lower bit depth will work out perfectly fine.

Naturally it is difficult to quantify the precise potential benefit for a given photo. Some photos will benefit more from a higher bit depth than others, and your workflow plays a significant role here. That said, my personal preference is to opt for the higher bit depth, even though that translates into larger file sizes. I may be getting a benefit I don’t really fully leverage, but I still prefer the peace of mind of having as much information as possible in my image files.

Today’s Question: My camera gives the option of taking pictures in Compressed RAW or Uncompressed RAW.  Since compressed RAW is a smaller file size I see its advantages, but does the compressed file photo lose any capabilities when post processing in Lightroom or Photoshop?

Tim’s Quick Answer: The answer here depends on your specific camera. Some cameras offer lossless compression when they provide a Compressed RAW format, while others use lossy compression. If the RAW capture employs lossy compression, there is a certain degree of risk that some detail or quality will be lost.

More Detail: As most photographers are probably aware, a RAW capture represents (with a few limited exceptions) the capture data exactly as that data (the light) was recorded by the image sensor in your camera.

Other capture formats, such as JPEG or TIFF, involve in-camera processing to take the RAW capture data and convert the information into actual pixel values. One of the advantages of a RAW capture is that you can exercise some additional control during the process of converting the RAW capture to a pixel-based format in post-processing.

Many cameras now offer a compression option for RAW captures, primarily focused on reducing the file size for those captures. This helps to reduce storage usage on the media cards you use when capturing photos, and also reduces the amount of time those RAW captures require to download to your computer or otherwise copy to a different location.

There are a variety of ways compression can be applied to an image file. You can think of lossless compression as simply recording information in a more efficient way. For example, imagine you had a photo with a row of 1,000 pixels that were all the same shade of blue. It would be far more efficient to say “1,000 blue pixels” than to repeatedly say “blue pixel” one thousand times.

Lossy compression does cause some information to be lost. Let’s assume that we modify the example above to involve a row of 1,000 pixels where each pixel is a slightly different shade of blue. With lossy compression you might still say “1,000 blue pixels”, even though each pixel is a slightly different shade of blue. We haven’t lost a huge amount of information, but some information was lost.

With lossy compression for a RAW capture you may lose a slight amount of color fidelity, dynamic range, and smoothness of gradations. In most cases the loss would be so subtle as to be nearly impossible to see without exaggerating the differences using software.

If your camera offers a lossless compression option for RAW captures, I would certainly be in favor of using that option. If the only compression option for your RAW captures is lossy compression, I would acknowledge that the risk to your photos is minimal. However, I personally prefer not to use lossy compression for RAW captures, mostly from a philosophical standpoint. After all, one of the key reasons to use RAW capture in the first place is to preserve as much information as possible in your captures.

Today’s Question: Regarding image posterization in the Library module that does not appear in the Development module [in Lightroom], isn’t it possible the image may not have enough resolution to display at the magnification the user has set in the Library Module?

Tim’s Quick Answer: It is true that the preview image available in Lightroom may not have adequate resolution to present a good quality preview, especially when you zoom in on the photo. However, that would present a different visual effect than the posterization that can occur with the preview images in the Library module in Lightroom.

More Detail: The previews for your photos presented in Lightroom are created differently for the Library module versus the Develop module. In the Library module you are essentially viewing a JPEG preview for each image, while in the Develop module you are viewing a full-resolution preview based on the underlying image file and the adjustments you’ve applied in the Develop module. This is why, for example, when the source image files are not available (such as when you’ve disconnected an external hard drive) you can still view your photos in the Library module but not in the Develop module.

Because the Develop module is creating a real-time preview based on the underlying image file and the adjustments you’ve applied, the source image must be available to view the image in the Develop module. That also means you’ll see the most accurate (and highest quality) view of your image by viewing it in the Develop module.

In the Library module you are viewing a JPEG preview of your photo. In general that means the overall quality may not be as high as what you see in the Develop module. Among other things, that can cause a degree of posterization (loss of smooth gradations of tone and color) as noted in a previous edition of the Ask Tim Grey eNewsletter.

If the resolution is low (such as when zooming in on an image for which a 1:1 preview has not been generated yet) the quality will suffer, but not in a way that produces posterization. Instead, the image will take on something of a “jagged” appearance. For example, curved lines within the image will look rough rather than smooth, with more of a “stair-step” pattern than a smooth curve.

Both of these issues can obviously impact your perception of the overall image, especially when taking a close look as specific details in a photo. Therefore, it is always best to use the Develop module in Lightroom when you want to critically evaluate the quality and details of a photo.

Today’s Question: My camera (Olympus OMD EM1) has settings for both 1/2 and 1/3 F-Stops. It also has settings for full (1 stop) and 1/3 ISO. What is the best combination of settings to use?

Tim’s Quick Answer: The decisions here primarily relate to a choice between more precise control over exposure versus a more streamlined workflow for adjusting exposure settings. Although I’m a self-confessed control freak, I prefer to use half-stop increments for exposure settings and full-stop increments for ISO.

More Detail: Let’s first consider the overall exposure settings, meaning the increments for setting the lens aperture (f-stop) and shutter speed. With most cameras you can choose between one-half stop increments and one-third stop increments.

Opting for one-third stop increments obviously provides you with greater precision in setting your exposure. I would argue that for most photographic situations, that precision doesn’t provide a significant advantage. After all, the incremental benefit in being able to shift exposure in one-third stop increments is only about one-sixth of a stop.

In other words, in the worst case scenario your exposure would be off by about one-sixth of a stop if you used one-half stop increments instead of one-third stop increments. For many (if not most) typical photographic scenarios, an exposure “error” of one-sixth of a stop won’t create any insurmountable problems for the photo.

That said, there are certainly situations where greater precision can be helpful. For example, with a scene that contains extreme contrast, having the ability to adjust exposure in one-third stop increments could help maximize the amount of detail in the extreme highlights or shadows, by virtue of being able to set the exposure with greater precision.

When it comes to the ISO setting, I think it is worth keeping in mind that the primary impact of the ISO setting is noise. Raising the ISO enables you to achieve a faster shutter speed, for example, but at the cost of additional noise in the final image.

Having the ability to adjust ISO in half-stop increments helps ensure you can adjust the overall exposure settings while minimizing the increased noise in your captures. I personally prefer the efficiency of being able to adjust exposure more quickly when it is necessary by adjusting the ISO setting in full-stop increments.

To be sure, raising the ISO setting by a half-stop more than is really necessary for a particular scenario will generally result in more noise in the photo than you could have otherwise expected. I tend to be somewhat conservative with increases in the ISO setting in any event, so to me this isn’t a serious concern. In addition, most newer cameras provide rather good performance when raising the ISO setting to moderately high values.

So, I prefer to use one-half stop increments for my exposure settings, and full-stop increments for my ISO setting. But there are certainly many photographers who prefer greater precision for these adjustments, and I certainly appreciate that perspective. In other words, this largely comes down to a personal decision for each photographer, choosing a balance between precision and the potential speed of exposure setting adjustments.

Today’s Question: I just noticed there is now a “Content-Aware” checkbox for the Crop tool in Photoshop. When would this apply, and do you recommend using it?

Tim’s Quick Answer: The Content-Aware feature for the Crop tool is used when you set the crop box outside of the boundary of your photo. My general recommendation is to only use this option for situations where the area being added to the image is relatively simple, such as when extending the sky a little.

More Detail: When we talk about cropping a photo, generally we’re talking about removing part of the image. However, it is also possible in Photoshop to extend the crop box beyond the boundary of a photo, adding additional space in the image. This is especially likely, I find, when you are rotating the image along with cropping, such as to correct a horizon that isn’t straight. In order to get the crop you want, you may end up with a triangle of space where one corner of the crop box extends outside the image area.

Under normal circumstances without the Content-Aware feature, the extra space added by a crop box that extends beyond the boundary of the image would be filled with the current background color defined on the color picker at the bottom of the toolbox.

If you turn on the “Content-Aware” checkbox on the options bar for the Crop tool, and the crop box extends beyond the boundary of the image, then when you crop the image the empty space will be filled using the Content-Aware technology.

So, for example, if you are rotating the image to straighten the horizon, you might find that a crop that remains within the image area will cut off part of a cloud formation you particularly like. If you extend the crop box to include the full cloud formation, the crop box would extend outside the image and you’d end up with (by default) a white triangle in that area of the photo.

With the “Content-Aware” checkbox turned on, that empty space would instead be filled through the use of the Content-Aware technology. If the surrounding area of the photo is relatively simple, this will generally produce very good results. If the area is a bit complex, with textures and shapes that will make any duplication obvious, this feature can be problematic.

So, for simple situations I recommend using the Content-Aware feature for the crop tool. For more challenging circumstances I recommend leaving this option turned off, and then using a combination of the Content-Aware Fill command along with the various image cleanup tools to fill in the empty area in a way that will not be problematic in the final image.

Today’s Question: Some of my photos in Lightroom show up with the color labels I have assigned to them, but others show up with a white color label. What does a white color label mean, since I don’t see any way that I can assign a white color label myself?

Tim’s Quick Answer: A white color label in Lightroom indicates that a color label has been assigned to a photo, but the definition for that label doesn’t match any of the colors available. This situation is caused by different software using different terms for the individual colors available for the color label feature. You can’t actually assign a white color label, other than by intentionally creating a mismatch among color label definitions.

More Detail: When you add a color label to a photo, you aren’t really assigning a color to the image. Instead, you’re adding a word to the Label field in metadata.

Since the color label feature is implemented with the assignment (and display) of a color to a photo, it makes sense that the Label field would be populated by the name of the color assigned to a photo. So, for example, when you assign a color label to a photo in Lightroom, the Label field will be populated with the word Red, Yellow, Green, Blue, or Purple.

Other software might use different words for the Label field when you assign a color label. One of the more notable examples is Adobe Bridge. Instead of using words that define the actual colors, when you assign a color label in Adobe Bridge you are adding the word Select, Second, Approved, Review, or To Do.

If you see a white color label when you expected to see a red color label, it could mean that the word Select was assigned via a red color label assignment in Adobe Bridge. Since by default Lightroom is looking for the word “Red” rather than “Select” to define a red color label, when it finds the word “Select” (or any other word that hasn’t been defined in Lightroom as a color label) then a white color label is displayed instead.

If you have this sort of mismatch among some of your metadata, you can certainly update your metadata based on your newer workflow. If you had only been using Adobe Bridge, for example, and then started using Lightroom, you could change the definition of color label values in Lightroom to match those from Adobe Bridge. You can find those settings by choosing Metadata > Color Label Set > Edit from the menu.

You could also update your “outdated” color label assignments from Adobe Bridge in Lightroom. For example, you could use the Metadata tab of the Library Filter Bar (View > Show Filter Bar from the menu) to view all of the current names being used for color labels, and filter for individual names. Using the example above, you could filter for color labels that were assigned the word “Select”, then select all of those images and assign a red color label to update the word used in the Label field for those images, and thus update the display of the images to a red label rather than a white label.

To learn more about cleaning up metadata and other “messy stuff” in your Lightroom catalog, check out my “Cleaning Up Your Mess in Lightroom” video course bundle here:

http://timgrey.me/atgmess

Today’s Question: Why is it that a JPEG on my desktop says its 947KB and when I open it in Photoshop it says it is 14.4MB?

Tim’s Quick Answer: In this case Photoshop isn’t reporting the actual file size on your hard drive, but rather the total amount of data based on pixel information. In other words, Photoshop is not taking into account the compression that will be applied when you save an image as a JPEG file.

More Detail: The file sizes that can be displayed on the status bar below the image window in Photoshop don’t actually report file size, but instead report what is referred to as the document size. There are actually two document sizes displayed, which can provide you with an idea of what sort of file size to expect for an image, but only for certain circumstances.

If you display the Document Sizes option on the status bar below the image, the file size indication on the left represents a flattened version of the image, and the file size indication on the right represents a layered version of the image.

In other words, the first number can be thought of as the file size you could expect if you saved the image as a TIFF file with no compression applied, but with all layers flattened. The number on the right is the estimated file size if you save the file as a TIFF image without compression and with all layers intact.

When you save an image as a JPEG image, it will always be a flattened version of your document in Photoshop, because JPEG images can’t contain layers. In addition, JPEG images always have compression applied to them. That compression helps to reduce file size, though it also has a negative impact on overall image quality. That is why a JPEG is good for sharing in certain contexts, but not ideal as a “master” image file format.

In addition, you can adjust the “Quality” setting for a JPEG image, which impacts not only the overall image quality but also the file size. But again, the Document Sizes information display that is available for the status bar for your photos relates more to the amount of information contained in the image you’re working with, which doesn’t directly translate into the actual size of the file that will be saved on your hard drive.

Today’s Question: I just tried to load my Lightroom catalog and got a message it is corrupt. I tried all the suggestions Lightroom made to no avail. Any suggestions? I have a week-old backup, but will lose a fair amount of data if I have to utilize it.

Tim’s Quick Answer: I would first make some additional efforts to open the catalog, but failing that would want to either restore from a backup or re-import into a new catalog if you had enabled the option to automatically write metadata updates to XMP.

More Detail: Naturally the ideal solution here would be to regain access to the Lightroom catalog that has become corrupted. Unfortunately, if the catalog has become corrupted there isn’t much chance that you’ll be able to recover it. However, you might try quitting Lightroom and then confirming that none of the temporary files are included along with your Lightroom catalog. One simple way to test this out is to copy the corrupted “lrcat” file (the actual catalog file) to a different location, and then double-click to open that catalog file in Lightroom. If that fails, chances are you won’t be able to recover your catalog.

If you had previously enabled the “Automatically write changes into XMP” on the Metadata tab of the Catalog Settings dialog in Lightroom, you can recover most of the information from your corrupted catalog by simply creating a new catalog and importing all of your photos into that catalog, using the “Add” option at the top-center of the Import dialog.

It is very important to keep in mind that some information from your original catalog will be lost if you take the approach of creating a new catalog and importing all of your photos into that catalog. For example, pick and reject flags, membership in collections, the history in the Develop module, virtual copies, and some other details that relate to Lightroom-specific features are not written to your images when you enable the “XMP” option noted above. However, all standard metadata such as star ratings and keywords will be retained if you had previously enabled the “XMP” option in the Catalog Settings dialog.

The last option, as noted in the question, is to recover from the most recent catalog backup. Obviously this means you will lose any information that was added to the corrupted catalog since the time of your last backup. You may therefore need to update information for some of your photos, and even re-import photos that had been imported after your latest backup. But at least this approach will provide you with most of the information that would have otherwise been lost in the absence of a backup.

This type of situation does underscore some of the challenges associated with the use of a catalog in Lightroom. There are many advantages to having that catalog as well, but it is very important to protect yourself from the risk of corruption of your Lightroom catalog, through frequent backups and other workflow practices.

Today’s Question: You suggested backing up the catalog to the same external drive as the one used for photo storage. Currently my backup is stored on my MacBook Pro. Where do I make this change? I don’t see a setting for that in Preferences.

Tim’s Quick Answer: The location where you want to store the backup copy of your Lightroom catalog can actually be specified within the actual backup dialog that appears when it is time to create a new backup of your catalog.

More Detail: Within the Catalog Settings dialog you can specify the frequency for backing up your Lightroom catalog. The options include backing up daily, weekly, monthly, every time you exit Lightroom, or never. In addition, there is an option to backup the next time you exit Lightroom. However, within the Catalog Settings dialog (as well as the Preferences dialog) there is not an option to specify the location where you want to store the backup.

Instead you can specify the backup location within the Back Up Catalog dialog. The Backup Folder label identifies the current location for your catalog backup, which by default will be the same folder location as your actual catalog files. As noted in yesterday’s Ask Tim Grey eNewsletter, I recommend storing the backup in a location separate from the catalog.

Within the Back Up Catalog dialog you can click the Choose button to the right of the Backup Folder label where the existing path is indicated. You can then choose a new location for your backup, such as the external hard drive where you store your photos if that is the approach you use. Once you change the backup location, that will remain the location for the backup of the current catalog unless you change the location again in the future.

Today’s Question: My question is when I exit Lightroom and want to backup files where should I direct it to backup? I have an external hard drive and I back it up using GoodSync. I know my photos are on my external hard drive, but I am just wondering where to store my backup.

Tim’s Quick Answer: I recommend backing up your Lightroom catalog to an external hard drive. If you are using an external hard drive as the primary storage location for your photos, I recommend using a folder on that same drive as the location where your Lightroom catalog backups are stored.

More Detail: When it comes to making a backup of your Lightroom catalog, I feel it is important to ensure the backup is stored in a location that is different from the location where the source catalog is stored. After all, if you need to recover from a backup because the hard drive containing your Lightroom catalog failed, your only option will be to recover from a backup on a different storage device.

By default Lightroom will store the backup of your catalog in the same general location as the original catalog. I recommend changing that default location to a drive that is separate from the drive where your catalog is stored.

If you store your photos on an external hard drive, I think it makes perfect sense to backup your Lightroom catalog to a folder on the same external hard drive where you store your photos. This approach has the added advantage of ensuring that when you backup your photos you are also backing up your backup copies of the Lightroom catalog, providing additional redundancy.

Of course, if you store your Lightroom catalog on an external hard drive along with your photos, then I would recommend storing Lightroom’s backup of the catalog on a different hard drive, such as the internal hard drive on your computer. The key is to store backup copies separate from the source files being backed up.