Category: Ask Tim Grey

Today’s Question: I have started using smart previews [in Lightroom] so I can do most of my editing on a mobile device or on my laptop with the photos drive detached so it doesn’t spin all the time.

When I open Lightroom with the photos drive attached, will the XMP sidecar files that have new data from Lightroom Mobile editing or from editing with the smart previews get updated automatically or do I have to do something to ensure that they get updated?

Tim’s Quick Answer: If you have enabled the option to have Lightroom automatically update the XMP sidecar files, those updates will begin as soon as the source image files are available. The Lightroom catalog will be updated based on changes made via Lightroom Mobile (or Lightroom Web) as soon as Lightroom is connected to the Internet for synchronization.

More Detail: There are now a variety of ways you can work with your images in Lightroom, including the use of a feature-limited version of Lightroom on mobile devices and the ability to work with Smart Previews in Lightroom on a computer even when the source photos aren’t available.

In terms of working on mobile devices and with Smart Previews, the Lightroom catalog will be updated to reflect the changes you’ve applied as soon as synchronization is possible. That basically means that as soon as all of the devices in question have been connected to the Internet, updates will be synchronized. So, for example, when you apply an adjustment to an image with the mobile version of Lightroom, once your mobile device and your computer have been connected to the Internet Lightroom will be able to synchronize the data.

If you want the XMP files for RAW captures (or the actual image files for other captures) to be updated in addition to the Lightroom catalog, you can enable automatic updates. To enable automatic updates, go to the Metadata tab in the Catalog Settings dialog, which can be found on the Edit menu on Windows or the Lightroom menu on Macintosh. Then turn on the “Automatically write changes into XMP” checkbox, and Lightroom will update the source images with metadata updates based on changes you apply in the Lightroom catalog.

It is important to note that not all changes you apply in Lightroom can be written out to the XMP sidecar files (or source images). In general, features that are specific to Lightroom (such as pick and reject flags, collections, virtual copies, and more) cannot be saved in this way, and will only exist within the catalog.

Today’s Question: This may be very basic, but I’ve never understood why I need to see a flashing light on my camera indicating that photos are being written to the card. What benefit does that knowledge provide?

Tim’s Quick Answer: The light you’re referring to indicates that data is being written to the media card in the camera, which serves as a reminder not to eject the card or otherwise interrupt the process of writing data. Interrupting that process can cause files (photos and videos) to be corrupted or lost.

More Detail: When you capture a photo or video on a digital camera, the resulting file does not appear instantly on the media card in the camera. While the file can generally be written to the card very quickly, sometimes a little extra time is involved.

For example, when you capture a burst of photos, the image data is first stored in a memory buffer in the camera, and then written out to the media card. If you have captured a large burst of photos it can take considerable time to write all of the files to the media card, especially if the media card you’re using isn’t particularly fast.

During the time that data is being written to a media card, it is very important not to interrupt that process. If, for example, you capture a burst of ten photos and then immediately remove the media card from the camera, you would likely find that most of the image files never made it to the media card, and those that did may very well be corrupted.

So, the flashing light on your camera that indicates data is being written to the card is really a warning not to interrupt that process.

Many (if not most) digital cameras today will continue writing data to the media card even if you turn off the camera. You may have noticed, for example, that even after turning off the camera the flashing light continues to flash. However, if you remove the media card from the camera (or in most cases even open the battery door or the media card access door) you will interrupt the process of writing data to the card, and data may become corrupted or lost.

Today’s Question: When shooting for panoramas, is there a maximum number of individual photos to include? I got this message: “Unable to merge photos, not enough matching photos for merging”. I had 25 individual photos to merge. Was this too many?

Tim’s Quick Answer: There isn’t really a limit to how many photos can be merged into a composite panorama, other than limitations related to maximum pixel dimensions, file size, and memory available when assembling that panorama. In this case the issue you’re running into is likely that the content of the photos is not distinct enough for the software to accurately combine the photos.

More Detail: When capturing the individual frames for a composite panorama, each frame must be overlapped to some degree (generally around 20% to 50% depending on the lens focal length and other circumstances). That overlap enables software to look for similar features from one frame to the next, so the images can be blended together into the final panorama.

With a typical landscape panorama the software is generally able to find matching features among the overlapping areas of each pair of photos, enabling the composite image to be assembled with relative ease. However, if there are not distinct features across the full scene you’ve photographed, it can be difficult (or impossible) for the software to merge the images.

For example, I recently captured a composite panorama that included a boat at the far left end of the scene, with nothing but water across the rest of the scene. While there was certainly a considerable amount of texture in the water and sky that represented most of the scene I was photographing, there weren’t enough distinct features that could be aligned, since the waves would have changed from one frame to the next. As a result, I couldn’t find any software that could assemble that particular panorama.

It is still possible to assemble such a panorama with a manual approach, such as by using layers and masks in Photoshop. That can still be a challenge, of course, but when you are exercising direct control over the layer masks that are being used to blend the images together, you can find ways to blend them that will work for the final result.

As noted above, assembling a composite panorama that consists of a large number of photos generally won’t be a problem. Many applications are limited in terms of the total pixel dimensions that can be used for any image, and overall file size will be limited depending on the specific hardware and software configuration. But other than these types of limitations, you can assemble composite panoramas with a large number of individual frames, including individual frames that represent multiple rows of captures for the same scene.

Today’s Question: What would you suggest for an off-site copy of “All Photographs” in Lightroom, which would fit in a safe deposit box?

Tim’s Quick Answer: To create this type of “everything” backup for photos and your Lightroom catalog, I recommend using the “Export as Catalog” command to export all photos and a catalog that contains all of the information for those photos based on the information in your existing catalog. You can export that backup copy to an external hard drive, which can be placed in a safe deposit box (or other offsite storage).

More Detail: The “Export as Catalog” command in Lightroom enables you to export a Lightroom catalog based on the photos you’ve selected for export, along with copies of all photos being managed by that catalog. The only caveat is that you need to make sure that the actual image files are copied as part of this process.

You can export every single photo and video included in your Lightroom catalog by first selecting all photos within your catalog. To do so, go to the “All Photographs” collection in the Catalog section of the left panel in the Library module, and then choose Edit > Select All from the menu to select all images in your catalog.

Next, choose File > Export as Catalog from the menu. In the Export as Catalog dialog you can navigate to the location you want to use for saving the copy of your catalog and photos, such as an external hard drive specifically intended for this purpose. If needed you can also create a folder in that storage location to encapsulate all of the files and folders that will be created as part of this process.

In addition, it is very important to turn on the “Export negative files” checkbox. This checkbox is what actually enables the source image files to be copied, in addition to the catalog file that will be created as part of this process.

There are also options to build or include Smart Previews for your photos, and to include any other available previews that have already been generated for your photos. These items aren’t critical from a backup standpoint, since you could later re-generate all of those previews if needed.

When you click the Export Catalog button, a new catalog will be created based on the selected photos (all images in your catalog in this example), and all photos and videos will be copied as well, with the same folder structure you are already using for your existing catalog of photos.

Should you ever need to recover from that backup, obviously the photos you copied would be there, but you could also open the catalog that was created as part of this process within Lightroom in order to access all of the information you had added to the catalog for those photos up to the time of using the “Export as Catalog” command. Naturally you could essentially repeat this process periodically to “refresh” the backup you’ve created for offsite storage.

Today’s Question: This may be silly, but can you tell me how you calculated the number of color values available based on bit depth?

Tim’s Quick Answer: There are two “basic” steps to calculating the number of colors available based on bit depth. First you raise the number 2 to a power based on the bit depth you’re calculating, such as raising 2 to the 8th power for 8 bits per channel. Then you take the result from step one and multiply it by itself based on the number of color channels. In other words, you would cube the result for a three-channel RGB image to obtain the number of colors available for an 8-bit per channel RGB image.

More Detail: Bit depth refers to the number of bits used to store a specific numeric value, which in this case refers to pixel values in a digital image. Each bit can have one of two values, which represent “on” or “off” and are often described as “1” and “0” in the parlance of computer systems.

When we say that a value is “8 bits” we are essentially saying that the value can be represented by an 8-digit number, but where each digit can only be “1” or “0”. So the first digit can have one of two values, and the second digit can have one of two values, and so on. Thus, we can calculate the total number of possible values for an 8-bit number by multiplying 2 by itself a total of 8 times. For different bit depths, simply repeat the multiplication based on the bit depth value (in place of 8 used in the example here).

Of course, instead of multiplying 2 by itself multiple times, you can also simply raise the number 2 to a power based on the bit depth. So, for an 8-bit number you could raise 2 to the power of 8. This function is available on many calculators as an “x-to-the-y” function, which calls for entering “2”, then pressing the “x-to-the-y” button, followed by the power you want to raise 2 to.

At this point you will have the number of possible tonal values for a single channel. For an 8-bit value that would be 256 shades of gray for a black and white image. But for a typical RGB color image there are three channels (red, green, and blue). Therefore, you need to take the result you got from the first step and multiply it by itself based on the number of channels. So in this example you could multiply 256 by 256 by 256 (for a total of three instances of 256, if you will). That also translates into cubing the value.

So, completing our example here, 256 raised to the power of 3 produces a result of 16,777,216 possible color values for an 8-bit per channel RGB image. Keep in mind, of course, that this is only the theoretical maximum number of colors available, and the actual number represented in a given photo could be significantly lower.

Today’s Question: When shooting multiple vertical and horizontal photos for detailed panoramas, is it better to tilt the camera for the rows, or to raise/lower the tripod head?

Tim’s Quick Answer: For a typical composite panorama where you are photographing from a reasonable distance, either approach would be fine (though tilting would generally be easier). For closeup work, physically moving the camera would be preferred over tilting (or even panning) the camera.

More Detail: The key issue here is parallax and other distortion issues, which can create significant challenges when assembling the multiple captures into a composite panoramic image.

In general I recommend capturing the frames for composite panoramas at a lens focal length of 100mm or greater if at all possible. The reason is primarily to minimize distortion and parallax issues in the captures, in order to help ensure the individual frames go together into the final composite as smoothly and accurately as possible.

When capturing images at a focal length of around 100mm or greater, distortion will be minimized provided there are not any key subjects particularly close to the lens. If there are elements of the scene that are close to the lens, most of the parallax issues can be minimized by ensuring that the camera is rotating around the nodal point of the lens.

When you will be photographing a scene relatively close to the lens, it is best to actually move the camera across the scene for each capture, and move the camera up and down as needed for each row of the capture. This will help to minimize distortion overall, but it is also important to be sure that you are overlapping more than you otherwise would for this type of scenario.

When capturing a “typical” composite panorama, it is generally adequate to overlap each frame by about 20%. When distortion is a concern due to parallax issues, a shorter than optimal lens focal length, a close distance to the subject, or other related issues, it is a good idea to increase that overlap to about 50% of the frame for each capture.

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.