Category: Ask Tim Grey

Today’s Question: How does JPEG compression affect the dynamic range available on the overall image and how the display used affects each characteristic of the final image?

Tim’s Quick Answer: JPEG compression doesn’t technically affect the dynamic range potential of the image, but does affect overall image fidelity and detail. The characteristics of the display being used have a potentially significant impact, though with modern displays this isn’t generally a major issue.

More Detail: In the context of photography, dynamic range is most applicable in the context of capturing an image in the first place. In other words, dynamic range mostly relates to the range the camera is able to capture from the darkest shadows to the brightest highlights.

Once the image data is captured, the dynamic range potential of the digital image is somewhat fixed based on how the image is processed and the bit depth. And even the bit depth is more applicable to the smoothness of gradations rather than a strict dynamic range at this point. After all, a digital image can always have a dynamic range that extends all the way from pure black to pure white. What’s more important is how pixel values were mapped to the digital image based on capture data.

One of the significant issues with saving an image as a JPEG is that the image will only support an 8-bit per channel bit depth. That translates to only 256 shades of gray for a black and white image, and almost 16.8 million colors for an RGB image. This compares to 65,536 shades of gray for a 16-bit black and white image, and over 281 trillion possible colors for a 16-bit RGB image.

The reduced bit depth reduces the potential for detail in the image and increases the risk that gradations of tone and color won’t be smooth. Furthermore, JPEG compression reduces detail and perceived sharpness in the image.

When it comes to the digital display of an image (whether JPEG or something else), the attributes of that display play a key role. Display resolution determines the perceived quality of the image. For example, a display with a 4K resolution will provide a crisper view even if set to a lower resolution. The dynamic range and color space capabilities of the display can also affect perceived image quality. For example, just because an image contains excellent shadow detail does not guarantee that the shadow detail will be visible on the monitor display, depending on the specifications and configuration of that display.

Today’s Question: Please explain the difference between “sensor dynamic range” and “image bit depth”. I hear lot of confusion about those two measures.

Tim’s Quick Answer: In some respects, these two factors describe the same (or at least similar) attribute, just based on a different context for each. They both relate to the total range of information (such as tonal range or color range) a photo could potentially contain.

More Detail: The dynamic range of the image sensor on a camera determines the maximum tonal range the camera is able to contain in a single capture. It relates to the difference between “empty” or “full” for each of the photodiodes that ultimately represent the pixels in the final image. Empty in this context means no electrical charge based on the amount of light detected, and full means the maximum charge.

Dynamic range is a measure of the difference between the darkest value (empty) and the brightest value (full) that the image sensor can capture. I think a reasonable (though abstract) analogy is to think of the image sensor as being comprised of buckets that are capturing light. An empty bucket is black, and a full bucket is the brightest value that can be recorded (theoretically white). Cameras with larger buckets can capture a greater dynamic range. For example, with relatively small buckets the sun might be blown out in a photo, while with relatively large buckets detail might be retained in the sun.

Ultimately, the dynamic range of the camera relates to the maximum range of tonal values you can capture with your camera, without blocking up the shadows or blowing out the highlights. In other words, the camera’s dynamic range determines the total potential for tonal range in the original captures for your photos.

The bit depth, while similar, plays a bit of a different role. The bit depth relates to the total number of tonal or color values that are possible for an image. For an image sensor, the bit depth of the processing from an analog signal (light) to discreet digital values can be performed at varying bit depths. In this context, the bit depth relates to how many different values can be recorded between black and white, for example, which in turn determines things like how smooth the gradations from dark to bright areas can be.

Once an image has been digitized, the bit depth determines the total number of tonal or color values that are possible. For example, an 8-bit per channel grayscale image can contain a maximum of 256 shades of gray, while a 16-bit per channel greyscale image can contain up to 65,536 shades of gray. For RGB color images the total number of possible colors is almost 16.8 million for 8-bit per channel images, and over 281 trillion for 16-bit per channel images.

In terms of image processing, for optimal quality you’ll want to ensure you’re working in the 16-bit per channel bit depth. For the camera, dynamic range is a product of the image sensor, so you’ll want to choose a camera based on maximum dynamic range if that is important to you. Furthermore, for optimal image quality with smooth gradations of tone and color, a higher bit-depth for the analog to digital (ADC) processing is preferred. Some cameras do offer 16-bit per channel in-camera processing, while many others only support 14-bit or even 12-bit processing.

Today’s Question: I know I should be routinely keywording my images when I upload them, but seldom do. With all the advances of AI, are there any apps or services that will do that automatically?

Tim’s Quick Answer: There are tools available that address the role of keywording based on AI from two different angle. So, in large part the first step is deciding which approach might make the most sense to you, and which software tools support that approach.

More Detail: There are software tools that can be used to assign keywords to photos based on image analysis driven by AI technology, which is the primary focus of today’s question. These tools enable you to have images analyzed, and then have keywords assigned to them automatically.

One option is ON1 Photo Keyword AI (https://bit.ly/on1keyword), which in my experience seems to be the more effective tool for adding keywords based on image analysis. It can be a bit slow to analyze images, but it is also relatively comprehensive in assigning keywords. Of course, depending on your preferences, you may find the automatic keywording to be a bit too comprehensive, with a wide variety of concepts and abstract terms included among the potential keywords that can be assigned to your photos. Another tool in this category, by the way, is Excire Search (https://excire.com/en/excire-search/).

However, an argument could be made that this type of software may become somewhat obsolete relatively soon. That’s because other software tools approach this same concept from something of the opposite direction.

With software such as Adobe Lightroom (the cloud-focused version, not Lightroom Classic), the Photoshop Elements Organizer, Apple Photos, and Google Photos (among others), you can actually search for images in your library based on AI image analysis. In other words, you can find photos based on their content without actually having to assign keywords.

There are advantages (and disadvantages) with both approaches. The advantage of AI-based keywording is that the keywords actually get assigned to your photos, so those keywords can be leveraged beyond the specific software you’re using. The advantage of image search powered by AI is that you can find photos without having to add keywords to metadata, and you also avoid the clutter of having numerous keywords assigned to images.

You could easily argue either side of this decision. However, my view is that while keywording can indeed be helpful in organizing and locating photos, as the AI search capabilities improve the notion of using keywords may seem somewhat old-fashioned.

For the moment, the key challenge in my mind is the workflow considerations. If you’re going to use AI-based tools for assigning keywords to your images, you’re going to introduce a bit more complexity to your workflow. If you’re going to depend on AI-based search, you need to accept that keywords won’t be added to metadata. Perhaps more significantly, if you want to use AI-based search you need to consider whether you’re willing to switch to a different software application for managing your photos to take advantage of these features that aren’t offered universally.

Today’s Question: As a follow-up to your answer about using AI Denoise, how do you decide when to use this rather than the manual noise reduction in Lightroom Classic?

Tim’s Quick Answer: Based on my experience, I consider using the Denoise feature when an image has extreme noise that isn’t responding well to manual noise reduction. I’ve also found that the Denoise feature in Topaz Photo AI (https://www.topazlabs.com/topaz-photo-ai/ref/273/) generally produces better results than Adobe’s current Denoise feature.

More Detail: Overall, I have had mixed results with the Denoise feature found in Adobe products such as Lightroom Classic and Camera Raw. In some cases it works remarkably well, but in others there is too much degradation of texture and sharpness in the image, even when used at a moderate setting.

As a result, I’ve gotten in the habit of using the manual noise reduction as a first step for noisy images, to see if I can get a good result without using Denoise.

For situations where I’m not happy with the results using manual noise reduction, I’ll try the Denoise feature. Sometimes it works great, and sometimes I’m left disappointed. But my point is that I’ve not found Adobe’s Denoise feature to be reliable enough that I use it as my primary tool for dealing with noisy images.

In the process of exploring other options, I also recently spent some time testing the updated Denoise feature in Photo AI from Topaz Labs. I was quite impressed with the results, and in most cases found that the Denoise feature from Topaz produced superior results to Denoise from Adobe.

This is obviously a moving target, as both companies will surely continue to improve the results we can achieve with their respective Denoise features. For the moment though, I’m finding that Topaz Photo AI is providing the best Denoise solution, and so it is my go-to tool for images that have significant problems with noise.

You can learn more about Topaz Photo AI here:

https://www.topazlabs.com/topaz-photo-ai/ref/273/

Today’s Question: When is the best time to apply AI Denoise in the Lightroom Classic workflow? Should it be done early or late in the process? Or does it matter?

Tim’s Quick Answer: Ultimately, the answer is that it doesn’t matter when you use Denoise in Lightroom Classic. However, when it is needed I prefer to apply Denoise early in my workflow, as it can have a significant impact on how I approach other adjustments for the image. I expect this will become even less of a consideration once Lightroom Classic is (presumably) updated to match the capabilities of Camera Raw.

More Detail: With the current version of Lightroom Classic, when you use the Denoise feature based on AI technology (rather than the manual noise reduction option), a new Adobe DNG file is created based on the original raw capture. By contrast, with the latest update to Camera Raw, you can apply Denoise to the raw capture non-destructively, without the need to create a DNG file. Assuming Lightroom Classic is updated to match this workflow, the timing of using Denoise will be even less of an issue.

Of course, when you create a DNG file by applying Denoise to a raw capture in Lightroom Classic, existing adjustments will be incorporated with the new file. For example, if you convert an image to black and white and then apply Denoise, the DNG file created in the process will appear in black and white. However, the adjustments are still non-destructive, so for example you could later convert the black and white DNG file back to a color image by turning off the “B&W” treatment option.

While you can really use the Denoise feature at just about any point in your workflow, for images that I feel will benefit from Denoise I prefer to apply the adjustment as early in my workflow as possible. This is mostly a simple matter of the Denoise adjustment having a significant impact on the image, and therefore having a somewhat significant impact on my decisions about other adjustments. I therefore find it helpful to apply Denoise early in my workflow. I may apply some of the adjustments from the Basic section first to get a better sense of the overall potential for the image, but once I feel that the image has potential but would benefit from Denoise, I apply Denoise right away.

Today’s Question: I have separate workflows for my Lightroom Classic photos and my Photoshop images. They are effectively organized by the Lightroom catalog and a Bridge folder structure. I have an extensive keyword structure in Lightroom and love how quickly and easily I can find photos. But I haven’t been able to see an entire list of assigned keywords or find a way to use them in a search of the entire Bridge folder structure. Do you have any suggestions?

Tim’s Quick Answer: You can actually add all keywords from Lightroom Classic as persistent keywords in Adobe Bridge, so that you’ll have access all keywords in both applications.

More Detail: I should point out right from the start that I don’t normally recommend using both Lightroom Classic and Adobe Bridge, due to the risk of confusion and metadata mismatches. But if you are working with completely different groups of photos with each application (or are extremely familiar with how these applications work), it can be done.

In this case I’ll assume that the two sets of photos are completely separate, even if that’s not the case, because the idea makes me feel more comfortable. But I digress.

Adobe Bridge will show you the keywords assigned to images in the current location, or for the currently selected image, for example. But Bridge also includes the concept of “persistent” keywords, which appear on the Keywords panel even if they have not been assigned to any images. This is similar to the Keyword List in Lightroom Classic.

If you’d like to make your full Keyword List from Lightroom Classic in Bridge, you can export from Lightroom Classic and import to Bridge.

To get started, in Lightroom Classic go to the Library module and from the menu choose Metadata > Export Keywords > Exclude Keyword Tag Options. In the dialog that appears you can enter a meaningful name for the exported file, and choose a convenient location to save it.

Once you’ve exported the keywords from Lightroom Classic, go to Bridge and click on the panel popup menu (the three horizontal lines) on the right side of the tab for the Keywords panel. From the popup menu choose Import (or choose “Clear and Import” if you want to clear out all persistent keywords from the Keywords panel and replace them with the keywords from Lightroom Classic). Navigate to the location where you saved the keyword export from Lightroom Classic, select the file you exported, and click the Open button. Note that importing keywords into Bridge in this way will not cause any existing keywords to be removed from your images, even if you used the “Clear and Import” option.

At this point you will have the full keywords list from Lightroom Classic available on the Keywords panel in Bridge. Just keep in mind that these lists won’t stay synchronized automatically. Therefore, if you want to update the lists I recommend adding keywords in Lightroom Classic and then repeat the import process in Bridge using the “Clear and Import” option.

Today’s Question: Please mention that the color labels of an image in Bridge do NOT correspond to the color labels in Lightroom Classic (dear Adobe: please fix this) and the color labels of an image in both images and folders are not visible outside of their respective software.

Tim’s Quick Answer: Actually, this issue can easily be fixed (mostly) by updating the color label definitions.

More Detail: The problem with color labels in software such as Bridge and Lightroom Classic is that they aren’t really color labels at all. I mean, they look like colors, but really they are simply represented by text in a metadata field, similar to keywords. The real problem that is the basis for today’s question (or request) is that Adobe used different default text for color labels in Bridge versus Lightroom Classic.

A red color label gets the word “Select” in Bridge, while it gets the word “Red” in Lightroom Classic. Similarly, yellow is “Second” in Bridge and “Yellow” in Lightroom Classic. As you may have realized, in Lightroom Classic the color label definitions are logical, and in Bridge they are unique to whatever Adobe employee defined them in the first place.

But you can change those definitions. If you had been using Bridge and switch to Lightroom Classic, you can change the color label definitions to the Bridge defaults by going to the Library module and choosing Metadata > Color Label Set > Bridge Default from the menu. Note, however, that if you change the definitions, any images with color labels that don’t match the definitions will appear as a white color label rather than the color you had actually assigned.

Similarly, you can change the color label definitions in Bridge. In the Preferences dialog go to the Labels and Ratings tab, where you can change the definitions for the color labels in the Label Options section. For example, you could update these to the names of the colors as used in Lightroom Classic.

It is important to keep in mind, however, that if you assign color labels in Bridge for photos that are already imported into your Lightroom Classic catalog, those color label updates won’t appear in your catalog. Rather, you’ll see a metadata mismatch. My recommendation, however, is to never update metadata outside of Lightroom Classic for photos that are being managed with a Lightroom Classic catalog.

Similarly, color labels assigned in Lightroom Classic will not appear in Bridge unless you have saved metadata out to the source images, in addition to having those updates saved in the catalog. This can be enabled by turning on the “Automatically write changes into XMP” checkbox on the Metadata tab of the Catalog Settings dialog, for example.

If you’ve struggled with restoring order to your workflow and catalog in Lightroom Classic, I have an online workshop next month that can help you tidy up your workflow and better understand how Lightroom Classic works. For a limited time you can get the full workshop experience (including getting answers to your questions) for just $59. Get all the details here:

https://www.greylearning.com/courses/online-workshop-cleaning-up-your-mess-in-lightroom-classic-january-2025

Today’s Question: I’ve had the idea that I need to keep external drives connected to my laptop all the time when I’m at home. But do I? Similarly, do I need my backup drive connected all the time or only at those times when Carbon Copy Cloner is scheduled to back up?

Tim’s Quick Answer: Out of an abundance of caution, I prefer not to keep external hard drives connected to the computer unless they are needed.

More Detail: While it is perfectly reasonable to keep external hard drives connected to your computer at all times, so you have access to the data on those drives at any time, I prefer to only keep external hard drives connected when they are actually needed.

Admittedly, this is a habit born out of what some may consider an extreme abundance of caution. Part of the concern, for example, is that if you keep all hard drives connected at all times and there is a severe power surge or lightning strike, you may have a situation where all drives are damaged at the same time and you don’t have a backup to recover from. This is obviously not a highly likely event.

In general, it is safe to keep hard drives connected to the computer at all times. I just prefer to take a more cautious approach and only connect the drives I need when they are needed. That could include connecting drives in time for a scheduled backup, or connecting drives all day long when you’ll be working with your photos, for example.

Keep in mind, by the way, that with Lightroom Classic you don’t need to have your source photos available to be able to review and update metadata, based on having built previews of your photos. If you build Smart Previews you can even work in the Develop module when the source photos are unavailable due to a hard drive being disconnected.

To be sure, this isn’t an issue I would stress about. To me it is just a matter of trying to maintain the best habits to minimize the risk of data loss. Therefore, I only connect drives when I need them. For example, I never connect all backup drives and the source drive at the same time, instead backing up to a single drive without other backup drives connected during that backup.

Today’s Question: I have installed the beta version of Photoshop so I can explore the new features there. But now when I send an image to Photoshop from Lightroom Classic it is opening in the beta. Is there a way to edit in the non-beta version without uninstalling the beta?

Tim’s Quick Answer: Yes, you can designate which installed version of Photoshop you want to use for editing on the External Editing tab of the Preferences dialog in Lightroom Classic.

More Detail: You can have more than one version of Photoshop installed at a time, including the public beta version if you’d like to test out new features that are still in development. Fortunately, Lightroom Classic includes an option for you to choose which version of Photoshop you’d like to use when using the “Edit In” command to send an image from Lightroom Classic to Photoshop.

To change this setting, first bring up the Preferences dialog in Lightroom Classic by choosing Edit > Preferences on Windows or Lightroom Classic > Preferences on Macintosh. Go to the External Editing tab, and then choose the desired version of Photoshop from the “Photoshop version” popup in the top section. In this case, for example, you could choose “Adobe Photoshop 2025” from the popup instead of “Adobe Photoshop (Beta)”.

Once you’ve changed the setting, anytime you use the Photo > Edit In command to send an image to Photoshop, the version you selected in Preferences will be the version of Photoshop your image is opened in.

Today’s Question: I’ve been exploring the addition of a vignette effect to photos, and so far I’m happy with the results. However, no matter what setting I use for the Highlights slider I’m not seeing an effect. What is this slider supposed to do?

Tim’s Quick Answer: The Highlights slider for the vignette adjustment in Lightroom Classic, Lightroom, and Camera Raw, enables you to have bright highlights (such as the sun in the frame) overpower the vignette effect rather than being darkened down unnaturally.

More Detail: The vignette effect adjustment in Lightroom Classic, Lightroom, and Camera Raw enables you to more or less mimic the behavior of a natural lens vignette, along with other creative possibilities. The Highlights adjustment enables you to make the vignette effect more realistic in this context.

When a lens creates a vignette effect it is the result of light falloff around the edges of the frame, causing those areas to appear darker than the central area of the image. However, if there is a very bright light source, such as the sun, near the edge of the frame, that will overpower the vignette effect so that the area appears bright, with little or no visible vignette. The Highlights slider enables you to mimic this effect.

The Highlights slider is only available when you have selected either “Highlight Priority” or “Color Priority” for the style option, not with “Paint Overlay”. The Highlights slider is also only available when you have used a negative value for the vignette effect, resulting in a darkening rather than lightening of the perimeter of the photo.

In addition, the Highlights slider will only have an obvious effect if you have very bright areas (such as bright lights or the sun) in the area of the image that is being darkened by the vignette effect. In that case, increasing the value for Highlights will cause bright areas to overpower the vignette effect, so they are not darkened (or not darkened as much) as areas that are not as bright. This can create a more natural vignette effect in photos that have bright areas toward the perimeter.