Category: Ask Tim Grey

Today’s Question: If you print an 8×10, say, whose resolution matches your printer’s maximum resolution, the print should look good. What happens if your image file has significantly higher resolution than the printer’s capability? Does the image suffer in any way? (I assume it’s not benefitted. Is it?)

Tim’s Quick Answer: If the image contains more information than the printer needs to produce the given print size, the image data will be scaled down as needed. In general this won’t produce any significant degradation in image quality, although that “extra” resolution won’t provide a benefit either.

More Detail: Different printing methods involve different requirements in terms of image data, which translates into total pixel count. In some cases there is a specific amount of information required for a given print size, such as with a photo inkjet printer. In other cases, such as with offset press printing, the requirement isn’t quite as specific, and so there is generally a range of acceptable image resolutions to use.

Ultimately, the pixel per inch (ppi) resolution you set for an image is simply shorthand of sorts to help describe the total number of pixels in the image. For example, if we assume a print size of 10 inches on the long edge, and a photo inkjet printer that renders the output at 360 pixels per inch, then we know that the image file needs to be 3,600 pixels on the long edge to achieve optimal image quality.

If we send an image that has more than 3,600 pixels on the long edge, the printer will scale down the image data accordingly. If we send an image to the printer that has fewer than 3,600 pixels on the long edge, the printer will scale down the image data accordingly.

The alternative, of course, is to scale the image data to the optimal value before printing, such as within Photoshop. In other words, with this type of workflow we need a specific amount of data for printing at a given size. Our option is to let the printer scale the image data or to do so before printing with software such as Photoshop.

When it comes to final print quality then, the real issue here is which software will do a better job of scaling the image data. In the early days of photo inkjet printing there was a significant difference. Scaling the image in Photoshop before printing generally produced a print of much higher quality than if you started with an image at the “wrong” size and let the printer software perform the scaling.

Today, however, printer software has improved to the point that the differences are quite minimal. I still personally prefer to resize my images with an advanced software tool such as Photoshop. But the difference between resizing in Photoshop and letting your printer do the resizing will generally be relatively minimal, thanks to improvements over the years in the software that controls modern printers.

Note, by the way, that different printers render the image at different resolution values. Many photo inkjet printers use a value of 360 pixels per inch, but many others use slightly lower or higher values. An increasing number of photo inkjet printers are now available that render at 720 pixels per inch, for example. It is therefore a good idea to obtain information related to your specific printer before choosing how to scale your images.

Today’s Question: Is it necessary to save a selection [in Photoshop] if I’m going to create a layer mask based on the selection? Wouldn’t saving the selection in this case be somewhat redundant?

Tim’s Quick Answer: In general I would say that it isn’t necessary to save a selection using the “Save Selection” command if you’re going to create a layer mask based on that selection. After all, the layer mask also represents what is essentially a saved selection.

More Detail: However, there are situations where you may want to save a selection.

For example, if you will be building up a somewhat complicated selection in a series of steps, it can be helpful to save a series of selections and then merge those together into the final selection. In addition, you may find that in some cases you apply a variety of adjustments directly to a layer mask, causing changes compared to the original selection you used as the basis of that layer mask. In this type of situation you may want to save the initial selection before using that selection as the basis of a layer mask.

For most photographers and in typical workflow scenarios, however, I would say that it probably isn’t necessary to save a selection if you’re simply going to be using that selection as the basis of a layer mask. Of course, it is also worth noting that a saved selection won’t significantly increase the file size, so there isn’t significant harm in erring on the side of caution and saving selections as part of your master image files.

In those cases where you do decide to save a selection, you can simply choose Select > Save Selection from the menu to initiate the process. Enter a name for the selection in the Save Selection dialog, and click OK to save the selection as an alpha channel. As long as you then save the image as a Photoshop PSD or TIFF file, the saved selection will be included as part of the file.

Today’s Question: Should the XMP checkbox in the Catalog Settings dialog [in Lightroom] be checked at all times?

Tim’s Quick Answer: In my opinion, yes, it is best to have the “Automatically write changes into XMP” checkbox turned on. This option can be found on the Metadata tab of the Catalog Settings dialog in Lightroom.

More Detail: By default, Lightroom only saves metadata updates for your photos into the Lightroom catalog. I prefer to also have standard metadata fields updated in the image files for my photos. This provides two basic benefits. First, with this option turned metadata updates will be visible in other applications (such as Adobe Bridge) instead of only being visible within Lightroom. In addition, enabling this option provides a real-time backup of most of the metadata updates you apply.

Note that enabling this option will cause metadata updates to be saved for all supported image file formats in Lightroom. For non-RAW images (such as JPEG, TIFF, or DNG files) the actual image file will be updated. For proprietary RAW captures the updates will be written to an XMP “sidecar” file next to the RAW file.

If you apply metadata updates to a large number of photos all at once, having the option to automatically save metadata to your photo files can result in degraded performance. However, to me the benefits of having this option turned on more than makes up for any potential performance loss.

It is also important to keep in mind that not all metadata will be saved when you enable this option. Lightroom-specific features such as pick and reject flags, collections, Develop history, and virtual copies, will only be saved to the Lightroom catalog, even with the option to save metadata to your image files enabled.

Today’s Question: If I have several images captured under the same basic conditions with the same camera settings, what is the easiest way to apply the same adjustment to all of the images in Lightroom?

Tim’s Quick Answer: There are a variety of options available to accomplish this task, but I would suggest that synchronizing the adjustments in real time with the “Auto Sync” feature in Lightroom’s Develop module would be the easiest approach.

More Detail: The process of applying the same adjustments to multiple images in Lightroom is quite simple. When you want to apply those same adjustments in real time to multiple images, the Auto Sync feature provides a good solution.

The first step is to select the multiple images you want to apply the same adjustments to. You can, for example, click on the thumbnail for the first image and then hold the Shift key on the keyboard and click on the thumbnail for the last image, which will cause all images in between to be selected as well. You can also add or remove images to or from a selection by holding the Ctrl key on Windows or the Command key on Macintosh while clicking on the thumbnail for an image.

Once you have selected the images you want to apply the same adjustments to, you can choose which image you want to use as the basis of your adjustments. To do so, simply click on the thumbnail for the image itself (not the “frame” that surrounds the image) to make that the active image.

Next, enable the Auto Sync feature by clicking the toggle switch on the left side of the Sync button on the right panel in the Develop module in Lightroom. This button looks something like a light switch, and when it is turned on all adjustments you apply will be synchronized to all of the selected images.

At this point you can simply apply adjustments to the current image in the Develop module. Because you have enabled Auto Sync and have selected multiple images, all adjustments will synchronize to all of the selected photos in real time.

I do recommend turning off the Auto Sync feature when you’re finished, just to make sure you don’t accidentally apply further adjustments to the same selected images when you intended to focus on a single image again.

Today’s Question: I am embarrassed to say that I forgot to change the time on my camera during a recent trip, so all of my photos show the wrong capture time. Is there a way to fix this in Lightroom?

Tim’s Quick Answer: Yes, you can very easily correct a time zone discrepancy for your photos in Lightroom using the Edit Capture Time command found on the Metadata menu.

More Detail: For situations where the capture time error is simply due to having neglected to change the time on your camera when changing time zones, the correction is quite simple. First, navigate to the location where the affected photos are stored, and then choose Edit > Select All from the menu to select all of the photos in that location.

You can then choose Metadata > Edit Capture Time from the menu to bring up the Edit Capture Time dialog. Choose the second option in the “Type of Adjustment” section of the dialog, which is labeled “Shift by set number of hours (time zone adjust)”. Then, in the New Time section, choose the applicable number of hours you need to shift the images by from the popup at the far right. Keep in mind that you can choose a positive or negative value depending on the direction of the required shift.

When you select a number of hours to adjust the time by, the capture time for the currently active image will be presented, along with the updated time based on the correction you’ve selected. This enables you to validate that you have selected the correct number of hours to adjust the capture time by. When you have confirmed that the setting is correct, you can click the Change button to apply the adjustment. Keep in mind that this action can’t be undone, so if you make an error you’ll have to apply a new adjustment to the capture time to compensate.

It is also worth noting that by default Lightroom will only update the capture time for your images within the Lightroom catalog. If you want to save the changes to the actual image files, you’ll need to enable two options in the Catalog Settings dialog for the current catalog.

First, you’ll need to enable the “Automatically write changes into XMP” checkbox on the Metadata tab in the Catalog Settings dialog, so that Lightroom will save metadata updates to the image files in addition to saving those changes to the Lightroom catalog.

In addition, to enable updates to the capture time you’ll need to enable the “Write date or time changes into proprietary raw files” checkbox so that the metadata for RAW captures will be updated for those files, in addition to updating the Lightroom catalog.

Today’s Question: I created a selection in Photoshop for a JPEG capture, and saved that selection so I could put it to use again in the future. When I choose the Save command from the File menu, however, Photoshop prompts me to save the image as a Photoshop PSD file. I just want to save the updates to the JPEG image. Is that not possible?

Tim’s Quick Answer: No, it isn’t possible to save a JPEG image with a saved selection. Saved selections (among a variety of other features in Photoshop) can only be included with images saved as either a Photoshop PSD file or a TIFF image.

More Detail: When you open any supported image type (such as a JPEG image) in Photoshop, you can make full use of all of the available features within Photoshop for that image. So, for example, after opening a JPEG image you can save selections, add adjustment layers, and much more.

However, in order to save some of the advanced features of Photoshop as part of an image file, you need to use a supported image file format. A JPEG image, for example, doesn’t support layers, layer masks, saved selections, and other advanced features of Photoshop.

While you can use these various features with a JPEG image (or other supported image formats), that doesn’t automatically mean you can save the image in the same file format with all of the advanced features included.

JPEG images don’t support alpha channels, which are required to support the option to save selections as part of an image in Photoshop. The reason Photoshop is prompting you to save the JPEG as a PSD image is that you have made use of features that the JPEG file format doesn’t support.

So, if you want to retain your saved selections or other advanced features, you’ll need to save the image as a Photoshop PSD file or as a TIFF image.

Today’s Question: Does the Lightroom backup for the catalog also backup your photos? If not is there a way to accomplish this?

Tim’s Quick Answer: No, the Lightroom catalog backup feature does not backup your photos. While it would be possible to backup both your photos and the catalog using the “Export as Catalog” command, I recommend using a different solution for backing up your photos.

More Detail: When you use the backup feature in Lightroom, you are only backing up the Lightroom catalog, not your photos. In other words, you’re backing up the information about the photos and not the photos themselves.

As noted in yesterday’s Ask Tim Grey eNewsletter, there are some benefits to using the Lightroom catalog backup feature for backing up your catalog, including the option to check the integrity of the catalog and optimize the catalog. Therefore, it is a good idea to use the Lightroom catalog backup feature even if you have another backup solution that is also backing up your catalog.

For your photos you’ll need a different backup solution. I personally prefer a “synchronization” approach to backing up my photos and other data, which is covered in the “Backing Up with GoodSync” video training course in the GreyLearning library. If you’re not a GreyLearning subscriber you can purchase this individual course at a discounted rate using this link:

http://timgrey.me/greysync14

In theory you could also use the “Export as Catalog” command to backup both your Lightroom catalog and your photos in a single process. However, to make this approach useful you would need to export (and therefore copy) your entire catalog of photos. That could obviously require considerable time. Therefore, I only recommend using the “Export as Catalog” feature as a backup option when you need a one-time solution for copying your Lightroom catalog and photos to a different location, or for backing up everything in one overall process. For an ongoing backup solution I recommend something a bit more streamlined, such as the synchronization approach referenced above.

Today’s Question: If I’m backing up the drive with all my images and Lightroom each night to a cloud site and multiple external hard drives, is there an advantage to backing up the Lightroom Catalog in Lightroom? It can be time consuming and if my daily back up is providing the same level of “protection,” what’s the value?

Tim’s Quick Answer: The key advantage to using Lightroom to backup your catalog in addition to any other backups you may be performing is that Lightroom enables you to check the integrity of your catalog and optimize the catalog as part of the backup process.

More Detail: Obviously if you have an excellent backup workflow that provides you with redundant copies of your Lightroom catalog, then the option within Lightroom to backup the catalog may seem redundant. At least in concept there is no need to have a Lightroom version of your catalog backup if you have another perfectly good backup to restore from in the event of a problem.

However, Lightroom also includes the option to check the integrity of your catalog and to optimize the catalog as part of the catalog backup process. Both options are available as checkboxes within the “Back Up Catalog” dialog in Lightroom.

The “Test integrity before backing up” option will cause the catalog to be checked for any problems that could ultimately lead to a corrupted catalog file. I highly recommend employing this option whenever you backup your catalog from Lightroom, to help minimize the risk of a corrupt catalog that could cause data loss.

The “Optimize catalog after backing up” option will cause Lightroom to perform some housekeeping chores for your catalog. You can also find this option on the File menu if you want to optimize the catalog outside the context of backing up your catalog. Optimizing the catalog with this process can help improve overall performance. Therefore I recommend performing this task every time you backup your Lightroom catalog (or about once a month if you aren’t using the Lightroom catalog backup feature), or anytime you notice degraded performance in Lightroom.

It is also worth noting that it is a good idea to backup your Lightroom catalog to a location that is on a separate storage device from your original catalog. For example, if you store your Lightroom catalog on the internal hard drive on your computer, you can store the backup copies on an external hard drive.

Today’s Question: What is the difference/advantage of changing a file to sRGB via “assign profile” and “convert to profile” [in Photoshop]?

Tim’s Quick Answer: If you want the colors in the photo to remain unchanged (to the extent possible), you should use the “Convert to Profile” command. If you want to change the appearance of colors in the photo based on a profile, you would use the “Assign Profile” command. In general I would say that photographers today are therefore more likely to want the “Convert to Profile” command, and not the “Assign Profile” command.

More Detail: There are two basic reasons you might want to change the color space associated with a photo. The first (and most common for photographers these days) is to change a photo to a different color space based on a specific output scenario. For example, when preparing a photo to present online, it can be a good idea to convert to the sRGB color space to help ensure more accurate color for the photo being shared. In this type of scenario you want to maintain the same appearance of colors in the photo.

The other scenario is one where you actually want to change the appearance of colors based on a profile. For example, if you scan a slide or negative, you could use an ICC profile for the scanner to apply an automatic correction to the scanned image. The scanner profile would then be used as the basis of a change in color appearance for the photo to make the resulting colors more accurate.

These days I find that many photographers have a need to convert a photo to a different profile for reasons related to how that photo is being shared. In this type of situation you want to maintain the color appearance of the photo, so the “Convert to Profile” command would be appropriate.

Only when you actually want to change the appearance of a photo based on an ICC profile should you use the “Assign Profile” command. These days I would say that most photographers are therefore probably not using the “Assign Profile” command much, if at all.

Today’s Question: Please help me understand the difference in field of view (really image size) between an ASP-C lens on a crop frame body and a full frame lens on a full frame body.

For example, would a 11-16mm APS-C lens set to 16mm mounted on my camera body with a 1.6X crop factor have the same angle of view as a Canon 16-35mm full frame lens set to 16mm mounted on a full frame body? Would both images be the same size?

I understand about multiplying the focal length times the crop factor when switching a lens between bodies. I don’t understand the difference, if any, in image size between a full frame lens and a crop frame lens when each is mounted on its respective body and set to the same focal length.

Tim’s Quick Answer: A 16mm lens on a “cropped” sensor will not provide the same field of view as a 16mm lens mounted on a “full frame” sensor. The field of view of the actual lens remains the same in both cases. However, because the smaller sensor is capturing only a portion of the image circle projected by the lens, in this case the cropped sensor camera will produce a field of view equivalent to a 25.6mm lens (16mm X 1.6) on a full-frame camera, assuming a 16mm focal length lens in both cases.

More Detail: I think most photographers understand the basic concept of a “cropped” sensor. Because the 35mm film capture format became such a popular format, it is used as the basis for a great deal of photographic equipment. So we have “full frame” digital cameras that have an image sensor that is essentially the same size as a single frame of 35mm film. As such, with a “full frame” camera your lenses will provide the same field of view you may have come to expect when using a given focal length lens with a 35mm film camera in the past.

A camera with a “cropped” sensor is simply capturing a smaller area of the image circle projected by the lens. So while you aren’t actually getting any extra “zoom” factor from your lens, you are getting a smaller field of view that matches what a longer focal length lens would achieve with a full frame camera. So you’re getting a zoom effect without an actual optical zoom.

For example, on a camera with a 1.6X “cropping factor”, a 100mm lens would produce the same field of view as a 160mm lens on a full frame camera. You aren’t truly zooming, at least from an optical standpoint, but you are achieving a smaller field of view equivalent to that of a longer focal length lens.

An additional point of confusion can result from lenses that are specifically designed for “cropped” sensors. However, the only real difference here relates to the size of the image circle being projected by the lens. A lens designed for a cropped sensor camera generally can’t be used on a camera with a full-frame sensor, because the image circle projected by such a lens will not cover the full area of the image sensor on a full-frame camera.

The bottom line is that there is a relationship between focal length and field of view. However, the specific field of view achieved with a lens of a given focal length depends upon the size of the image sensor being used to capture the scene. Ultimately the real challenge here is in describing the behavior of a lens while talking about the focal length of the lens.

A great solution in my opinion would be for lenses to be described not on focal length but instead based on field of view. But again, that field of view depends upon the size of the image sensor used to capture an image, and many lenses can be used with cameras of varying sensor sizes. In other words, there isn’t really a simple way to describe the field of view of a lens unless you also refer to a specific sensor size.

It is worth noting, by the way, that whatever field of view you’re ending up with for a given sensor and lens focal length combination, in general you are making use of the full image sensor to capture that scene. Thus, while a smaller sensor doesn’t truly provide additional zoom for a given lens, it can still provide excellent image quality for that image with a smaller field of view. In other words, we are largely talking about semantics here. Once you’re using a given camera, you can simply focus on the field of view you want to obtain when making a decision about which lens to use.