Category: Ask Tim Grey

Today’s Question: If pixel per inch (ppi) resolution doesn’t matter for the digital display of photos, wouldn’t saving at 300 ppi create a larger file than with 72 ppi?

Tim’s Quick Answer: No. The pixel per inch resolution setting for an image has absolutely no impact on the file size.

More Detail: The total number of pixels in the image combined with the file type and related settings determine the file size for an image. The ppi resolution is simply a metadata setting used for determining the output size of an image when it is printed.

As may have been made abundantly clear by the number of questions I’ve addressed recently related to resolution in general and ppi resolution in particular, clearly this is a topic that leads to confusion.

The pixel per inch resolution is simply a way to explain the overall pixel dimensions in an image in a way that is intended to be more clear. For example, I think most people would agree it is more meaningful to say that an image is 10-inches wide by 10-inches tall rather than that the image consists of 3,000 by 3,000 pixels. But in order to say that an image is 10-inches across, we would need to specify the pixel density, which is what the ppi resolution provides. So instead of saying the image is 3,000 by 3,000 pixels, we can say the image is 10-inches by 10-inches at 300 pixels per inch. Both are saying the exact same thing in terms of pixel dimensions, just using different terminology.

Changing the pixel per inch resolution for an image will not affect the file size, all other things being equal. For example, let’s assume an image that is 1,000 by 1,000 pixels, in the 8-bit per channel bit depth, saved as a TIFF file without compression. The file size will be about 3MB. If you change the ppi resolution to 300 ppi, the file size is still 3MB because it still contains the same number of pixels. If you change the ppi resolution to 1,000,000 ppi the fie size is still 3MB because it still contains the same number of pixels.

Just remember that the ppi resolution simply provides a way for you to translate a set number of pixels to a set number of inches on the printed page. The ppi number is just a metadata value, intended to provide helpful translation information but unfortunately leading to confusion for many photographers.

Today’s Question: You suggested not saving an image as a JPEG if it is intended for print, because of the risk of compression artifacts. But what exactly are compression artifacts and what would they look like in the image or the print?

Tim’s Quick Answer: The compression artifacts for JPEG images appear as a grid pattern across the overall image, which is generally somewhat easy to spot if you use a high zoom setting especially on a JPEG image saved with a moderate quality setting.

More Detail: JPEG images use a compression method that is “lossy” meaning that actual pixel values are altered in order to reduce the file size. By contrast, images saved with a lossless compression method will preserve all pixel values precisely, while still reducing the file size. The advantage of lossy compression is that the file can be much smaller, but the disadvantage is the loss of image quality.

The way JPEG files compress image data is to break the image into blocks of pixels and then simplify the pixel data within each block. For example, that might mean a block of 8×8 pixels or 16×16 pixels. The pixel data within each of those blocks is compressed without evaluating the pixel values in neighboring blocks.

Because each block of pixels is compressed in isolation, the changes in one block won’t necessarily align well with the changed pixel values in a neighboring block. This can create an underlying grid pattern in the image that in some cases can be quite visible, both for images shared digitally and those that are printed.

The visibility of JPEG compression artifacts is greater when the image is saved at a relatively low quality setting. With some images, in fact, it may be very difficult to see the compression artifacts if the quality was set to a high value.

To get a better sense of what these JPEG artifacts look like, I recommend saving a copy of an image as a JPEG with the quality setting at the lowest value. For example, you can open an existing JPEG image in Photoshop, and then choose File > Save As from the menu. Specify a unique filename and storage location for this image, so you don’t confuse it with the original image. In the JPEG Options dialog set the Quality value to zero and click OK to save the image.

Next, open the image you just saved, and zoom in closely. You will see a very obvious grid pattern in the image. In fact, at such a low quality setting you may find that some blocks of pixels have been altered so that all pixels in the block (such as an 8×8 pixel block) have all been shifted to the exact same color.

Evaluating a JPEG image that has been saved at the lowest quality setting can help you get a better sense of what the JPEG compression artifacts look like. While these artifacts can be difficult to see on some images saved at a high quality setting, once you know what to look for you may still see artifacts in some areas of the image. Those artifacts, even if difficult to spot, can certainly translate to unwanted artifact patterns in the finished print, or for an image shared online.

Today’s Question: As a follow-up to your question about 16-bit versus 8-bit for derivative images created from a JPEG original, why not just use 8-bit per channel for all images that are sent to Photoshop rather than using a different setting for different images?

Tim’s Quick Answer: The primary reason to use the 16-bit per channel bit depth whenever possible for images that were captured at a high bit depth is to avoid posterization, which is the loss of smooth gradations of tone or color. This is of particular concern for black and white images or images that will require strong adjustments.

More Detail: One of the benefits of using raw capture with your digital camera is that you’re retaining the full capabilities of the image sensor, such as by maintaining high-bit data.

While we generally save our image files as either 8-bit or 16-bit per channel, cameras often capture images with bit depths in between these values. Many cameras capture at 10-bit or 12-bit for example, with top cameras supporting full 16-bit per channel bit depth.

The bit depth refers to the total number of possible tonal and color values in the image. A single bit is simply off or on, generally referred to as having a value of zero or one. With two possible values for each bit, you can use exponents to determine the total number of tonal and color values based on the bit depth.

For example, 8-bit per channel can be calculated as two raised to the power of eight, which equals 256. Since there are three channels in a color photograph, that means we can cube that value (256 to the power of three) to determine that an 8-bit per channel RGB image can contain up to 16,777,216 colors.

That is a relatively large number of color values, and in fact it is regarded as the approximate number of discrete color values that can be perceived by normal human vision. However, the picture is not so good when it comes to a black and white image. In that case the image would only support up to 256 shades of gray, which is not very many shades at all.

In addition, applying adjustments (especially strong adjustments) to an image can reduce the total number of tonal and color values represented by the image. The stronger the adjustments, the greater the risk that smooth gradations will no longer appear smooth.

Working in the 16-bit per channel bit depth provides much greater latitude for your images. For color images with 16-bit per channel data you will have up to more than 281 trillion possible color values. Even for black and white photos you would have up to 65,536 shades of gray available.

Even if you’re creating raw captures with a camera that only supports 10-bit or 12-bit analog-to-digital conversion, there are still potentially significant benefits to using the 16-bit per channel mode rather than downgrading to 8-bit per channel mode.

A 10-bit per channel capture can represent over 1 billion possible color values, or up to 1,024 shades of gray for a black and white image. A 12-bit per channel capture can represent over 68 billion possible color values, or up to 4,096 shades of gray.

I recommend keeping images in the 16-bit per channel mode unless the source image used to create a derivative image was captured in 8-bit per channel bit depth to begin with, as would be the case with a JPEG capture.

Today’s Question: If I send a JPEG to Photoshop from Lightroom Classic and want to create a copy rather than editing the original JPEG, I assume that I’m creating a 16-bit per channel image from the 8-bit per channel JPEG based on the External Editing settings in Preferences. If so, should I change that setting before sending a JPEG to Photoshop from Lightroom Classic?

Tim’s Quick Answer: My recommendation in this context is to keep the Preferences set to the 16-bit per channel option, but then convert the image to 8-bit per channel mode in Photoshop before saving the finished image.

More Detail: When you create a new file when sending a photo from Lightroom Classic to Photoshop, the new file is created based on the settings established on the External Editing tab of the Preferences dialog in Lightroom Classic. That means you’re either creating a Photoshop PSD or TIFF file, and that by default the new file will be set to a bit depth of 16-bits per channel (per component).

When you send a JPEG image with a bit depth of 8-bits per channel to Photoshop and the resulting PSD or TIFF file is set to a bit depth of 16-bits per channel, you’re creating a file that is twice as big as it needs to be, with no real benefit in terms of the quality of the derivative image you’re creating.

While it is possible to change the settings on the External Editing tab of Preferences before sending a JPEG image to Photoshop, I don’t recommend taking that approach. Put simply, you might change the setting before sending a JPEG image to Photoshop, and then forget to change the setting back to 16-bit per channel option before sending a raw capture to Photoshop. I therefore recommend keeping the setting at 16-bits per channel, which is the safest and preferred setting.

Instead, when you create an image in 16-bit per channel mode based on a source image that was only captured at 8-bits per channel, I recommend changing the bit depth for the derivative image in Photoshop before saving the final result. To do so, go to the menu in Photoshop and choose Image > Mode > 8 Bits/Channel.

This approach ensures that by default you’re creating derivative images when sending a photo from Lightroom Classic to Photoshop with a bit depth of 16-bits per channel, which provides greater latitude in terms of color and tonal values. You can then convert the derivative image to 8-bits per channel for images that were created based on an 8-bit per channel original. With this workflow, the worst thing that might happen is that you forget to convert an image created from a JPEG to the 8-bit per channel bit depth. That would just mean that the file was twice as large as it needed to be, but there’s no problem in terms of image quality. More to the point, taking this approach means you won’t inadvertently create a derivative image at 8-bits per channel for a source image that was 16-bits per channel.

Today’s Question: I can export my processed photos (from Capture One) as either JPEG or TIFF format, as well as DNG or PNG. Which format is preferable for printing?

Tim’s Quick Answer: When saving an image intended for print, I recommend saving as a TIFF file, because that will help ensure optimal quality for the finished image. I also recommend using the 16-bit per channel mode when exporting the TIFF image, assuming the source image was a raw capture or otherwise high-bit capture.

More Detail: The only format I strongly recommend against using when creating a derivative image for the purposes of printing a photo is the JPEG format. That’s because in almost all cases the JPEG format uses lossy compression, which means that even at a high setting for quality there will still be compression artifacts in the image. This can create a problematic pattern in the print, which can be avoided by using a different file format.

While not all printers support 16-bit per channel data output to the printer, I still recommend saving the derivative image as a 16-bit file to maximize the potential output quality. To be sure, as long as the image doesn’t need to be edited after creating the TIFF file, there is really very little benefit to saving this derivative image in the 16-bit per channel mode rather than 8-bit per channel mode. However, I prefer to err on the side of optimal print quality, and so recommend saving in the 16-bit per channel mode.

In addition, the TIFF file format is very widely supported by software and is recognized and supported by virtually all printing services. All things considered, in my view the TIFF file format is the best option to choose when saving a derivative image for printing.

Today’s Question: I have tagged many people in photos [with keywords in Lightroom Classic]. Now I want to search for certain people in the photos. I can find a single person, but I can’t seem to search for photos that contain multiple people. Is there a way to search for photos that contain two specific people?

Tim’s Quick Answer: You can search for photos that have keywords for two (or more) different people by using the Text search for the Library Filter Bar in Lightroom Classic, making use of the “Contains All” option.

More Detail: There are a variety of ways you can search for photos based on keywords in Lightroom Classic, including searching for keywords that represent the names of specific people who appear in a photo. In many cases when you specify multiple criteria for a search in Lightroom Classic, the search is conducted based on an “or” option. For example, if you search for keywords of “Paris” and “London”, the search result would include photos that have either Paris or London as keywords.

If you want to search for only those photos that include two (or more) keywords, such as to find photos keyworded as including more than one person, you can use the “Contains All” option for the Text tab of the Library Filter Bar.

To get started, navigate to the location (such as a folder, or even the All Photographs collection) that you want to search. Then go to the Library Filter bar above the grid view in the Library module. If the Library Filter Bar isn’t displayed, you can choose View > Show Filter Bar from the menu.

On the Text tab of the Library Filter Bar, select “Keywords” from the first popup to search based on keywords in metadata. From the second popup choose “Contains All”, which will cause the search result to only include photos that contain all the keywords you specify. In the text box to the right of the two popups you can then enter the applicable keywords (in this example the full keywords representing the names of the people), with the keywords separated by commas.

The result will be only photos that include all the keywords you entered into the text field, along with any other filter criteria you may have specified from the other tabs, such as to also filter based on star ratings.

Today’s Question: I have a follow-up question on your recent post regarding 4K monitors. I love my 27″ 4K monitor but wondered how important the color gamut is. My monitor supports 100% of the sRGB color space. Is it worth upgrading to one with the Adobe RGB specification?

Tim’s Quick Answer: A monitor with a wide color gamut can be helpful in terms of providing a more refined view of the colors in your images and a more accurate preview of what a print will look like. However, in general I would say that it is not critically important to have wide-gamut support in a monitor display.

More Detail: Virtually every monitor available will support 100% (or nearly so) of the sRGB color space. This is in part because the sRGB color space itself was created with the specific intent to encompass the color range supported by a typical monitor display. A smaller percentage of monitors support a wider color gamut, such as those that support all (or most) of the Adobe RGB color space, which is a bit larger than the sRGB color space.

By the way, literally zero monitors support the even larger ProPhoto RGB color space, and no monitor ever will. I can say that confidently because the ProPhoto RGB color space is so large that it actually includes colors that are beyond the visible spectrum.

It can certainly be advantageous to have a monitor that is capable of displaying a wider range of color values. After all, if the display can’t present all the colors that appear in an image you’re reviewing, you aren’t getting a completely accurate display of the color information in the image.

That said, many images are only shared digitally, such as on a monitor display or with a digital projector. In these cases, the sRGB color space would be more than adequate for evaluating your photos, especially considering that the vast majority of displays and projectors are only going to support the sRGB color space to begin with.

If you print images on a regular basis, and if you are particularly critical of the nuance of colors in the image, then a display that can present a larger color gamut can certainly be helpful. Whenever possible I do suggest opting for a display that supports 100% (or nearly so) of the Adobe RGB color space, because that is a better match for photos that will be printed.

In my own workflow, for example, I don’t tend to print images all that often. Most of my work focuses on digital sharing of photos and on video production work. Therefore, a wide-gamut display isn’t a high priority for me personally. But for photographers with a strong focus on printing their photos, a display with a wider gamut can be helpful. I’m not sure I would replace a perfectly good monitor just to gain support for the Adobe RGB color space, but it is certainly a specification I would consider when you do decide to purchase a new display.

Today’s Question: When I send a Raw file from Lightroom Classic to Photoshop via Edit In, it opens in the main Photoshop window rather than Camera Raw. What am I doing wrong?

Tim’s Quick Answer: You’re not doing anything wrong, as this is exactly the expected behavior. In this workflow the Develop module in Lightroom Classic is taking the place of Camera Raw in Photoshop.

More Detail: When you open a raw capture in Photoshop it needs to be processed into a “normal” image format rather than a raw capture format so it can be edited directly in Photoshop. When opening a raw capture with Photoshop that means the image is opened in Camera Raw as an intermediate step. When sending a raw capture from Lightroom Classic the use of Camera Raw is not necessary, because the raw processing is handled by the Develop module.

In effect, you can think of Camera Raw in Photoshop and the Develop module in Lightroom Classic as being the exact same thing. The interface is a little different, and sometimes they get slightly out of sync based on upgrade timing from Adobe, but they are effectively the same.

When you send a raw capture from Lightroom Classic to Photoshop it is processed by the Develop module as though you were opening via Camera Raw. That results in an image with the initial processing completed being opened in Photoshop. If you simply choose File > Save from the menu in Photoshop the image will be saved as a Photoshop PSD or TIFF file based on the settings established on the External Editing tab of the Preferences dialog in Lightroom Classic.

Note that while you are working with the image in Photoshop it is possible to access the Camera Raw adjustments by choosing Filter > Camera Raw from the menu. However, in general I would suggest just saving those additional adjustments for when you get back to Lightroom Classic after editing the image in Photoshop and saving the result. You can then use the Develop module to further refine the image as needed.

Today’s Question: I’ve bought into the 72 ppi [pixel per inch] misinformation for 20 years. Curious if it was EVER true. Since we can’t know what displays our clients will use, what should we do for a photo in an email or on a website? Should I just pick a number around 200 [for ppi resolution] and hope for the best?

Tim’s Quick Answer: The pixel per inch (ppi) resolution is irrelevant for images that will only be displayed digitally, as only the actual pixel dimensions really matter in that context. The 72 ppi value was actually accurate for the original Macintosh 9-inch display, which featured a resolution of 512×342 pixels (not a lot of pixels!).

More Detail: Today’s question is a follow-up to my answer from the December 12th newsletter where I addressed the general topic of pixel per inch (ppi) resolution for digital images. As noted in that answer, the ppi resolution is only a factor when printing. Even then, it is really there for convenience. Referencing a ppi resolution enables you to describe a print size in more familiar terms. Instead of saying that you need to resize an image to 2,400 pixels by 3,000 pixels, you can say that you need to resize the image to 8-inches by 10-inches at 300 pixels per inch.

While the ppi resolution really doesn’t mean anything for images intended to be displayed digitally, that isn’t to say you should necessarily completely ignore this value when resizing an image for digital sharing.

I most certainly don’t suggest setting the image to a resolution of 72 ppi, since that doesn’t align with any method for sharing images today. I also don’t recommend the 96 ppi value that had similarly become commonly used with the (false) notion that Windows computers used a display resolution of 96 ppi while Macintosh computers used 72 ppi.

I think the best default value for the ppi resolution for images that will be shared digitally is a resolution that would be suitable for printing. That way if the image does get printed by a client, for example, it would already be configured at a reasonable setting.

While output resolution varies depending on printing equipment and other factors, a good general value is 300 ppi. So, for images that are going to be shared digitally, the ppi resolution doesn’t really matter at all. But you may as well set it to something like 300 ppi by default, since that is a commonly used resolution setting when an image is printed.

Today’s Question: You referred to using a 4K monitor as your “primary display”, which I assume means you are using more than one monitor on your computer. Is this something you generally recommend, or do you have unique needs for multiple displays that wouldn’t apply to most photographers?

Tim’s Quick Answer: I do find it very helpful to have two monitor displays and recommend that just about anyone consider taking this approach. Two displays can be helpful in general when working on a computer, but I also find two displays particularly helpful when working in Photoshop, and to some extent helpful in Lightroom Classic.

More Detail: To be sure, a big part of why I find it helpful to have two (or more) monitor displays is that I often have a lot going on when I’m working on my computer. That is especially true when I’m presenting online, for example, when I’m sharing my primary screen with viewers but also monitoring the broadcast software, watching for questions from viewers, and more, all on my secondary display.

But even when focused on my photography workflow, I find two displays to be very helpful. In Photoshop, for example, I love being able to put all the panels on my secondary display while only having the general Photoshop interface and the image I’m working on visible on my primary display. This provides much more space for the image I’m focused on.

While I don’t use dual displays as often in Lightroom Classic, this is something that is possible and that can be helpful. Lightroom Classic supports having a secondary window on a second display, though the features are a little limited. However, this does make it possible, for example, to view a grid of all images you’re currently browsing on the secondary display while focusing on the current image in the loupe view on your primary display.

So, yes, I absolutely think using two (or more) monitor displays can be very helpful and would certainly recommend that photographers consider this approach. For example, if you are considering getting a new display you could keep the old display so you can connect both and test out the benefits of multiple monitors for yourself.