Ask Tim Grey

Today’s Question: After working the master file in 16-bit, is it OK to convert the master file to 8-bit right before saving the master file as a Photoshop PSD?

Tim’s Quick Answer: My answer here would be “no”, in part because it would be necessary to also flatten the master image if you are going to convert it to 8-bit per channel mode.

More Detail: When you convert an image from 16-bit per channel mode to 8-bit per channel mode in Photoshop, the adjustments are also “scaled” to the 8-bit per channel mode. In other words, you lose the benefit of having worked in the 16-bit per channel mode in the first place.

Therefore, if you need to convert a layered image from 16-bits to 8-bits per channel, it is important to flatten the image.

As any photographer who has been reading my work for any length of time can probably appreciate, I prefer to retain as much information as possible in my master image file. That means I prefer not to flatten a layered master image in Photoshop, and I prefer to keep that master image in the 16-bit per channel mode.

If you want to convert a master image to the 8-bit per channel mode in order to reduce the file size, you would also want to flatten the image first to retain the benefit of the original adjustments you applied in the 16-bit per channel mode.

So, if you’re comfortable both flattening the master image and converting the result to the 8-bit per channel mode, then you can convert. If you’re not comfortable flattening the master image I would advocate for keeping that master image in the 16-bit per channel mode as well.

Today’s Question: I’ve been using the Wacom tablet with Photoshop CS6 and the pen responds to pressure.  With the download of Photoshop CC, there is not response to pressure. I may as well be using a mouse. Is there a fix?

Tim’s Quick Answer: You can either “force” the use of pen pressure to affect size or adjust the brush preset settings within the Brush panel in order to resolve this issue.

More Detail: With the brush-based tools within Photoshop that support pen pressure, there is a button on the options bar that enables you to force the use of the stylus pressure to adjust brush size. You’ll find this button at the far right of the Options bar for tools such as the Brush tool and the Clone Stamp tool.

If you don’t want to turn on this “universal” setting, you can also adjust the settings for individual brush presets using the Brush panel. For example, on the Shape Dynamics tab of the Brush panel you can set the Control popup for Size Jitter to “Pen Pressure”. This setting can be adjusted for each individual preset in the Brush panel, so if you want to always use the stylus pen for adjusting the brush size, the “universal” setting on the Options bar may be your better approach.

Today’s Question: I often need to switch from landscape to portrait in the crop tool in Lightroom [or Photoshop]. Is there an easy quick way to do that?

Tim’s Quick Answer: Yes! You can rotate the orientation of the crop box in Lightroom or Adobe Camera Raw by pressing the “X” key on the keyboard.

More Detail: Many photographers (myself included) find that they periodically want to rotate the crop box by 90 degrees, such as to rotate a horizontal crop box to a vertical orientation.

When working with the Crop tool within either Lightroom or Adobe Camera Raw, pressing the “X” key on the keyboard will rotate the orientation of the crop box between landscape and portrait. If you have selected a fixed aspect ratio for that crop, that aspect ratio will be retained. If you have not selected a fixed aspect ratio, whatever aspect ratio your current custom crop represents will be retained.

Today’s Question: Occasionally, I attach a screen grab to an email, usually PNGs directly from my Mac’s screen-grab commands. In one example the PNG’s file size is over 860KB versus the JPG version at 208KB. Are PNGs always so big, at about four times the size of equivalent JPGs?

Tim’s Quick Answer: PNG (Portable Network Graphics) files will generally be considerably larger than JPEG (Joint Photographic Experts Group) images, because PNG images use lossless compression compared to lossy compression for JPEGs. The specific results will vary depending on the image in question, but when file size is the priority the JPEG format is preferred over PNG.

More Detail: When sharing images, the JPEG file format is a popular option because it enables you to achieve relatively small file sizes. This small file size is achieved due to lossy compression, meaning some degree of image quality may be lost even at a high quality setting.

By comparison, the PNG file format uses lossless compression. As a result, image quality is preserved at the cost of a larger file size.

Of course, at a high quality setting the JPEG image will generally appear to have quality that is nearly the same as the same image saved as a PNG file. Therefore, the JPEG file format is generally superior for sharing images where file size is a concern, such as for online sharing.

In theory the PNG format would be preferred when image quality is the priority. However, in those cases it might also make sense to instead use the TIFF file format. The main reason I consider the PNG format to be important is that it supports transparency in the image. This isn’t generally a necessity for a photographic workflow, but for certain uses (such as in digital slideshows, on web pages, or in videos) that feature can be helpful.

Today’s Question: When a Curves adjustment is used to increase or decrease brightness in an image, some photographers drag the curve center point at a roughly 45 degree angle toward the top left to increase brightness or toward the bottom right to decrease brightness. Other photographers drag the center point vertically toward the top to increase brightness or vertically toward the bottom to decrease brightness. And the arrow keys also facilitate fine adjustment using this approach. The resulting tone curves are plainly different with each approach. Which is the best approach for overall image brightness adjustment?

Tim’s Quick Answer: There isn’t a single “correct” direction to drag an anchor point with the Curves adjustment. Rather, what is important is the specific relationship you’re defining between the “before” and “after” value for tonality. The optimal result will vary based on the specific image you’re working on.

More Detail: If you drag an anchor point directly upward (or downward) at the precise center of the curve, you will be applying an equal adjustment to the highlights and shadows in the image. If the anchor point is dragged out at a 45-degree angle toward the top-left, you will have a stronger effect on the highlights than on the shadows.

What ultimately matters here is the shape of the curve and the effect you want to have on the image. Keep in mind that what you’re altering with the curve is the relationship between the “before” and “after” values within the image. How you adjust the shape of the curve depends on how you want to adjust the tonal values in bright versus dark areas of the image.

It is also worth keeping in mind that in many (if not most) cases you will want to add more than one anchor point for the Curves adjustment. This enables you to have a different effect in highlight areas versus shadow areas of the image, for example. In some cases you might want to lighten the shadows and darken the highlights, while in other cases you might want to darken the shadows and lighten the highlights. And of course with some images you might want to only lighten or darken, though with an emphasis on specific tonal ranges.

So again, it is important to consider the shape of the curve for a Curves adjustment based on how you want to alter the appearance of the specific photo you’re working on.

Today’s Question: What is the reasonable life of a hard drive? In other words, how often should I replace them?

Tim’s Quick Answer: In theory a typical hard drive should operate normally for hundreds of thousands of hours of use. A solid-state drive (SSD) can generally operate for thousands of write cycles, which would generally translate into multiple years (and potentially decades) of reliable use. That said, I do think replacing hard drives every few years is a good idea.

More Detail: There are a wide variety of factors that impact the lifespan of a hard drive or SSD. For traditional hard drives one of the biggest risk factors in my experience tends to be heat, for example. Physical damage, manufacturing defects, and other factors can also play a significant role.

Even if a given hard drive model could be expected to operate normally for one million hours of use, it is also possible that the drive could fail after a single hour of use. This is why a frequent and consistent backup is critically important for protecting your data.

While today’s storage devices tend to be very reliable overall, I do think it can be a good idea to replace your storage about every three to five years. Of course, for many photographers this approach is something that happens somewhat “automatically”, by virtue of filling up a hard drive and needing to replace that drive with a higher capacity drive.

Predicting the failure of a storage device is quite difficult. This is why a good backup strategy is so critical, in conjunction with making sure to keep your storage devices physically safe and protected from extreme conditions.

Today’s Question: Based on your discussion about bit depth, my JPEGs, as shot in the camera, show up as 24 bit depth when looked at in my Windows [operating system] folder. I’m not sure if that information is available on Photoshop or Lightroom, but I am confused by this bit depth. How do I change that number to a 16 bit as you recommend, or change the number in general?

Tim’s Quick Answer: The reference to “24-bit” is actually the same thing as “8-bit per channel”. The operating system is simply describing the total bit depth rather than the per-channel bit depth.

More Detail: Bit depth refers to the total number of potential tonal and color values in an image. In digital photography we generally refer to the per channel bit depth, such as 8-bits per channel or 16-bits per channel.

In other contexts the total number of bits is used instead. This is often the case with film scanners, for example. With an RGB image you have three channels (red, green, and blue). So, if the image is 8-bit per channel there is a total of 24 bits (eight bits multiplied by three channels). For a 16-bit per channel image the total would be 48 bits (sixteen bits multiplied by three channels).

It is worth noting, by the way, that JPEG images can only be in the 8-bit per channel mode. Furthermore, if you have an 8-bit per channel image I don’t recommend converting it to 16-bits per channel. Doing so would double the base file size of the image with no real benefit in terms of image quality or flexibility in optimizing the image.

Today’s Question: In Lightroom > Preferences > Performance, do you recommend enabling “Use Smart Previews Instead of Originals for Image Editing” in order to speed up performance?

Tim’s Quick Answer: Yes, having this option turned on can improve performance in the Develop module in Lightroom, especially if the source images are of a particularly large size in terms of resolution. If you have adequate storage space for the Smart Previews and your photos have a very high resolution, I would recommend turning on this option.

More Detail: The option to use Smart Previews in the Develop module rather than the original source image enables you to potentially streamline your workflow. Put simply, enabling this option can speed up performance when applying adjustments in the Develop module.

My testing has demonstrated that the performance improvement is generally rather modest. The benefit is more pronounced with images that have a very high resolution. In other words, if you’re using a camera that has a 40-megapixel sensor you can expect a more significant benefit compared to images captured with a 20-megapixel sensor. That is because the difference in the amount of data will be more significant with higher resolution captures.

Of course, you also need to consider the amount of additional storage space required for those Smart Previews. You can generally expect to consume around 2MB of hard drive space for each Smart Preview. That isn’t a tremendous amount of space, but it can add up.

It is also possible that the preview in the Develop module based on a Smart Preview won’t be completely accurate, since the original source image is not being taken into account when working exclusively with Smart Previews.

If you are seeing slow performance in the Develop module, with adjustments taking time to be reflected in your preview images, I would most certainly recommend turning on the option to use Smart Previews in order to help improve that performance.

Today’s Question: Do all cameras have approximately the same bit depth or do they differ significantly? If so what is the difference?

Tim’s Quick Answer: Most cameras today provide 14-bit per channel analog to digital conversion. A small number of higher-end cameras offer 16-bit per channel support, and some (mostly older) cameras are limited to 12-bit per channel. Cameras with higher bit depth have the potential for greater detail with smoother gradations.

More Detail: Light represents an analog signal, and so you could say that light could theoretically be divided into an infinite number of brightness values. However, digital images are described with discrete numeric values, and so a limit to how many values are available must be defined.

You can think of this limit as being a limit to how many digits can be used for a number. If you are limited to a two-digit number, the maximum value is 99. For a three-digit number the maximum value would be 999.

In the context of digital images, bit depth defines the limit in terms of how many possible values are available, and therefore how many tonal and color values are possible. Cameras that only offered 12-bit per channel analog-to-digital (A/D) conversion were limited to a total of 4,096 tonal values per channel, or more than 68 billion possible tonal and color values for a full-color image.

Most cameras employ 14-bit per channel A/D conversion, providing 16,384 tonal values per channel, or more than 4 trillion possible tonal and color values overall. And those few cameras that offer 16-bit per channel A/D conversion offer 65,536 tonal values per channel, or over 281 trillion possible tonal and color values.

Of course, you only really need about 8-bit per channel information to provide a photographic image of excellent quality. But having more information can ensure you retain smooth gradations and optimal overall quality, even after strong adjustments are applied. So there is an advantage to higher bit depth, but that advantage has a diminishing return.

When processing your images after the capture, most software only provides support for 8-bit per channel and 16-bit per channel modes. So when your camera “only” offers 14-bit (or 12-bit) A/D conversion, you would still generally be working with that image in the 16-bit per channel mode. You simply don’t have full 16-bit information in that scenario.

I wouldn’t recommend choosing a specific camera based only on the bit depth of the A/D conversion for that camera. Many other factors are far more important both in terms of image quality and overall feature set. All things considered, I would say that most cameras today are about equal in terms of the net effect of their bit depth, in large part because the vast majority of cameras today offer the same 14-bit per channel A/D conversion.

Today’s Question: How important is it really to work at a high bit depth? Will I even be able to see the difference in my photos?

Tim’s Quick Answer: That depends. When a photo requires strong adjustments or will be presented as a monochrome image, working at a high bit depth can be critical. When working with a full-color photo that only requires minor adjustments, the bit depth isn’t likely to be a significant factor. I simply prefer a conservative approach that involves always using 16-bit per channel mode when optimizing photos.

More Detail: The bit depth used when applying adjustments to your images affects the total number of tonal and color values available for the image. That, in turn, determines the degree to which smooth gradations of tone and color can be maintained, even as you apply strong adjustments.

A monochrome (such as black and white) image at a bit depth of 8-bits per channel will only have 256 shades of gray available, while a 16-bit image will have 65,536 shades of gray. That can translate into a tremendous risk of posterization (the loss of smooth gradations) for an 8-bit monochromatic image, even with modest adjustments.

A color image at 8-bits per channel will have more than 16.7 million possible tonal and color values available. At 16-bits per channel that number jumps to over 281 trillion tonal and color values.

While 16.7 million possible tonal and color values is generally adequate for ensuring smooth gradations within the photo, strong adjustments can result in a degree of posterization. It will usually take a very strong adjustment (perhaps combined with an image that had been under-exposed initially) to create visible posterization with a color image, but the point is that there is a degree of risk.

For many photographers the difference may be virtually non-existetnt between an 8-bit per channel and 16-bit per channel image for a color photograph that doesn’t require strong adjustments. However, my personal preference is to always work in the 16-bit per channel mode when possible, just to ensure I am always producing an image with the highest potential quality.

It is important to note, however, that if the original capture does not provide high-bit data, there is no real advantage to converting an 8-bit image to the 16-bit per channel mode. This is one of the key reasons I prefer RAW capture rather than JPEG capture (along with the risk of compression artifacts with JPEG captures).