Ask Tim Grey

Today’s Question: On several occasions you have provided guidance on specific uses for blend modes in Photoshop. But could you explain exactly what a blend mode is to being with?

Tim’s Quick Answer: Blend modes are a feature of Photoshop that enable you to combine two or more layers, with specific math being applied to the pixel values of those layers. The blend modes are divided into categories based on their effect, such as lightening, darkening, and adding contrast.

More Detail: I think a couple of examples could be helpful to better understand how blend modes work in Photoshop. Let’s assume a simple scenario where there are two grayscale (black and white) image layers in a Photoshop document, and the top layer is set to a given blend mode. I’ll also present the details here using luminance values for a grayscale image based on a bit depth of 8 bits per channel. In other words, my numbers will be based on a range from 0 for black to 255 for white.

One of the simpler blend modes is Multiply. As the name implies, with the Multiply blend mode each pixel value in the “top” layer is multiplied with the corresponding pixel in the “bottom” layer. The product of that multiplication is then divided by 256 to determine the final value. So, for example, a pixel value of 81 on the top layer and 128 on the bottom layer would produce a product of 10,368, which divided by 256 gives a final result of 41. As a result of this math, using the Multiply blend mode will always result in a darker pixel value, except in the case of white and black, which would remain unchanged.

The Screen blend mode is essentially the opposite of the Multiply blend mode in terms of the net effect. The math involves multiplying the inverse value for each pixel. That means subtracting each value from 256 to produce the inverse values, multiplying the result, dividing by 256, and inverting again (subtracting from 256). So, with the same values as above (81 and 128), the inverse values would be 175 and 128. The product of those would be 22,400, which divided by 256 yields 87.5. Subtracting that value from 256 produces a final result of 168 (based on the closest whole number. The result is that pixel values will become brighter when the Screen blend mode is applied.

Of course, as a photographer working in Photoshop there is generally not much benefit to understanding the math behind each of the blend modes. My point in sharing this info was more to demonstrate that blend modes are relatively simple in concept, applying math equations between pixel values on two (or more) layers. In some cases that math can certainly get quite complicated, so I think in general it is more helpful to understand the basic concepts behind the blend modes.

The first set of blend modes includes the “normal” blend modes. Then come the darkening blend modes, the lightening blend modes, the contrast blend modes, the inversion and cancelation blend modes, and the color component blend modes.

For a little more info on blend modes, you might be interested in the article “6 Favorite Blend Modes” from the March 2013 issue of Pixology magazine.

Today’s Question: Can you help me better understand when I should be using virtual copies in Lightroom? Should I make a virtual copy every time I am going to apply adjustments to an original photo?

Tim’s Quick Answer: Generally speaking, I would say that Virtual Copies in Lightroom should be used when you want a second interpretation of a photo. For most photographers I would say there is no benefit to creating a virtual copy for every photo you optimize in the Develop module.

More Detail: A Virtual Copy simply represents a second set of adjustment settings for a photo. When you apply adjustments to a photo in the Develop module within Lightroom, you aren’t actually altering the original capture. Instead, the specific adjustment settings for the image are stored in the Lightroom catalog (and possibly in metadata for the image file itself). Those adjustment settings are reflected in the preview of the image you see in Lightroom, and are applied to any derivative image you create by exporting or otherwise sharing a photo.

But again, a Virtual Copy simply represents an additional set of adjustment settings for an image. As a very basic example, you might have one set of adjustments for a color interpretation of the original image, and then a second set of adjustments (in the form of a Virtual Copy) to produce a black and white interpretation of the photo.

When you create a Virtual Copy, it will appear that you have a second copy of your photo in Lightroom. But in fact you simply have a second version of the original source image. That also means you aren’t doubling the amount of storage space required for the image when you create a Virtual Copy, because the only thing you’re actually duplicating is the information about the adjustments being applied to the image.

Some photographers do prefer to create a Virtual Copy in Lightroom every time they start working on one of their images. This provides an easy way to clearly see the difference between the original image without any adjustments beyond the default settings in Lightroom, and the final version of the photo you’ve created through various adjustments in the Develop module.

Personally, I don’t like the notion of creating a Virtual Copy for every image I will work on in the Develop module in Lightroom. I prefer to only create a Virtual Copy when I want to produce an additional interpretation of the image. That could mean I am just experimenting with some refinements to my adjustment, that I’m creating a version of the image that is cropped to a different aspect ratio, that I’m producing a more creative version of an image, or any of a number of other possibilities.

So, I recommend only creating a Virtual Copy when you want a different interpretation of a photo you’ve already optimized, but as noted above some photographers do prefer to use a Virtual Copy every time they work on an image in the Develop module.

Today’s Question: How do I increase the size of the thumbnails in the filmstrip in the Lightroom Develop module?

Tim’s Quick Answer: You can resize the thumbnails on the Filmstrip panel by resizing that panel. When you drag the top edge of the Filmstrip panel up or down, the thumbnails will resize accordingly.

More Detail: When you use the Grid view in the Library module, there is a “Thumbnails” slider on the toolbar below the image preview area. You can drag that slider to the right to increase the size of thumbnails, or to the left to decrease the size of thumbnails. However, that control only affects the size of the thumbnails within the Grid view display.

With the Filmstrip, there isn’t an actual control for changing the thumbnail size, which might lead you to assume that the thumbnails on the Filmstrip can’t be resized. But you can indeed resize those thumbnails by resizing the Filmstrip panel itself.

To resize the Filmstrip you need to position your mouse over the top edge of the panel. The top edge of the Filmstrip is actually the top edge of the black area above the thumbnail display area, not the top edge of the thumbnails themselves. If you position your mouse pointer at the top of the black bar above the row of thumbnails on the Filmstrip, and directly below the toolbar, the mouse pointer will change to a resizing icon. This pointer looks like a horizontal bar with arrows going up and down from that bar.

Once you have the mouse pointer hovering over the top edge of the Filmstrip, simply click and drag upward to increase the size of the Filmstrip panel (and thus increase the size of the image thumbnails), and drag downward to reduce the size of the panel and thumbnails.

Today’s Question: In Photoshop is there a straightforward automated way to combine multiple layered images so that each layer has equal value/opacity when combined, to create the equivalent of a multiple exposure? I use a formula to reduce the opacity at each layer (50%, 33%, 25%, etc.) but it is time consuming and repetitive.

Tim’s Quick Answer: A better approach here, both in terms of convenience and a more accurate multiple exposure effect, would be to convert the blend mode for each layer to the Screen blend mode, and then apply overall adjustments as needed to fine-tune tonality.

More Detail: When you combined two layers using the Screen blend mode, you are creating the same effect as a double-exposure effect. In other words, the two exposures are combined to create a brighter image with blended details.

It is very easy to change the blend mode for a series of image layers. The first step is to create a composite image that includes layers for the individual photos you want to combine into a multiple-exposure effect. From Adobe Bridge you can select the photos to combine and then choose Tools > Photoshop > Load Files into Photoshop Layers from the menu. In Lightroom you can select the images and choose Photo > Edit In > Open as Layers in Photoshop.

You don’t need to change the blend mode for the Background image layer to the Screen blend mode, but I prefer to do so anyway because sometimes I like to change the order of the layers. If you want to be able to change the blend mode and layer order for the Background image layer, you’ll need to convert it to a “normal” layer by double-clicking on the thumbnail for the Background image layer on the Layers panel and clicking OK in the New Layer dialog that appears.

You can then select all of the image layers by clicking on the thumbnail for the top-most layer on the Layers panel, then holding the Shift key on the keyboard and clicking on the bottom-most layer on the Layers panel. If you have not converted the Background image layer to a normal layer you can exclude that layer from the selection.

Finally, you can change the blend mode for all of the selected layers. Click on the blend mode popup (it isn’t labeled as such, but the default setting is “Normal”) and choose “Screen” from the popup list. This will create the multiple exposure effect for the selected layers.

To produce a “normal” multiple exposure effect with this approach you would need to capture images that are darker than the correct exposure. The specific exposure compensation required will depend on how many images you plan to combine. If you did not apply such a compensation, the resulting image using the Screen blend mode will be rather bright. You can simply add a Curves adjustment layer at the top of the Layers stack, however, to apply a darkening effect to the overall result. And, of course, if you’d like you can also vary the contribution of each image layer to the overall effect by reducing the Opacity setting for certain layers.

In general, however, you should find that by simply converting all of the image layers to the Screen blend mode and applying an adjustment to darken the overall result, you have a great starting point for a multiple exposure composition.

Today’s Question: I recently attended a workshop that included an impromptu portfolio review. To gather the images for the review, I did an “Export as Catalog” from a Collection that I had created, and then copied the new catalog and the images to an external hard drive to use with my travel laptop. So far, so good. The review went well, and I made some changes to some of the images based on recommendations by the reviewer. Now, I’m home and want to merge the new changes with the previously modified images on my home computer. Since these are not new images, it’s not as simple as merging catalogs, or is it?

Tim’s Quick Answer: The solution here could be a bit challenging, depending on the specific details of what has been done. The task would have been remarkably simpler if you had employed Lightroom Mobile (perhaps even through the Lightroom website interface) for purposes of your portfolio review.

More Detail: This scenario is actually a lot more complicated than it might seem on the surface, in part because you used a collection that presumably contained photos from a variety of different folders. Lightroom does not enable you to simply “synchronize” multiple versions of a catalog in this way, so that you can update metadata or adjustments for photos across multiple catalogs.

In concept, there is a not-too-difficult solution here. First, you could make sure that the “Automatically write changes into XMP” checkbox is enabled on the Metadata tab of the Catalog Settings dialog (found from the Edit menu on Windows or the Lightroom menu on Macintosh) for both of your catalogs. Then copy the XMP files for the images from your portfolio review catalog to the appropriate folder for the source images based on your master catalog. Then use the “Synchronize Folder” command (found by right-clicking on the applicable folder within the master catalog) to synchronize metadata (including adjustments) into your master catalog based on the XMP files on the hard drive.

If all of the photos were in the same folder, this process is not especially difficult. You essentially ensure that XMP files are created for all photos in the applicable folder, copy those XMP files to the “master” folder, and then synchronize the folder to update metadata in the Lightroom catalog. But when photos are spread across multiple folders, this process can obviously be rather complicated.

As noted above, the overall workflow would have been greatly streamlined if you had used Lightroom mobile for this purpose, rather than exporting a new catalog. The collection you created for the portfolio review could have been enabled for synchronization. You could then use Lightroom Mobile on a mobile device (such as an Appl iPad) or through the Lightroom web interface (https://lightroom.adobe.com) to update the adjustment settings for the photo. To be sure, not all adjustments available in Lightroom on the desktop are available for Lightroom mobile, but those adjustments that were updated would have then synchronized automatically back to your master catalog.

Today’s Question: I know that JPEG images degrade if opened and saved repeatedly. What happens to a JPEG when it’s used as a layer in a larger Adobe PSD file that gets opened and edited a lot? Does that layer suffer even if never touched in further editing, or is its quality locked into what it was when it was first added to the PSD file?

Tim’s Quick Answer: When you add a JPEG image as a layer to a Photoshop PSD file, there is no longer any JPEG compression applied to the image data. As a result, you don’t need to worry about the potential for compounded image degradation caused by re-saving an updated image with JPEG compression.

More Detail: The compression used for JPEG images is “lossy”, meaning that some degree of information is lost in the process. In essence, JPEG compression operates by dividing an image into “blocks” of pixels (in many cases these blocks are 16 by 16 pixels in size) and then simplifying the information contained within those blocks. There is the potential for some loss of detail and image quality as part of this process, as well as for artifacts to appear in the image as a side effect of the JPEG compression.

If you open a JPEG image, make changes to that image, and re-save as a JPEG, there is some degree of cumulative quality loss in that updated image file. That is because different pixel values are being processed with the JPEG compression algorithms, producing a new result and with the potential for some lost quality as a side effect.

When you use a JPEG image as the basis of a layer in a Photoshop PSD image file (or TIFF image for that matter), the pixels in that layer are no longer a JPEG image, and will no longer have JPEG compression applied when you save the new “master” document that contains that image layer. Therefore, there won’t be additional quality loss caused by the JPEG compression, since no such compression is being applied.

It is worth noting, by the way, that in most typical workflows the cumulative loss of quality with JPEG compression is mostly a theoretical issue that won’t cause an obvious visible loss of image quality in most cases. I should also add that when you save a TIFF image in Photoshop you do have the option to make use of JPEG compression, which would result in the potential degradation of image quality. But as a general rule I recommend against the use of JPEG compression when saving a TIFF image.

Today’s Question: I followed your advice to make use of my camera’s ability to record to two media cards at the same time when capturing photos and videos, so I have a built-in backup. But when I go to format the cards after downloading, I see that significantly more space has been used on one card compared to the other. What is going on here?

Tim’s Quick Answer: Most digital cameras I’m familiar with that offer two media slots are only able to record video to one card at a time. So while you are able to capture still photos to two cards at a time, it is common for video to be only recorded to one of the cards.

More Detail: I am a big fan of cameras with two card slots that include the option to configure the cards for simultaneous recording. This option enables you to have a real-time backup of your photos. Granted, if you lost your camera you would lose both cards and potentially still be without a backup. But this option does provide insurance against a card failure.

However, as noted above, with most cameras you aren’t able to save video captures to two cards at a time. I assume this is purely a matter of bandwidth constraints, since video files tend to be rather large to begin with and thus require more time (and space) to save compared to still captures.

So, while I capture still photos to two cards at a time with my camera, video captures are only recorded to a single card. And even with this built-in backup, as noted above the backup is still located within your camera. Thus, if your camera were lost you would lose both copies of your photos. In other words, with photo or video captures that are of particular value to me, I am still eager to download the captures to a computer or other storage device as quickly as possible, in order to provide another backup on a separate physical device.

Today’s Question: There are occasions in Lightroom when I would like to erase a portion of a radial filter adjustment that I am attempting. This would allow more detailed shaping to the effect than just tugging on the adjustment points of the standard tool. Is this possible somehow?

Tim’s Quick Answer: You can indeed combine the basic effect of the Adjustment Brush and the Radial (or Graduated) Filter in terms of which areas of the image are affected by a targeted adjustment. Just keep in mind that there are some challenges in terms of your flexibility in refining the definition of the portion of the image being affected.

More Detail: When you use the Radial Filter, the Graduated Filter, or the Adjustment Brush within Lightroom’s Develop module, you’re essentially defining two attributes related to a targeted adjustment. First, you’re defining the area of the image being affected by the targeted adjustment. Second, you’re defining the actual adjustment you want to apply to that area.

Lightroom 6/CC allows you to combine the effect of the Adjustment Brush with either the Graduated Filter and the Radial Filter. The first step is to define the overall shape of your targeted adjustment using either the Graduated Filter or the Radial Filter. You can then use the Brush option at the top of the panel for the Graduated Filter or Radial Filter adjustments to effectively work with the Adjustment Brush while you’re using one of these two filters.

With the Brush option, just like with the Adjustment Brush, you have the option for an “A” brush or a “B” brush, as well as an Erase brush. So you can erase portions of the mask that defines the area being affected by your targeted adjustment, and the “A” or “B” brush to add portions to the mask.

So, for example, if you want to apply an adjustment to the central area of the image using the Radial Filter, but then also apply the same adjustment to additional areas of the photo, you could draw an ellipse with the Radial Filter tool and then use the Erase option for the Brush to paint the adjustment into additional areas of the photo.

The big challenge comes with making changes to an existing Graduated or Radial adjustment after you’ve used the Brush option. If you were to, for example, move the Graduated or Radial shape after performing some painting with the Brush option, the brush strokes will no longer align in the same way with the existing shape you had created.

Based on these limitations, my recommendation is to start with either the Graduated Filter or the Radial Filter, and to get that shape as close to perfect as possible before working with the Brush option. Then fine-tune with the Brush option as needed, and of course refine the overall adjustment effects as well.

Today’s Question: I know you are supposed to be able to set the black and white points for an image in Photoshop using Curves, but the sliders below the histogram have disappeared. Has this feature been removed, or did I do something wrong to cause them to be hidden? Can I get them back?!

Tim’s Quick Answer: It sounds like you have simply activated the “pencil” tool within the Curves adjustment. Simply switch to the “anchor point” mode and the sliders for the black and white point adjustments will appear again.

More Detail: The “pencil” tool for the Curves adjustment can be activated by clicking on the pencil icon, which can be found among the vertical column of icons to the left of the histogram display on the Properties panel. With the pencil tool activated you can draw a free form shape for the Curves adjustment. This can be helpful for fine-tuning your adjustment when the shape of the curve hasn’t gone exactly according to plan.

When you are in the “pencil” mode, you won’t see the sliders for the black and white point (nor actual values for the Input and Output options below the histogram). However, if you switch back to “anchor point” mode, you’ll get those controls back. To return to the anchor point mode, click the button directly above the pencil icon among the vertical column of icons to the left of the histogram on the Properties panel.

As a general rule I prefer to work with the anchor point mode for the Curves adjustment. However, from time to time it can be very helpful to switch to the pencil mode to cleanup the shape of the curve. You can also click the “smooth” button below the pencil icon to smooth out any rough corners you drew on the curve with the pencil tool.

Even after working with the pencil feature, however, I will generally switch back to the anchor point mode to finalize the overall shape of the curve for the Curves adjustment for an image. But perhaps most importantly in the context of today’s question, the black and white point sliders that disappear when you’re working in the pencil mode will return when you return to the anchor point mode for a Curves adjustment.

Today’s Question: I’ve used the Content Aware tool [in Photoshop] ever since it was introduced, but have been unable to locate it since I upgraded from Photoshop CS5. It used to be ganged with the Clone Stamp tool, which is a logical place to find it. Where is it now and why did they hide it?

Tim’s Quick Answer: There actually isn’t a Content Aware tool (although there is a Content-Aware Move tool, as noted below). Rather, there is a technology referred to as “Content Aware” that is available in a variety of places within Photoshop, including the Spot Healing Brush tool, the Fill command, and elsewhere.

More Detail: I don’t recall whether the Spot Healing Brush tool (or any of the other cleanup tools) was ever “bundled” with the Clone Stamp tool on the toolbox. But regardless, the Spot Healing Brush tool is now found on a button two positions above the Clone Stamp tool on the toolbox. You can also use the keyboard shortcut of “J” on the keyboard to activate the Spot Healing Brush tool.

Note that the button for the Spot Healing Brush tool on the toolbox is a “bundle” that also includes the Healing Brush tool, the Patch tool (which also includes the Content Aware feature), the Content-Aware Move tool (which, as the name implies, makes use of the Content Aware feature), and the Red Eye tool. You can click and hold the mouse pointer on the button for the Spot Healing Brush tool to open a flyout menu that includes these additional tools.

You can also find the Content Aware feature as an option for the Fill command. Simply create a selection within the image of the area you want to clean up, and then choose Edit > Fill from the menu. Choose “Content Aware” from the Contents popup in the Fill dialog, and click OK to fill the selection using the Content Aware technology.