Nitro Manual

Note: This manual is incomplete and will evolve over time. I wanted to get something out to people now rather than wait until every section was done.

Overview

Nitro is an advanced photo library manager and editor. It is able to browse and edit images in both the Apple Photo Library and the File System (i.e., Finder folders on Mac and Files.app folders on iPads and iPhones). All edits are non-destructive. That means that the original image is never modified. Instead, edits are stored as metadata along with the image, and the edited image is reconstructed using the original image as needed. Nitro uses (and extends) Apple’s RAW engine to decode RAW images. Apple's RAW engine supports hundreds of RAW camera formats, as well as DNGs and iPhone ProRAW images. However, there are many cameras that Apple does not support fully. For most of those, Nitro adds additional camera support. These include Compressed Fujifilm images, Nikon HE* format, GoPro RAW and many more. This is one of Nitro’s key advantages over other apps that use Apple's RAW engine. Please note: when this manual refers to iOS, it is referring to both iOS (iPhones) and iPadOS (iPads).

Video Tutorials

You can watch video tutorials of Nitro on YouTube at:

macOS Playlist

iPadOS Playlist

iPhone Playlist

Apple Photos and the File System

Nitro can work with both the Apple Photo Library and files stored in the File System (the Files.app on iOS and the Finder on macOS). When using the Photo Library, any changes you make using Nitro will be stored directly into your photo library. If you are using iCloud Photos, those changes will also be synchronized automatically to your other devices by iCloud. You can continue to edit non-destructively on your other devices and return back again if you like. iCloud Photos is not a requirement for using Nitro. When using the File System, edits, ratings, and other metadata are stored in XMP sidecars next to the original files.

Browsing

You can choose whether to browse the file system or the photo library, and switch between them seamlessly. The way you switch depends on the platform. On macOS, you make a window to browse either the photo library or Finder folders. You can make as many windows as you like and the app remembers the window type and position. You make new windows in the File menu.

Files.app and Finder folders

On iOS, there is a special control at the bottom of the screen that switches between Files.app and the Photos. It looks like this:

On macOS, to make a new window, go to the File menu. You can also drag folders into the library area from the Finder. Initially, the File Browser will have no folders in it. Because the app is sandboxed, it does not have any access to your disk unless you grant it. You do that by using the File menu and adding a folder, or by pressing the Plus button at the top of the library list as shown here:

Selecting a folder will show the contents and expanding the outline will show you subfolders. Nitro by default does not show the contents of subfolders. To do that, choose the button to the right of the Edit button at the bottom of the window.

You can remove folders by right-clicking or by swiping to the left and picking Remove. When you do that, you have the option of removing the folder from the app, or actually moving the folder into the Finder’s trash. The contextual menu has other commands as well, including the ability to make new folders.

A word about permissions. Because Nitro stores ratings and edits in XMP sidecars, it requires the ability to make changes to any folder you add to it. Nitro can browse read-only folders but it will not be able rate, flag, or edit images in those folders. If you add a read only folder, Nitro will display an error message if you try to do any of those things, but you can still view your images.

Photo Library Browsing

In Nitro, the Photo Library is separated into sections. The first section has All Photos and Favorites. Changes you make in Nitro are automatically applied to the Photo Library. For example, if you Favorite an image in Nitro, it will appear as a favorite in Photos or any other app that can view the Photo Library.

The next section is a special section created by Nitro itself. Here are rating albums, as well as albums that Nitro maintains for rejected images, flagged images, as well as images you have edited and exported. Because these are regular albums, they also appear in Photos. Just look for the Nitro folder in Photos. There is also a folder for Smart Albums, which will be discussed shortly. The albums in the Nitro section are managed by Nitro itself. As you rate, flag, edit or do other things in the app, Nitro will add and remove images from those albums automatically. You can see any changes to those albums in Photos as well. While you can also manipulate the albums in Photos, please avoid doing that because there is a chance you will confuse Nitro, especially if it’s running at the same time.

After that are Media Types, such as RAW images and videos. Shared Albums follow. You can view items in Shared Albums, but you cannot edit or change them. This is a restriction imposed by Apple. The last section contains albums that you have created.

At the top of the library is a search field. You can use that to quickly filter your library by album name. In the image below, the library is filtered by "raw" which shows all matches including the enclosing folders.

Sorting and Filtering

When you click or tap on a library item on the left, the contents are displayed on the right in a grid. Images have badges to indicate status such as file type, flag, rating, and edit state. At the bottom of the grid is a status bar as shown below.

The first two buttons let you jump to the beginning and end of the grid list. Following that is a "share" button that lets you export images with control over format and destination. Next is the number of items and sort order, along with a "move to trash" button.

You can sort the contents of the grid by choosing the "Sort" button at the top. On iPhones, the Sort command is in the "..." menu in the upper right.

You can also filter images by tapping the Filter button, or by using the Quick Filter. On iPhones, the Filter interface is in the same “…” menu. The Quick Filter lets you quickly set a filter by rating and flag state. Tap the setting again to clear it.

Once a filter has been applied, the status bar will update to show the filter and display a blue filter button. That tells you there is a filter applied. If you tap the blue button, the filter UI appears. You can get the same thing by tapping the Filter button at the top of the screen.

The filter interface contains a large number of possible choices. If there is an X in a filter row, then that means it's applied. You can click the X to remove the filter. On iOS, the "X" appears to the right of the title.

When filtering the file system, the list of filters is slightly different. For example, there is no concept of albums, so that row is absent. However, there are rows for things like Camera Model which can be filtered for when using the file system, but cannot be done efficiently in the Photo Library. Filters are "AND" operations, which means that if you filter by "Movies" and "2 stars", you will get 2 star movies, not "2 star" OR "movies".

There are two ways to filter by file name. One way is by using the filter UI and expanding the File Name section. The other way is to type into the field next to the Quick Filter popup. The one in the Filter UI has more options for filtering by name, such as "contains" or "does not contain", while the one in the Quick Filter is simply a "contains" search. For example, if you type "arw", it will look for any file containing the sequence of characters "arw" anywhere in the name. This filter is case-insensitive. This is a quick way to search file extension ("ARW" is the file extension for Sony RAW images).

Smart Albums in the Photo Library

When using the Photo Library, you can also create a smart album by clicking a button at the bottom of the filtering interface.

When you save a smart album, you can set the name, and it will appear in the Smart Albums folder in the Nitro section on the left. You can see these albums in Photos, but if you look at them, you will notice two things. First, they have funny names and second, they are empty. Because they are smart albums, they only show images in Nitro. Also, please do not change the names of these albums or move them elsewhere in the library. That will cause the Smart Album to stop working. To revise the smart album's query, click on the smart album to display it, and then click the Filter button. Then change the filter settings and click the Save button in the upper right.

Because these are photo library albums, they will synchronize across your devices if you use iCloud Photos, so you can make a smart album on one device and view the smart album on another device running Nitro.

Note: Albums are features of the Photo Library, so none of the Nitro albums for rating, edit, or smart albums appear if you use the file system to manage images. You can still filter by rating, edit and such in the file system, but you cannot save any queries as smart albums. Also, unless you make a smart album, filters are not saved, so if you quit and reopen Nitro, any filters you have applied will be gone.

Rating and Flagging

Nitro uses a five star rating system. Images initially have a rating of zero (or “unrated”). There is also a flag feature which can be used to flag or reject images. Nowadays, people tend to use the reject flag for a quick, initial review to discard obviously bad images. After images have been rejected, there is often a second pass where images are rated. Depending on the platform, you can rate or flag images in multiple ways.

On the Mac and on iPads with keyboards, the flagging keyboard shortcuts are as follows:

Reject	X	(the ‘x’ key)
Flag	\	(the ‘backslash’ key)
Not Flagged	]	(the ‘right bracket’ key)

The Image menu has submenus for Rating and Flag, where you can view the shortcut keys. You can rate images using the number keys from 0 through 5. Those are single keystrokes for ratings. If you want to use the Command key, you can switch that in the app’s Settings panel. Flagging does not have a command key option, since the command key versions would conflict with other standard operations (like Cut, which is Command-X). If you want to change the shortcut keys for rating or flagging, you can do that by going to the Apple menu and picking System Settings. Then pick Keyboard and configure the keyboard shortcuts there. Instructions can be found here

When you are displaying images in the viewer on iPads and Macs, there is a narrow panel on the left with rating and flag controls. They show the current rating and flag status for the selected image and you can click or tap them as well. On iPhones, the rating and flag controls appear underneath the image.

On iPhones and iPads, you can use gestures to rate and flag. To rate, drag your finger up and down on the left half of the image. The flag, drag your finger up and down on the right half of the image.

In addition, there are settings in the app that will automatically advance to the next image when you apply a rating or flag, as shown below.

This approach to rating and flagging works well with the filter options, where you can filter by rating or flag state. For example, after rejecting images, you can filter by Rejected images and then delete those all together. In the Photo Library, you also can view images by rating and flag by using the smart albums in the Nitro section, as described above.

Finder / Files.app Tagging

Nitro on the Mac is able to read and write Finder tags to your files, and it also displays all of the tags that are set up in the Finder. While it’s straightforward for an app to read the tags on a file, it’s not simple to get the list of all tags that are set up on a computer. That’s because Apple does not provide a straightforward way for apps to get that list. Instead, Nitro has to locate and open a hidden file that contains that information (and the file moves to a new location in almost every OS version). To start with tags, go to the Image menu and pick Set Up Tags…. The app will display a dialog and you should pick your Home directory, because that is where Apple has hidden the file with the list of all tags. In many cases, however, this will fail, because the file is still not readable. You may see this error message:

Unfortunately, the only solution at this point is for you to give Nitro temporary disk access using the System Settings app. Here are the steps to do that.

Open the System Settings app
Select Privacy and Security
Locate Nitro in the list
Turn on Full Disk Access
If Nitro is running, click the button to Quit and Reopen the app. Otherwise open Nitro yourself.
Select Image > Set Up Tags… and select your home directory again.

Once it works, you can go back to System Settings and revoke disk access. Nitro will continue to be able to read that file, but won’t have access to anything else. The Set Up Tags… menu item will be replaced with the list of tags and colors on your machine.

Unfortunately, on iOS, the story is worse. That magic hidden list of tags is not available at all on iOS, so while Nitro can read and display tags, it does not have the ability to set them (since it does not have access to the list of all tags). So, you can view tags in Nitro for iOS, but you cannot set them.

XMP File Overview

Nitro stores ratings, edits, and flags in XMP files. XMP is an Adobe-created standard for storing metadata. XMP is a text file format based on XML. There are public areas (called namespaces) that apps can read and write to, which enables sharing of data between apps. There are also private namespaces that apps use to write data that they don’t expect other companies to read or write. Of course, since XMP is just text, other apps could read them, but generally it’s not done.

Here is an example of an XMP file with the namespaces, public and private areas delineated.

<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 5.5.0">
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
      <rdf:Description rdf:about=""

—— NAMESPACES:
            xmlns:xmp="http://ns.adobe.com/xap/1.0/"
            xmlns:nitro="http://com.gentlemencoders/xmp/nitro/1.0/">

—— PUBLIC DATA:
         <xmp:CreatorTool>Nitro</xmp:CreatorTool>
         <xmp:Rating>1</xmp:Rating>
         <xmp:MetadataDate>2024-06-14T10:55:54-07:00</xmp:MetadataDate>

—— PRIVATE DATA:
         <nitro:Flag>1</nitro:Flag>
         <nitro:EditedPixelSize>{5078, 3072}</nitro:EditedPixelSize>
         <nitro:OriginalPixelSize>{7952, 5304}</nitro:OriginalPixelSize>

      </rdf:Description>
   </rdf:RDF>
</x:xmpmeta>

Ratings: Nitro will read and write ratings to the public namespace, which means that ratings you set in Lightroom, or other apps that use XMP, will show up in Nitro (and vice-versa, with some exceptions).

Keywords: Nitro will read keywords from the public area. The current version of Nitro does not write keywords, but when it does it will write them to the same public area. Lightroom also has areas for hierarchical keywords, which Nitro may support in the future.

Flags: There is no public area for flags, so Nitro reads and writes flags to its private namespace.

Edits: There is no public definition of editing parameters, so Nitro also stores its editing information in a private namespace. For brevity, the above XMP file does not show Nitro’s full editing data, but you can open an XMP file to see what that looks like.

XMP File Names and File Extensions

This would seem to be a simple topic, but nothing is ever truly simple. There are two parts to a file name - the name itself and the file extension. There are two ways of storing XMP data: in a sidecar and inside the original file itself. Adobe writes XMP to a sidecar for proprietary RAW images - that is, anything but DNGs. For DNGs, and non-RAW files like TIFFs, JPEGs, etc. Adobe writes the XMP directly to the original file. This is handy because the metadata is carried along with the pixel data, but it’s a bit dangerous because of the non-zero risk of file corruption. It also doesn’t work if the image is locked or read-only, or if it’s a movie or other format that does not store XMP.

In contrast, Nitro always makes a sidecar file. An option to write to the original file is planned for the future. For proprietary RAW files, the sidecar filename is the same as the original with the file extension changed to “.xmp”. So for DSC0012.ARW, the sidecar will be called DSC0012.xmp. Sidecars are always located next to the original files.

However, for other file types, that naming convention is not guaranteed to work because there could be multiple files with the same root file name. The most obvious case is RAW+JPEG, where there is a JPEG original next to the RAW original. Since it’s possible to work with both files independently, if Nitro used the same naming convention, the XMP files would collide. For example, imagine there is a RAW+JPEG pair called DSC1234.NEF and a DSC1234.JPG. Nitro would name the XMP file for both DSC1234.xmp, which would mean changes to the RAW would overwrite the JPEG’s XMP data or vice-versa. To avoid that problem, Nitro adds the suffix to the XMP file name. In this case, the RAW would get DSC1234.xmp, and the JPEG would get DSC1234_jpg.xmp. The same is true of DNG and other formats. The downside is that other apps may be unable to read these files because they are not expecting that file name convention.

XMP File extension: The other half of the name problem is the file extension. The file extension Nitro uses for XMP is always lower case, even if the original file name is all upper case. That is done to work better with case-sensitive file systems and Adobe apps. iPhone and iPads always use a case-sensitive file system, which means that DSC1234.xmp and DSC1234.XMP are different files. The Mac usually is case-insensitive, so those two names would be the same file on a Mac (unless you deliberately make a case-sensitive file system in Disk Utility). Windows is also case-insensitive.

Adobe apps always use a lower case file extension, so to avoid issues reading and writing data with Adobe apps, Nitro uses the same convention. If it did not do that, then on iOS, you could easily have two XMP files that only differ in the case of their file extensions. However, this is not a perfect solution because not all apps use a lower case extension. Some use uppercase file extensions, and some web services will change the file extension of an XMP file from uppercase to lowercase and vice-versa. It’s something to be aware of on any case-insensitive file system.

The important things to know are 1) the XMP file must have a lower case extension for Nitro to read it and if you somehow get an XMP file that is upper case, you will need to rename it to lowercase, which is covered in the next section.

Reconnect Sidecars: There is a menu item in Nitro for Mac and iOS which lets you rename sidecar file extensions. It’s called Reconnect Sidecars. The easiest way to get to it is by bringing up the contextual menu in the sidebar as shown here.

If you pick it, the app will look for all the sidecars and rename them to have a lower-case extension. This is a rarely used feature, but if you find that the app is unexpectedly not processing your sidecars, check the file extension and use this feature to fix them.

Cross-Machine Workflows: Editing and Rating

As mentioned earlier, Nitro writes edits to XMP files that reside next to the original files.This way, if you need to copy or move the files, the sidecar is easy to include in the operation.

What happens if you make rating or editing changes on an external disk and then move it to another computer? What if you edit or rate images stored on a file server or NAS (Network-Attached Storage)? The short answer is that all the data will appear and be usable on the other machine. There are a few details that are worth discussing, though.

Here are some steps you can try: Using an external hard disk or file server, add a folder to Nitro on device 1 Apply a rating and edit the image (with a preset or whatever you like) If you are in Edit, exit from that mode. If you are using an external disk, then eject the disk. Go to Device 2 and add the same folder. You will see the rating and the edit badge appear (it may take a while depending on the speed of the connection and the size of the folder). The thumbnail and preview, however, will not be correct. That’s because Nitro does not store the thumbnail or preview JPEG in the XMP file (per convention).

To update the thumbnail, do one of the following: On Macs, select the images that need updated thumbnails. Then in the Image menu (or the contextual menu), select Build Thumbnails. On iOS, use the Select button first and then tap the Batch button. Pick Build Thumbnails. Or, go into Edit for these images - Nitro will build the thumbnail when it loads the original image and the editing information from the XMP file.

If you eject an external drive and open Nitro, then it will alert you about directories that are missing. It is safe to select Remove from App. You will not lose any data.

This may happen more frequently on iOS because Apple changes the path to the disk each time it is ejected and reconnected.

One Up (The Viewer)

From the grid, you can tap (iOS) or double-click (Mac) to enter the Viewer. When in Viewer mode, the grid is replaced by a filmstrip and there is a large set of controls on the left and right sides of a large image view, as shown below:

In this view, you can easily view and change ratings or flags. You can also view metadata and enter other modes like Edit, N-Up, and Compare. These modes are described below.

Zoom

Nitro has a number of ways to zoom into images. The first way is by using the controls to the left of the image. Those will increase or decrease the zoom level, or jump between 100% and zoom to fit. You can also pinch (on a trackpad or iOS screen). When using a keyboard, then you can use the following shortcuts:

Zoom to Fit	Cmd-Shift-minus
Zoom to Actual Size (100%)	Z
Zoom In	Cmd-plus
Zoom Out	Cmd-minus

The Editing Panel

Enter edit by picking the first button on the right side panel (see above image).

At the top is shot information including shutter speed ISO and camera. You can collapse it or expand it to get more information. Next is the histogram which includes clipping indicators, which are discussed below. Histograms visually describe the distribution of color or tone in an image; the leftmost column represents black and the rightmost column represents white. The height of the histogram tells you how much of the image (relatively) contains that pixel value. You can also hide the histogram if you like, which both gives more screen real estate, and also improves performance some, because the histogram won't be updated when it's closed.

The next section shows the main editing panels. The first has quick fixes like Auto Enhance, Spot Removal, and Clone. There are some additional ones that will appear based on the image you have. For example, the Highlight Recovery Quick Fix will appear for certain types of RAW images. The next panel contains presets and LUTs. The third has sliders which is the primary topic for this section. The last is masking, which will be covered in a later section.

Undo, Redo, and Show Original

Editing in Nitro is undoable and non-destructive. At the bottom of the right side toolbar are the undo and redo controls. At the bottom of the editing panel is another bar with four controls: Copy Adjustments, Paste Adjustments, Show Original, and Reset Adjustments.

It's best to turn off the clipping overlay when using Show Original to make it easier to see what has changed. The histogram also will update when you use Show Original.

Copy Adjustments will display a dialog that lets you choose which adjustments to copy. Paste Adjustments works the same way, so you can decide what to paste. Reset Adjustments will remove all the adjustments that have been applied. However, if the image has been edited in the Photo Library by another app, the Reset will only remove the Nitro adjustments. To fully revert the image, leave Edit and use Revert to Original.

Reordering Adjustments

The adjustments are listed in a common workflow order. For example, many people crop early in the process to make sure that they are only concerning themselves with the part of the image they're interested in. However, other people like to crop at the end, or perhaps they apply white balance correction first. Nitro lets you reorder the adjustments in the UI. To do that, go to Settings and pick Configure.

You can drag adjustments up and down. You can also change the auto-collapse adjustment setting. If it's on, then adjustment sections will open and close automatically as you use them to save space. Note that reordering adjustments only changes the appearance in the UI; it does not change the order that the adjustments are processed to make an image.

Crop

Let's start with Crop. For most adjustments, you do not need to click the checkbox before working. The checkbox will automatically enable as soon as you start dragging sliders or otherwise working with the adjustment. A reset button will appear as well. You can click the checkbox to turn the adjustment off, or you can clear the adjustment by clicking the reset button.

The controls below the crop checkbox are tools. From left to right:

Crop tool
Straighten tool
Rotate left
Rotate right
Flip vertical
Flip horizontal

The crop tool is mostly self-explanatory; however, an important control appears when you turn it on. In the image below, you can see a number sign button. This controls a rule of thirds guide. Next to it is a megapixel reading that tells you the size of the image after the crop has been applied. Press the "checkmark" button to exit the crop tool.

You can straighten in a few different ways. First, you can drag the straighten slider, which will display a grid as you do that. Second, you can use the straighten tool. When you engage this tool, you can simply drag on a line in the image that should be level, but isn’t (either a vertical or horizontal line - it doesn’t matter). You may find it is easier to drag just above or to the side of the line in question. That will compute the angle and straighten the image.

Slider Basics

Editing sliders in Nitro have a number of additional features to make it easier to set values.

Reset: Double-click the slider to reset the value (you can also double-click the title of the slider)
Precision Mode: Drag the slider vertically about 1 inch (2.5 cm) until the slider ball turns green. Then drag horizontally as then the values will update more slowly.
Nudge (Mac only): you can click the arrows next to the slider value to nudge the values up or down. Hold the option key while clicking to move them a smaller amount.
Manual Entry:
- Mac: click on the numeric field to type in a new value
- iPad and iPhone: tap on the numeric field to get an onscreen mini-keyboard to enter numbers (see below image).

White Balance

The white balance adjustment shows the color temperature and tint of the image, and you can adjust them if the image has a tint you want to neutralize (or add). Color temperature is expressed in degrees Kelvin, where lower temperatures result in a bluer image and higher temperatures in a redder image.

There are also presets for common scenes, such as daylight or fluorescent lighting. One way to adjust white balance is to use the auto white balance control. It looks for an area that it thinks should be a gray value and then changes the temperature and tint so that it matches. Alternatively, you can use an eyedropper. When you use the eyedropper, do something similar to what the auto white balance is doing: look for an area that should be gray. You don't want to choose a white pixel or a very bright one; you don't want something too close to black. Look for a uniform midtone - a patch of color that should be gray, but isn’t -- that gives the white balance algorithm the most latitude. You can also drag the eyedropper to get a white balance change in real-time.

Tone

Next is the Tone adjustment. The tone adjustment is important for controlling brightness in the image. Tone has a large number of sliders.

The first slider is Boost. By default, RAW images can look very flat and lack contrast or “punch.” Boost provides that contrast and punch. Boost is also very important for recovering highlights, and it’s not present in apps from other companies. It controls a key part of Apple's RAW decoder and without control over Boost, highlight recovery is substandard. Boost controls the “look” of the image. The “look” is the mix of contrast, saturation and other sweetening that is applied to a RAW image by default to make it look more appealing. However, in its attempt to make the image look nice, the Boost slider also interferes with highlight recovery, fighting with your attempts to bring down blown-out highlights. You can move the slider yourself, but in Nitro, there's a better way to deal with this problem: use the Recover Highlights Quick Fix (described in detail below). That'll move the Boost slider and other important sliders for you. Note: Boost does not appear for ProRAW images, or non-RAWs like JPEGs and HEIF images, as those file formats to not have the image data necessary to recover highlights. Also, if you want the most control over your RAW images, decrease Boost to 0.5 or shut it off entirely by setting it to 0.0. But if you do that, you will need to do more editing of the image on your own in Nitro.

Exposure is a simple slider for adjusting the entire image's brightness. Setting the value to 1.0 makes every pixel twice as bright. At 2.0, every pixel is four times as bright. Moving the slider to -1.0 makes every pixel half as bright. Highlights just work on the brighter pixels, and shadows are for the darker areas. Midtones are right in the center.

Blacks, Whites, and Boost Shadows are only available for raw images because they control special settings in Apple's decoder. Boost Shadows adjusts the bottom or “black” end of the RAW boost curve, allowing you to manipulate the darker parts of the image. The Blacks slider, in particular, is key for dealing with extremely underexposed areas. It sets the "black point" of the image, which is the value below which all pixels are black (that is, 0.0). Pixels that are black are not affected by Exposure, so if you have a very dark image, you may want to move the Blacks slider in order to "lift" some of the pixels above 0.0, where exposure and other sliders can affect them. The Whites slider works primarily with the brighter parts of the image by modifying the baseline exposure of an image.

Recovery: this slider works like a “selective exposure”. Only the brightest pixels are affected, but unlike highlights, it adjusts the brightness just like exposure. Sometimes you will get better results with Recovery and other times Highlights will work better (or a combination).

Clipping Indicators

As mentioned above, the histogram includes clipping indicator circles at the top. These circles at the top of the histogram clipping indicators are used to identify very bright and very dark parts of the image.

If an image has extremely bright pixels, the circles will light up. If you click on the circles, you get an overlay that shows which pixels are too bright or too dark. Another term for this is clipping because the pixel value is too large to be represented on screen and therefore is clipped to the maximum value of white or black. In other words, the pixel is brighter than the brightest value that can be shown on screen. The first circle is the one you will use most often. It'll show you any pixels that are clipped because they're too bright or are black. In this case, a pixel is considered clipped if any of the components (red, green, or blue) are above 1.0, which is the highest value that is normally seen on a screen. Another word for a clipped pixel is a hot pixel, and a black pixel is sometimes called a cold pixel. If you click on the first circle, you see red for pixels that are too bright and blue for pixels that are black. This is also called a hot and cold pixel overlay. An example appears below.

The other circles are channel-specific clipping indicators, so you can see clipping in just the red, green, or blue channels. There are two histogram-specific preferences. One lets you control how clipping is calculated (all channels or any channel). You can also choose whether histograms are computed in the sRGB or the Display P3 color space. See the Settings interface.

Quick Fix: Highlight Recovery

If you have a true RAW image, the Recover Highlights Quick Fix will appear. It does not appear for ProRAW files, because ProRAW is not truly a RAW image - highlight recovery is not really valid, because the images have already been balanced.

For the best results, start by turning on the first clipping overlay in the histogram. Then drag the first slider (Highlights) and watch the clipping overlay. As you recover highlights, the overlay will shrink in size and detail will appear in the overexposed areas. If you look at the histogram, it will also shift, and data from the right edge will start to shift to the left, which is an indication that detail is being restored. You can then bring up the midtones by moving the second slider, which will brighten the image some. While it’s fine to remove every last clipped pixel, it’s often not necessary, or even preferable. It can be appealing to have some bright areas in an image, especially if there is no detail in those areas anyway. Otherwise, you can lose some contrast and end up with gray instead of white. In other words, it’s possible to overdo highlight recovery. If you want to see the image before and after, you can click the button that looks like two overlapping squares. That is the Nitro icon for Show Original (or Show Unedited Image). Press "Done" to leave the recover highlights tool. You don’t have to use the Recover Highlights to accomplish this task - it is moving four different sliders in the Tone Adjustment: Boost, Highlights, Midtones, and Recovery, but it's a lot easier and it moves the sliders very precisely.

Enhance

The Enhance adjustment contains basic tools like contrast, saturation, and vibrancy.

Vibrancy is like saturation, but it doesn't affect skin tones or orange hues. Deepen and Lighten are smarter versions of Highlights and Shadows. This pair of sliders is similar to Highlights and Shadows but produce better results in general. Deepen operates on the brighter parts of the image, while Lighten operates on the darker parts of the image. The sliders are better than Highlights and Shadows because they do not affect overall image contrast.

Detail

Detail has two basic types of sliders: one for sharpening and one for noise reduction.

Clarity and Sharpen are two types of sharpening sliders. It's best to look at the detail sliders when zoomed in. You can move Sharpen to the left to blur an image. Clarity provides a sharpening effect using a technique called Local Contrast. It is similar, but not identical to the Definition slider found in Photos for Mac and Aperture.

The noise reduction sliders only appear for RAW images. They can be used to increase or decrease the amount of default noise reduction on an image. The Luminance Noise slider affects black and white noise, while the Color Noise controls noise that looks like colored speckles. Sometimes applying strong noise reduction can cause the image to look flat or “plasticky.” If that happens, consider increasing the value of the Detail slider. It restores some “grain” to the image to make it look more natural.

Perspective

Perspective corrects images that are shot off-angle, typically off to the side or up from ground level. The filter works by rotating the image three-dimensionally so that the image data looks like it was shot at the proper angle. By default, the perspective adjustment will attempt to fill the image frame, but that may not be desirable in some situation because it can cut off important parts of the image. In that event, use the Zoom Factor slider to expose the full image without cropping. Once you have done that, you can manually crop the image as you like. When you drag the Vertical or Horizontal sliders, a grid appears to make it easier to line up the image to make it straight. Be careful not to over rotate the image — if you do, the image may become warped.

Instead of the sliders, you can select four corners in the image and Nitro will warp the image so that those become the four outermost points on the image. Perspective automatically crops the image. You can decrease that crop by moving the zoom slider, but if you move it too far, you'll get some black areas. You can use the crop tool to remove them.

RAW Tuning

The RAW Tuning adjustment is at the heart of Nitro, providing unique control over Apple’s RAW Engine. All of the sliders are GPU accelerated and real-time, so adjustments appear as soon as you move a slider. There are a few older cameras that don’t have access to all of the below controls, but most do. Note: The RAW Processing adjustment only appears if you are adjusting a RAW image.

Moiré: This slider reduces the effect of moiré. Moiré is an artifact of digital sensors which can cause colored stripes to appear in finely detailed areas. Cameras with an anti-aliasing filter tend to have less moiré, but they also sometimes capture less detail as a result.

RAW Sharpen and RAW Contrast: RAW Sharpen is a subtle form of capture sharpening which works at the Bayer mosaic level. RAW Contrast is a type of local contrast (which can look like sharpening). RAW Contrast generally has a lot stronger effect than RAW Sharpen. Both are image-dependent — the characteristics of the image greatly affect how these sliders operate and affect the default values of those sliders. Sony cameras, in particular, are mostly unaffected by the RAW Sharpen slider.

Gamut Mapping: In its final processing step, Apple’s RAW engine ensures colors do not exceed the range of the working color space (Adobe RGB or P3). This is called Gamut Mapping. Colors that are near or outside the limit of that color space are changed to fit within the gamut. Without gamut mapping, colors that exceed the limit of the gamut will be clipped. Gamut Mapping usually provides good results but having control over gamut mapping is helpful in some situations. For example, sometimes you may want the colors to be clipped rather than mapped because you prefer the appearance. Or, you may want to use other filters in Nitro to bring the colors back into gamut.

Topics Coming Soon

Metadata and ExifTool

ExifTool

Quick Fixes

Presets

More Adjustments

Masking

External Editing (Mac)

RAW+JPEG Editing (Photos)

Editing on iPhone

Batch Processing

Export

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