The PhotoFlow 0.2.5 release

The PhotoFlow image editor is a relative newcomer to the field of free-software photography tools. The project was started in 2014, and some people might consider it an odd choice of undertaking—given that there are, these days, quite a few capable raw-photo editors to choose from. But PhotoFlow does bring something new to the table; it places greater emphasis on the use of layers and masks, akin to the tools commonly found in vector editors, painting applications, and the like. That may make PhotoFlow a more natural fit for users who find an emphasis on raw-image functionality like demosaicing and tone mapping less than helpful.

The newest release of PhotoFlow is version 0.2.5, from December 7. There are source packages available, as well as binaries packaged for Ubuntu and Arch Linux, plus Mac and Windows installers. Those looking to run PhotoFlow on Linux will need to install the VIPS image-processing library; the other dependencies are standard fare for GTK+ applications.

PhotoFlow uses single-window interface; if one opens up multiple images, they are placed in tabs. Within each tab, there is a "Layers" list on the left hand side, an image histogram above the list, a set of zoom buttons in the bottom right corner, and that is about it. At least for now, the UI provides only text labels for the relevant controls. That could make it hard for users to discover that the "+", "G+", and "-" buttons at the bottom of the layer list is where all the fun begins.

To get started, one should click on the "+" button. This pops up an "Add New Layer" window, populated with a slate of layer types, each of which corresponds to some sort of image-adjustment operation. That can feel a little different if you are used to "layer" meaning only a set of visible pixels, but having layers that perform an operation is a concept used in Krita, SVG filters, and in GIMP's filter layers. PhotoFlow offers about 65 layer types at present, grouped by category. "B/C/S/H Adjustment" is a brightness/contrast/saturation/hue layer, "Sharpen" is an image-sharpening layer, and so on. Many include a paragraph of descriptive text in the Add New Layer dialog, and there are some fairly advanced options available, like the foreground-extraction and "inpainting" operations from G'MIC.

So far, this may all sound like standard fare. Where PhotoFlow diverges, though, is in how the various adjustment layers are employed in the user interface. By default, adding a new layer simply inserts it into the layer list (above the currently selected layer or, if no layer is selected, on the top). Double-clicking on the layer's name opens up that layer's block of controls in a new pane on the right-hand side of the window. Inkscape does something similar, but raw photo editors like RawTherapee and darktable insist on packing every adjustment tool's control into a single strip down one side. That strip quickly fills up, requiring the user to scroll up and down with the mouse, hoping not to accidentally click on a slider while trying to get to the tool of interest. After having used PhotoFlow, one also begins to appreciate its lack of "filesystem tree" or "image browser" pane taking up more real estate.

The layer list also allows users to group layers together—new groups are created with the "G+" button. Grouping layers makes it possible to enable and disable multiple layers at once, as well as to rearrange groups of layers on the list. Individual layers can be rearranged, too, but once there are more than a few, dragging and dropping them gets tedious (not to mention error-prone, since getting layers out of order can seriously affect the final image).

PhotoFlow also offers an extensive set of tools for creating and applying masks to an image's adjustment layers. Many layer types include a drop-down filter tool at the bottom of their controls; this option lets the user quickly restrict the adjustment's effect by pixel brightness, saturation, or hue—effectively creating an implicit mask.

The more powerful option, however, is to double-click on the blank rectangle that sits next to a layer's name in the layer list. This will open another tab on the left side of the interface named "opacity (layer name)." In that tab, the user can add mask layers of several varieties. PhotoFlow provides tools for building gradient masks, drawing masks directly onto the image canvas, and several other options. In each case, creating the mask in "opacity (foo)" limits the effects of the operations in the foo layer.

Here again, there are "mask" tools in many other raw-photo editors, but in those other applications the mask-editing features can feel like an afterthought. I am not particularly fond of darktable's approach, for instance, which involves a mask manager widget that is separate from the image-adjustment tools. PhotoFlow binds a mask to each layer or layer group; it is a natural one-to-one mapping and it is difficult to get the masks mixed up.

PhotoFlow has its share of awkwardness, though. For example, a few of the adjustment layers take effect immediately, but those that involve drawing on the canvas—such as the crop tool—do not. The user has to click on a pencil icon in the layer's control panel, which adds an unnecessary step. On top of that, the pencil icon is also present on every other layer control panel, even though it seems to have no function on most of them. Alongside the pencil icon are several other toggle buttons, the purpose of which can be equally unclear for many layer types. The pushpin icon, for example, shows masks in red, but it seems to have no effect on non-mask layers. And there are little peculiarities, such as the fact that there are multiple places on screen where you can enable or disable any given layer (the layer list and the layer's control panel), using different icons.

When one takes PhotoFlow's layer and masking tools together, the result is an editor that is surprisingly easy to use. There is no accounting for taste in UIs, of course, but my suspicion is that many users who have spent time in GIMP, Photoshop, or other general-purpose image editors will have an easier time manipulating effects to achieve the look they want in PhotoFlow than in darktable.

That having been said, a simple and clean interface is easy to implement in the early days of a project, and PhotoFlow is only at version 0.2.5. Perhaps clutter will creep in as the codebase and user community expands; it is hard to say. For now, however, PhotoFlow remains an application to watch. The team is making minor releases every few weeks, each of which bring a handful of new features. There is also a growing set of tutorials (video and text-based) that can help users get up to speed—whether they have experience with other image editors or not.