The built-in camera app on the HTC One X stands out not only for the sheer number of image filters available, but also for the high degree of user customization that is permitted. These filter combinations, dubbed 'Effects' by HTC, can be grouped into two broad categories: those you can apply before taking a shot and those that are used to process post-capture variants of the original image.

The One X has 15 separate Effects filters that can be applied before you shoot an image. You access them by tapping the blue Effects icon next to the shutter button.

The pre-capture Effects are underwhelming to be honest, largely comprising updated versions of effects that have existed in HTC phones at least as far back as 2010. Even more crucially though, these Effects cannot be undone once you press the shutter button. Unlike Instagram, which saves your unaltered original alongside the processed version, choosing a pre-capture Effect on the One X means you're stuck with your choice forever. So if you want to 'un-fisheye' that photo of your dog at a later date, you're out of luck. 

The Effects available after you're taken the picture (demonstrated below) are far more useful. Not least because of the flexibility they provide.

These Effects are simply pre-built combinations of individual filter settings. And you can access and modify these filters directly to create and save your own customized presets.

In the Gallery app, simply tap the image to reveal the Edit menu and choose the Effects option.

 You can begin with a favorite stock Effect and modify its individual filters or start from scratch.

With an Effect selected, tap the Edit button in the upper right.
A list of the filters that make up the Effect are displayed in a column on the left.
You can adjust sliders for an existing filter and/or add any of the app's additional filters.
You also have the option to add a frame around your image.

You can stack as many filters as you like to create a customized Effect preset which is saved alongside the built-in ones, making it easy to apply to additional images. The filter adjustments are surprisingly robust, if a bit fiddly to manipulate due to the tiny slider. If you've got the time to spare though, you can certainly produce results more pleasing than those of the stock Effects.

Face detection and Auto smile capture

The One X offers a face detection feature, accessible from the Camera options sub-menu, in which the camera prioritizes faces when setting focus and exposure. In addition, you have the option of enabling Auto smile capture. When active, the camera will shoot an image automatically when your subject smiles. All you have to do is hold the camera (or place it on a support for a self-portrait).

Face detection and Auto smile capture can be enabled in the Camera options sub-menu of the Settings menu.
With both features enabled, a white box indicates the camera has detected a face and the camera will take a picture as soon as the subject smiles.

While you may well want to leave face detection on for a day of shooting, the prospect of your camera  taking pictures on its own without your consent is obviously less welcome. HTC's method of handling this is at best, confusing. When you switch apps, Auto smile capture is disabled when you return to the camera app, which is sensible enough, although it means the common act of reviewing your image (via the Gallery app) forces you to turn the feature back on again. Yet if you put the phone to sleep via the Power button while still in the camera app, Auto smile capture will be on the next time you wake your phone and could potentially take a picture without you or your subject's knowledge. We'd much prefer that this feature be disabled any time the phone goes to sleep.

Digital zoom

While the One X has a fixed focal length 28mm equivalent lens, the camera does offer a digital zoom. As you can see below, however, image quality deteriorates noticeably when the camera upsamples the image.

The scene as shot with no zoom.
From the same location the maximum zoom setting was used.
100% crop
100% crop

While the zoomed image displays prominent artifacts and edge halos, keep in mind we are viewing the crops here at 100%; something most users will have little cause to do. At smaller, and more typical viewing magnifications these artifacts are less noticeable. So if you'll be sharing lower resolution versions of your images, digital zoom can be a usable, though compromised option.