By Skip on Tue, 07/23/2013
Difficult Exposure Conditions
- ProCamera (my preferred camera replacement app) ($4.99)
- Adobe Photoshop Express (free)
- Pro HDR ($1.99)
1) Manually Set Exposure Level, Independently of the Scene You're Capturing
Sometimes the vast majority of the image we want to capture is unimportant, yet it overwhelms the subject. It may be that 90 percent of the image is extremely light or extremely dark and our iPhone app cannot therefore fix on a large enough portion of the subject to expose correctly. This still life scene of flower seed heads placed in front of a frosted window is a good example. The challenge when exposing for this scene is that the flower is too small to allow the app to set the correct exposure level. The solution is to find an area with slightly lower light and lock the exposure level before returning to capture the image.
- Image One: No exposure or focus point set.
- Image Two: Screen tapped to generate exposure (circle) and focus (square) points. These points dragged as appropriate. Subject very slightly lighter but not to the required level.
- Image Three: Subject ignored completely and iPhone moved to a darker area. Exposure point moved and ISO/shutter speed monitored. Once padlock appears in the circle the exposure is locked and the iPhone can be moved.
- Image Four: Note ISO/shutter speed are as previously set. As a result the image is exposed as I would like for the processing I propose.
2) High Dynamic Range (HDR) Scene: Fake the HDR Process via iPhone Apps from a Single Capture
The trick here is to expose for the lighter areas so that other areas are underexposed (dark). This is especially useful for landscape shots where the lighter areas may be water or sky. Land areas and other detail can become silhouetted. In this example, what most interested me was the reflection of the sky in the river. I exposed for the reflection and in doing so lost the detail of the surrounding river banks. However, I did not have to deal with any overexposed blown out areas where detail would have been lost. Experience has taught me that you can pull detail very effectively out of dark areas.
- Image One: Since the reflection of the sky was the main interest, using ProCamera, I captured the shot with the exposure point set in the river.
- Image Two: I imported Image One into Adobe Photoshop Express and boosted the exposure three times. This pulled the detail out of the underexposed landscape but resulted in a blown out (overexposed) sky and river. The level of detail hidden and recoverable from the image file by adopting this process never ceases to amaze me.
- Image Three: I imported images one and two into Pro HDR, which combines both exposures and generates a landscape much more aligned with that seen by the human eye.
At this point, I regard this as my base image, and from here, I can go on to process and edit as I see fit. With a bit of artistic license and after using several other apps, I ended up with the image at the head of this article.
3) Use a Specialist HDR App to Capture an HDR Scene
You can use Pro HDR and no doubt a variety of other HDR apps to capture the scene. The following images compare a scene with a High Dynamic Range of light captured using a traditional camera replacement app (ProCamera) and a High Dynamic Range camera app (Pro HDR).
- Image One: Captured with ProCamera with the exposure point set indoors results in a blown out exterior.
- Image Two: Captured with ProCamera with the exposure point set outdoors results in an under-exposed interior.
- Image Three: Captured with Pro HDR results in an image more in keeping with the reality seen by the human eye.
Pro HDR works by first analyzing the scene and then taking two captures in quick succession and combining them intelligently to create a single image. Ideally both my hand and the scene need to be quite static, although the app is intelligent enough to allow for some movement when aligning the two captures.
If I'm in an artistic frame of mind, I can obtain interesting results in busy areas (not unlike the double exposure capability of Hipstamatic, but in a more automated way). Here is an example of a surreal street image captured in Pro HDR. You could edit it in other apps to create an interesting composition.
If any of these pointers on exposure helps you to rescue an image you've created, I'd really enjoy seeing any results you'd like to share.