Anyone who has ever used a camera either digital or film has experienced exposure issues of one sort or another, such as over or under exposure. This is one of the most common problems any photographer will go through, and since some moments in life retaking the photo just isn't the option, you shouldn't be stuck with poorly exposed images. One of Fhotoroom's strong points is it's ability to handle exposure issues in many different ways in many different color spaces, whether it be a JPEG, a Digital Camera RAW file or even a High Dynamic Range image. Here we will focus on dealing with JPEG's, Digital Camera RAW files and Tone Mapped HDR files which are usually either 8 or 16bit images.
In Fhotoroom all of the exposure tools have been put together into what we consider a power filter, the Exposure Filter. This is easily accessible by simply selecting the Exposure Filter located under the menu option Modify | Exposure...
Once loaded you will notice that you have 8 controllable options with the first 4 options focused on how the overall exposure is adjusted and the second grouping of 4 control how the distribution of light is handled or what is referred to as the Contrast of the a photo.
Brightness - This option is the most common of Exposure tools and is found in most graphic applications. It simply adjusts the overall brightness of a photo by uniformly adjusting the pixel values in your image.
Reflection - Since many High Dynamic Range photographers use Mirror Balls to produce their images, some data is lost due to reflection. This is cause no surface is 100% reflective and so this option enables photographers to correct this data loss.
Shift - This option shift all the luminosity values equally across the histogram.
Contrast - This option controls how light is distributed across a given range either 8 or 16bit color space. This depends on which type of photo you are work with a RAW or JPEG.
Highlights - Just like Contrast this option controls the distribution of light but only across the Highlight range. Sometimes adjusting the Contrast option will affect parts of the photo you don't want affected, and that this option enables you to set a different contrast correction to just the Highlights without ever affecting the Shadows.
Shadows - Just like Contrast this option controls the distribution of light but only across the Shadows range. Sometimes adjusting the Contrast option will affect parts of the photo you don't want affected, and that this option enables you to set a different contrast correction to just the Shadows without ever affecting the Highlights.
White Point - This option sets all values above it equal to white. The lower the value the brighter the image becomes.
Black Point - This option sets all values below it equal to absolute black. The higher the value the darker the image becomes.
Gamma - This option is the standard way of adjusting contrast in both displays and cameras but in a non linear method. Most Displays have a gamma level of 2.2, but since there are differences between gamma correction from device to device it is important to be able to adjust this option.