Big Ben's Panorama Tutorials

Colour Correction

There are two sources of colour/brightness variation that have to be accounted for with these source images. The first is radial luminance fall off. This can be corrected using the Panorama Tools Correct filter in Photoshop (Filter > Panorama Tools > Correct) or in the Source Images section of PTGui (which is handy for correcting a batch of images). For my fisheye lens I use a value of 7 for all channels.

The second correction is more difficult, but can often be handled quite well by the new colour correction feature of Panorama Tools introduced in version 2.6.  The difference between the images is caused largely by lens flare, resulting in overall differences in colour and luminance. Panorama Tools compares the histograms of the overlapping regions of the images and then modifies the RGB values of one image so that the histograms match as closely as possible.  A reference image is selected on which to correct the other images.  

Image0 in our source images contains the most lens flare, so it is not selected as the reference image. To illustrate the differences in contrast between the image let's produce a panorama using each of the images in turn as a reference image.

Uncorrected Image

Brightness and Colour Correction

p w1000 h500 f2 v360 u20 n"JPEG g0 q100" k0

p w1000 h500 f2 v360 u20 n"JPEG g0 q100" k1

p w1000 h500 f2 v360 u20 n"JPEG g0 q100" k2

The most noticeable improvement is in the centre of the panorama at the seam running down the chimney. More subtle improvements can be found on the walls where the lighter "window" image has been matched to the other images. 

Another notable region of improvement is the outside areas. These appear completely blown out, however when the image is corrected to match one of the images that do not contain any windows or doors (i.e. have less lens flare) some faint highlight detail is expanded.

The contrast of the last panorama is the best so we'll stick with Image2 as the reference image for colour/brightness.