| .TH IM_LITECOR 3 "5 December 1991" |
| .SH NAME |
| im_litecor \- perform light correction |
| .SH SYNOPSIS |
| .B #include <vips/vips.h> |
| |
| .B int im_litecor(in, white, out, clip, factor) |
| .br |
| .B IMAGE *in, *out; |
| .br |
| .B int clip; |
| .br |
| .B double factor; |
| .SH DESCRIPTION |
| .B im_litecor(3) |
| performs light correction on the image held by the IMAGE descriptor in, |
| with respect to a reference white image held by the IMAGE descriptor white. |
| The result is written onto the IMAGE descriptor out. The function works |
| on byte one channel images only. |
| |
| The flag clip can take two values 0 and 1. If clip is 1 then the input is |
| corrected with reference to the maximum value of white (maxw) as follows. |
| |
| pel_out = factor * pel_in * maxw / pel_white. |
| |
| If clip is 0 then the output is scaled with the maximum possible output set |
| to 255. In this case factor is not used but it must be set to a dummy value. |
| |
| The basic reason for lighting correction is that the input frame does not |
| have a uniform distribution of white light due to the optical response of |
| the lens. The function accepts a white image which is a simple multiple |
| of the input image in size; for example it is possible that the white |
| is a subsampled version of in; however the sizes of in must be an exact |
| multiple of the white. If clip is set to 0, lighting correction is |
| carried out and the result is scaled between 0 and 255. This can be used |
| to correct individual frames. |
| |
| If multiband images are grabbed, then flag should be set to 1, since |
| no scaling must be done. In this case the factor can reduce the number of |
| clipped pels if overshooting occurs in the brightest band. The program |
| prints the number of clipped pels with im_warning(3). |
| .SH RETURN VALUE |
| The function returns 0 on success and -1 on error. |
| .SH BUGS |
| clip==0 case not working too well. |
| .SH SEE\ ALSO |
| im_add(3), im_lintra(3), im_multiply(3). |
| .SH COPYRIGHT |
| .br |
| N. Dessipris |
| .SH AUTHOR |
| N. Dessipris \- 05/12/1991 |
