[Radiance-general] macbethcal error

[Rob Guglielmetti]

Gregory J. Ward wrote:

> Hi Rob,
>
> I suspect that the corners of your image are not specified in the  
> proper coordinates, or are not the right corners -- assuming you used  
> the -p option to macbethcal.  Remember that the y-coordinate from  
> Photosphere is reversed from that produced by ximage, which is what  
> macbethcal expects...
>
> -Greg
>
> P.S.  If you're still stuck, send me your image and I'll see what I  
> can do with it.


Hey Greg, I think I got it.  Thanks.  I think it was cropped too 
closely, is all.  I ended up re-shooting the whole thing (a few times), 
anyway.  I'd send or post a copy of the new debug image, but I'm having 
a problem with my internet connection here at home, and can't send any 
large files at the moment.  =8-/ 

I was getting a lot of patches out of gamut with my northern light 
images, so I did it again under direct sun, and only had two patches 
with the diagonal lines on them which I guess is good. (?)  The 
greyscale sequence at the bottom row was perfect, but the colors were 
less so.  Maybe this is a white balance issue?  I fixed it at 
"sunlight", but I'd like to do some more tests when I have sun at my 
disposal again. 

Interestingly, I got some variation on some paint color swatches that 
were photographed twice with two different backgrounds.  I have two 
different materials (sofa cushions) that I wanted to sample, onto which 
I taped three paint color swatches that I also wanted to sample.  I 
photographed each cushion with the same three swatches taped on, ran 
them through pomb with my .cal file generated with macbethcal, but the 
rgb values (plucked from ximage) for the three swatches differ somewhat:

sample1
======
greenish background: .56 .52 .38
brownesque background: .58 .55 .41

sample2
======
greenish background: .35 .30 .22
brownesque background: .47 .41 .29

sample3
======
greenish background: .41 .35 .25
brownesque background: .38 .32 .24

sample2 shows the most variation, but truthfully I'm not sure what's an 
acceptable range here.  sample1 and sample3 have very similar rgb values 
in both images, which gives me a warm fuzzy feeling about the whole 
process.  But sample2 seems pretty variate.  Is this as good as I should 
hope for, or is my technique off here?  These samples were photographed 
within seconds of each other, under direct (Colorado!) sun, so I think 
the lighting is pretty consistent. 

- Rob Guglielmetti