Hello,
I have a question. I want to get cd/m2 values by using the pvalue. Now
I'm not sure how to get those cd/m2 values - I read somewhere that you
should multiply the values you get from pvalue with 179, but if I do
that I get crazy high values (about 15941203). Do I do something
wrong? I have been trying to search for what pvalue exactly gives you
(I know it's the brightness value but I can't find what unit it is
in), but had no luck on that so far. I also wanted to know if this
value is dependent on the area of your luminance picture or not.
Thank you so much in advance!
Iris
Hello Iris,
If the picture has been re-exposed by some other program (such as pfilt), then there will be an EXPOSURE= line in the header, which you can see with the getinfo command. In any case, you can use the "pvalue -o -b" option to undo this exposure and convert to brightness, then multiply the output by 179 to get luminance in cd/m^2.
This is of course assuming your picture was generated by Radiance in the first place using a properly calibrated scene. If it is just an HDR image you got from somewhere, it is unlikely that the pixels have an absolute basis.
Best,
-Greg
···
From: Iris Moonen <[email protected]>
Subject: [Radiance-general] Brightness to cd/m2?
Date: October 23, 2015 9:19:32 AM PDT
Hello,
I have a question. I want to get cd/m2 values by using the pvalue. Now
I'm not sure how to get those cd/m2 values - I read somewhere that you
should multiply the values you get from pvalue with 179, but if I do
that I get crazy high values (about 15941203). Do I do something
wrong? I have been trying to search for what pvalue exactly gives you
(I know it's the brightness value but I can't find what unit it is
in), but had no luck on that so far. I also wanted to know if this
value is dependent on the area of your luminance picture or not.
Thank you so much in advance!
Iris
Hello,
I've tried that but it doesn't say exposure in the header, and while
using this the values still stay this high. I did notice that when I
change the image size, the values differ. I use "| total" because I
need the average cd/m2 value. Is it possible that I need to divide
this number that I get by pvalue | total before multiplying it with
179?
With kind regards,
Iris
···
2015-10-23 18:31 GMT+02:00 Greg Ward <[email protected]>:
Hello Iris,
If the picture has been re-exposed by some other program (such as pfilt), then there will be an EXPOSURE= line in the header, which you can see with the getinfo command. In any case, you can use the "pvalue -o -b" option to undo this exposure and convert to brightness, then multiply the output by 179 to get luminance in cd/m^2.
This is of course assuming your picture was generated by Radiance in the first place using a properly calibrated scene. If it is just an HDR image you got from somewhere, it is unlikely that the pixels have an absolute basis.
Best,
-Greg
From: Iris Moonen <[email protected]>
Subject: [Radiance-general] Brightness to cd/m2?
Date: October 23, 2015 9:19:32 AM PDT
Hello,
I have a question. I want to get cd/m2 values by using the pvalue. Now
I'm not sure how to get those cd/m2 values - I read somewhere that you
should multiply the values you get from pvalue with 179, but if I do
that I get crazy high values (about 15941203). Do I do something
wrong? I have been trying to search for what pvalue exactly gives you
(I know it's the brightness value but I can't find what unit it is
in), but had no luck on that so far. I also wanted to know if this
value is dependent on the area of your luminance picture or not.
Thank you so much in advance!
Iris
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
Hi Iris,
You really need to share your entire command chain with us. The total program will compute averages, but only with the "-m" option.
Cheers,
-Greg
···
From: Iris Moonen <[email protected]>
Subject: Re: [Radiance-general] Brightness to cd/m2?
Date: October 26, 2015 10:08:32 AM PDT
Hello,
I've tried that but it doesn't say exposure in the header, and while
using this the values still stay this high. I did notice that when I
change the image size, the values differ. I use "| total" because I
need the average cd/m2 value. Is it possible that I need to divide
this number that I get by pvalue | total before multiplying it with
179?
With kind regards,
Iris
2015-10-23 18:31 GMT+02:00 Greg Ward <[email protected]>:
Hello Iris,
If the picture has been re-exposed by some other program (such as pfilt), then there will be an EXPOSURE= line in the header, which you can see with the getinfo command. In any case, you can use the "pvalue -o -b" option to undo this exposure and convert to brightness, then multiply the output by 179 to get luminance in cd/m^2.
This is of course assuming your picture was generated by Radiance in the first place using a properly calibrated scene. If it is just an HDR image you got from somewhere, it is unlikely that the pixels have an absolute basis.
Best,
-Greg
From: Iris Moonen <[email protected]>
Subject: [Radiance-general] Brightness to cd/m2?
Date: October 23, 2015 9:19:32 AM PDT
Hello,
I have a question. I want to get cd/m2 values by using the pvalue. Now
I'm not sure how to get those cd/m2 values - I read somewhere that you
should multiply the values you get from pvalue with 179, but if I do
that I get crazy high values (about 15941203). Do I do something
wrong? I have been trying to search for what pvalue exactly gives you
(I know it's the brightness value but I can't find what unit it is
in), but had no luck on that so far. I also wanted to know if this
value is dependent on the area of your luminance picture or not.
Thank you so much in advance!
Iris
Hello,
Before I used "pvalue -d -b -h -H picture.hdr | total". This gave me
numbers such as 89057. After these mails I've been trying to use
"pvalue -o -b -d -h -H picture.hdr | total -m" but now I get values
which are about 0.2832. The cd/m2 values I should get should be about
700 cd/m2, which I don't get by multiplying either of these 2 values
with 179. What do I do wrong?
With kind regards, Iris
···
2015-10-26 18:21 GMT+01:00 Greg Ward <[email protected]>:
Hi Iris,
You really need to share your entire command chain with us. The total program will compute averages, but only with the "-m" option.
Cheers,
-Greg
From: Iris Moonen <[email protected]>
Subject: Re: [Radiance-general] Brightness to cd/m2?
Date: October 26, 2015 10:08:32 AM PDT
Hello,
I've tried that but it doesn't say exposure in the header, and while
using this the values still stay this high. I did notice that when I
change the image size, the values differ. I use "| total" because I
need the average cd/m2 value. Is it possible that I need to divide
this number that I get by pvalue | total before multiplying it with
179?
With kind regards,
Iris
2015-10-23 18:31 GMT+02:00 Greg Ward <[email protected]>:
Hello Iris,
If the picture has been re-exposed by some other program (such as pfilt), then there will be an EXPOSURE= line in the header, which you can see with the getinfo command. In any case, you can use the "pvalue -o -b" option to undo this exposure and convert to brightness, then multiply the output by 179 to get luminance in cd/m^2.
This is of course assuming your picture was generated by Radiance in the first place using a properly calibrated scene. If it is just an HDR image you got from somewhere, it is unlikely that the pixels have an absolute basis.
Best,
-Greg
From: Iris Moonen <[email protected]>
Subject: [Radiance-general] Brightness to cd/m2?
Date: October 23, 2015 9:19:32 AM PDT
Hello,
I have a question. I want to get cd/m2 values by using the pvalue. Now
I'm not sure how to get those cd/m2 values - I read somewhere that you
should multiply the values you get from pvalue with 179, but if I do
that I get crazy high values (about 15941203). Do I do something
wrong? I have been trying to search for what pvalue exactly gives you
(I know it's the brightness value but I can't find what unit it is
in), but had no luck on that so far. I also wanted to know if this
value is dependent on the area of your luminance picture or not.
Thank you so much in advance!
Iris
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
Hi Iris,
Thanks for sharing your command. The new command should in fact give you the average radiance in watts/m^2, which when multiplied by 179 should tell you the average luminance in cd/m^2 as you desire. If the answer is not what you expect, then something else is going wrong.
-Greg
···
From: Iris Moonen <[email protected]>
Subject: Re: [Radiance-general] Brightness to cd/m2?
Date: October 28, 2015 7:18:23 AM PDT
Hello,
Before I used "pvalue -d -b -h -H picture.hdr | total". This gave me
numbers such as 89057. After these mails I've been trying to use
"pvalue -o -b -d -h -H picture.hdr | total -m" but now I get values
which are about 0.2832. The cd/m2 values I should get should be about
700 cd/m2, which I don't get by multiplying either of these 2 values
with 179. What do I do wrong?
With kind regards, Iris
2015-10-26 18:21 GMT+01:00 Greg Ward <[email protected]>:
Hi Iris,
You really need to share your entire command chain with us. The total program will compute averages, but only with the "-m" option.
Cheers,
-Greg
From: Iris Moonen <[email protected]>
Subject: Re: [Radiance-general] Brightness to cd/m2?
Date: October 26, 2015 10:08:32 AM PDT
Hello,
I've tried that but it doesn't say exposure in the header, and while
using this the values still stay this high. I did notice that when I
change the image size, the values differ. I use "| total" because I
need the average cd/m2 value. Is it possible that I need to divide
this number that I get by pvalue | total before multiplying it with
179?
With kind regards,
Iris
2015-10-23 18:31 GMT+02:00 Greg Ward <[email protected]>:
Hello Iris,
If the picture has been re-exposed by some other program (such as pfilt), then there will be an EXPOSURE= line in the header, which you can see with the getinfo command. In any case, you can use the "pvalue -o -b" option to undo this exposure and convert to brightness, then multiply the output by 179 to get luminance in cd/m^2.
This is of course assuming your picture was generated by Radiance in the first place using a properly calibrated scene. If it is just an HDR image you got from somewhere, it is unlikely that the pixels have an absolute basis.
Best,
-Greg
From: Iris Moonen <[email protected]>
Subject: [Radiance-general] Brightness to cd/m2?
Date: October 23, 2015 9:19:32 AM PDT
Hello,
I have a question. I want to get cd/m2 values by using the pvalue. Now
I'm not sure how to get those cd/m2 values - I read somewhere that you
should multiply the values you get from pvalue with 179, but if I do
that I get crazy high values (about 15941203). Do I do something
wrong? I have been trying to search for what pvalue exactly gives you
(I know it's the brightness value but I can't find what unit it is
in), but had no luck on that so far. I also wanted to know if this
value is dependent on the area of your luminance picture or not.
Thank you so much in advance!
Iris