J
Jusko
Guest
Can anybody tell me please ?
Regards
Jusko
Regards
Jusko
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Phill Brannon
Senior Member
--
Pbase supporter
J
Jusko
Guest
Cantora
Member
I never looked into the concept of a grey card RGB. I figured it'd be neutrul 128 but then I thought why is it called 18%?
I was thinking that it would be 232 if it was 18%
Can some'n explain why?
Dave Woods
BD4U Solutions
I was thinking that it would be 232 if it was 18%
Can some'n explain why?
--
Dave Woods
BD4U Solutions
Steve Bingham
Forum Pro
freelancer54
Leading Member
Hi,
I hope I understand the question correctly....
RGB for 18% black is 209
Based on the chart I have:
0% = 255
10% = 230
20% = 204
30% = 179
40% = 153
50% = 128
60% = 102
70% = 77
80% = 51
90% = 26
100% = 0
I hope I understand the question correctly....
RGB for 18% black is 209
Based on the chart I have:
0% = 255
10% = 230
20% = 204
30% = 179
40% = 153
50% = 128
60% = 102
70% = 77
80% = 51
90% = 26
100% = 0
Mike Warren
Veteran Member
Not sure what you are looking for. If you are trying to print your own 18% Greycard on your home printer, in theory you should start with 222 / 222 / 222. which is the equivalent of C-0 / M-0 / Y-0 / K-18. You will probably get a color cast (depending on the printer and settings), if so adjust from there until neutral...
Mike
---
http://www.pbase.com/mikew714
Cantora
Member
I did the whole 128 grey 18% opacity on a white background and got 232 I thought that made sense 
but by your scale, shouldn't it be 207?
26/10 2.6+204...206.6=207
Dave Woods
BD4U Solutions
I thought that made sense but by your scale, shouldn't it be 207?
26/10 2.6+204...206.6=207
--
Dave Woods
BD4U Solutions
freelancer54
Leading Member
Hi Cantora,
I got "209" by actually making an 18% layer in photoshop in rgb.
It calculates this way, I think:
255/100 = 2.55 x 18 = 45.9
255 - 45.9 = 209.1
I think I'm getting more confused about how to calculate rgb, cmyk, and greyscale. The more I look into this, I find that 18% black in rbg is different than 18% K in greyscale. Geez, that leaves me with more questions!
I got "209" by actually making an 18% layer in photoshop in rgb.
It calculates this way, I think:
255/100 = 2.55 x 18 = 45.9
255 - 45.9 = 209.1
I think I'm getting more confused about how to calculate rgb, cmyk, and greyscale. The more I look into this, I find that 18% black in rbg is different than 18% K in greyscale. Geez, that leaves me with more questions!
If you are trying to make a grey card with your printer, you will need to make sure your printer is well profiled with the paper stock you are using.
Secondly, why would you start with rgb values? Why not start with Lab color mode, and punch in luminance = 50, a = 0, b = 0. An 18% grey card is a card that reflects 18% of the light which reaches the card, and 18% grey = 50% luminance in Lab mode.
If you want to use an RGB colour space with gamma 2.2 the RGB values will be 117. If you use a gamma 1.8 colour space like ProPhoto RGB, the values will be 99.
Some of answered this question over on the Nikon forum.
The problem will come when you print this. If you have not accurately profiled your printer, then don’t bother with it.
--
Geoff B
Just for my own benefit I calculated the RGB values for Adobe RGB and ProPhoto RGB using the gamma formula of
Luminance = C * value to the power of gamma + Black Level, where C=1 and BL =0.
Luminance here is a measure of light energy, and for this question equals 0.18 (or 18%). See http://www.normankoren.com/makingfineprints1A.html
For a gamma 2.2 space –
0.18= (x/255) power 2.2
x= 2.2 root (.18) * 255
x=0.46*255
x=117
For a gamma 1.8 colour space –
0.18= (x/255) power 1.8
x= 1.8 root (.18) * 255
x=0.39*255
x=99
--
Geoff B
Luminance = C * value to the power of gamma + Black Level, where C=1 and BL =0.
Luminance here is a measure of light energy, and for this question equals 0.18 (or 18%). See http://www.normankoren.com/makingfineprints1A.html
For a gamma 2.2 space –
0.18= (x/255) power 2.2
x= 2.2 root (.18) * 255
x=0.46*255
x=117
For a gamma 1.8 colour space –
0.18= (x/255) power 1.8
x= 1.8 root (.18) * 255
x=0.39*255
x=99
--
Geoff B
This is certainly an interesting thread with a wide range of answers none of which are probably right. But in the interest of contribution to the confusion I submit to you the Grey Card from
http://www.kodak.com/US/en/motion/products/tools/card.shtml
If you bring it up in photoshop and use the color picker you will get the values of R 140 G 140 B 132 (or at least that is what I got).
So assuming Kodak knows a thing or two about color, I would say none of us here understands what it takes to make an 18% grey card.
http://www.kodak.com/US/en/motion/products/tools/card.shtml
If you bring it up in photoshop and use the color picker you will get the values of R 140 G 140 B 132 (or at least that is what I got).
So assuming Kodak knows a thing or two about color, I would say none of us here understands what it takes to make an 18% grey card.
I downloaded this card image and opened in PS. The ‘Missing Profile’ warning dialogue box told me that this is an indexed color document in gif format, and doesn’t support embedded color profiles. So what you have down loaded is just a web gif file that has no reference value whatsoever. That is, it shows us a representation of what the Kodak Gray Card Plus looks like, but it is not a reference file.
If you assign an sRGB profile to the gif file to open in PS you get the rgb values that you mentioned. However, they have no value in this discussion.
Both these statements could be true.
) So go look up Norman Koren or Bruce Fraser or someone.--
Geoff B
J
Jusko
Guest
I also got R 140 G 140 B 132 and one additional Idx 162.
don't know what that Idx 162 means.
And thank you everybody for your input.
Best regards
Jusko
don't know what that Idx 162 means.
And thank you everybody for your input.
Best regards
Jusko
This is certainly an interesting thread with a wide range of
answers none of which are probably right. But in the interest of
contribution to the confusion I submit to you the Grey Card from
http://www.kodak.com/US/en/motion/products/tools/card.shtml
If you bring it up in photoshop and use the color picker you will
get the values of R 140 G 140 B 132 (or at least that is what I
got).
So assuming Kodak knows a thing or two about color, I would say
none of us here understands what it takes to make an 18% grey card.
Vernon D Rainwater
Forum Pro
According to the Adobe sRGB color test image (of the Fruit Lady - Carmin Marianda) the Gray chart at the bottom is (RGB 127 - 127 - 127) according to the INFO selection in Photoshop 7.
Could the Kodak values be specifically for some of Kodak Photo Processing Labs and/or Equipment.
--
Vernon...
http://www.pbase.com/vrain
William Robinson
Forum Enthusiast
Apple has a Kodak derived 70% N.D. Graycard which is supplies in digital form for its Colorsync technology. It comes as part of a package called "Calibrated Desktops," which I either found on the Apple Web site or had included in some Apple System install.
I also have an Kodak 18% card.
If I open the Apple Kodak 70% imge in Photoshop and select it with the eyedropped, I can then make it the background gray color when I hit the F key.
Compaired to the 18% card (not scanned) the overall gray depth is the same. The physical card is more neutral in color cast than the digital file. I haven't tried including the card in a photo and then matching that color on screen, which is the intent of the card. but Apple describes the process thus:
N.D. Gray Card 70%
------------------------------
This file has been balanced to a Kodak neutral density gray card viewed in a 5000°K light box. The unique gray desktop pattern is designed to quickly and easily help you arrive at a close balance of your scene.
A 70% neutral density gray card is an important tool for photographers to use for taking exposure measurements. When included in at least one scene (taken on one piece of the same film and processed in the same batch), it is a helpful reference for photolabs to use for getting acceptable color balance on the first print.
Steps for use of the N.D Gray Card 70%:
1) Include the physical gray card in one scene of the image(s) you are shooting.
2) Install the N.D. Gray Card 70% as your desktop picture or pattern
3) OPEN the photograph in any image editing application (i.e. Photoshop).
4) Move the border of the image window until you just begin to crop off one margin of the grey card. You will now easily see the difference in color between the image's gray value and the desktop's gray value.
5) Use the color-balance controls of the image editing application to match the color of the gray card in the scene to the color of the gray desktop. The image will now be reasonably close to its natural color balance.
NOTES:
a) Gray Cards are manufactured by Kodak and others, and available in 8"x10" and 4"x5." They are specifically designed to absorb 70% of the light and reflect 30% of the light (suggesting the average amount of light reflected back from a typical scene).
b) The monitor must be properly calibrated prior to use of the N.D. Gray Card 70%.
william
I also have an Kodak 18% card.
If I open the Apple Kodak 70% imge in Photoshop and select it with the eyedropped, I can then make it the background gray color when I hit the F key.
Compaired to the 18% card (not scanned) the overall gray depth is the same. The physical card is more neutral in color cast than the digital file. I haven't tried including the card in a photo and then matching that color on screen, which is the intent of the card. but Apple describes the process thus:
N.D. Gray Card 70%
------------------------------
This file has been balanced to a Kodak neutral density gray card viewed in a 5000°K light box. The unique gray desktop pattern is designed to quickly and easily help you arrive at a close balance of your scene.
A 70% neutral density gray card is an important tool for photographers to use for taking exposure measurements. When included in at least one scene (taken on one piece of the same film and processed in the same batch), it is a helpful reference for photolabs to use for getting acceptable color balance on the first print.
Steps for use of the N.D Gray Card 70%:
1) Include the physical gray card in one scene of the image(s) you are shooting.
2) Install the N.D. Gray Card 70% as your desktop picture or pattern
3) OPEN the photograph in any image editing application (i.e. Photoshop).
4) Move the border of the image window until you just begin to crop off one margin of the grey card. You will now easily see the difference in color between the image's gray value and the desktop's gray value.
5) Use the color-balance controls of the image editing application to match the color of the gray card in the scene to the color of the gray desktop. The image will now be reasonably close to its natural color balance.
NOTES:
a) Gray Cards are manufactured by Kodak and others, and available in 8"x10" and 4"x5." They are specifically designed to absorb 70% of the light and reflect 30% of the light (suggesting the average amount of light reflected back from a typical scene).
b) The monitor must be properly calibrated prior to use of the N.D. Gray Card 70%.
william
D
digidog
Guest
No such values unless you first specify a working space. RGB is a device dependent color model. So sRGB will have different values than Adobe RGB 1998 for the same color.
--
The Digital Dog
http://www.digitaldog.net
Jusko,
The values you are asking for vary depending on use and color space. The concept of the 18% gray card for traditional photography doesn't always carry over into digital. Make 3 new documents in PS, on sRGB, one Adobe RGB and one ProPhoto. Fill each with 18% gray and then look at the numbers and the visual results.
HTH,
VG
The values you are asking for vary depending on use and color space. The concept of the 18% gray card for traditional photography doesn't always carry over into digital. Make 3 new documents in PS, on sRGB, one Adobe RGB and one ProPhoto. Fill each with 18% gray and then look at the numbers and the visual results.
HTH,
VG
Mike Warren
Veteran Member
Check this out:
http://www.aim-dtp.net/aim/calibration/middle_gray/
Mike
---
http://www.pbase.com/mikew714
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