Home · Register · Join Upload & Sell

Moderated by: Fred Miranda
Username  

  New fredmiranda.com Mobile Site
  New Feature: SMS Notification alert
  New Feature: Buy & Sell Watchlist
  

FM Forums | Post-processing & Printing | Join Upload & Sell

  

Archive 2017 · Black point changed when converting to SRGB

  
 
memoria
Offline
• •
Upload & Sell: Off
p.1 #1 · p.1 #1 · Black point changed when converting to SRGB


Is there anyway to keep the black point/shadows untouched when converting from AdobeRGB -> SRGB? I have a bunch of portraits which I've developed in DPP and used Adobe RGB. Then, in PS I've worked on them and converted to BW. Then, when finalizing for save I convert them to sRGB and suddenly blacks appear just a tad darker. Which can be confirmed by looking at the histogram (pushed a bit to the left). I'd say The blacks are lowered 6-8 points.

Any ideas? Conversion method Perceptual with black point compensation on.








Jan 29, 2017 at 05:01 AM
skid00skid00
Offline
• • •
Upload & Sell: Off
p.1 #2 · p.1 #2 · Black point changed when converting to SRGB


Try something other than perceptual.


Jan 29, 2017 at 09:08 AM
John Wheeler
Offline
• •
Upload & Sell: Off
p.1 #3 · p.1 #3 · Black point changed when converting to SRGB


I don't think that should happen n a properly set up system.

Note that the histogam is not a good indicator because as I understand it, it just shows the RGB values. If you change color spaces, the RGB values do change so you would naturally see a histogram shift even though there may be no visual shift.

In your case, I have seen gray scale shifts if ASSiGN was used instead of CONVERT or if using soft proofing and the "Preserve Color Numbers" box is checked. It can also happen if the image is not assigned a color profile i.e. not color managed.

It could also be that you have out of gamut colors that when remapped to sRGB gives the perception of a grayscale shift (which cold also be a calibration issue).

Mabye you could create a link to your original Adobe RGB image for others to take a look as well.

I don't know root cause to your issue yet hope the above thoughts give you something to consider.



Jan 29, 2017 at 09:30 AM
Zenon Char
Offline
• • • • • •
Upload & Sell: Off
p.1 #4 · p.1 #4 · Black point changed when converting to SRGB


I gave it a try using both using Relative Colorimetric which what it is always on and Perceptual. I work in ProPhoto and I got a shift in the histogram for both but I did not notice any major change between the two images.







Before







After




Jan 29, 2017 at 09:59 AM
Peter Figen
Online
• • • • •
Upload & Sell: On
p.1 #5 · p.1 #5 · Black point changed when converting to SRGB


For RGB color space conversions using matrix (vs LUT) type of color space profiles, the conversions are always Relative Colorimetric no matter what you select in the dropdown menu. The reason that there is a slight shift in the numbers is that you're moving from a larger color space to a smaller one and what you're seeing is gamut clipping in the near blacks. What would have been a black with marginal detail in Adobe RGB is closer to zero in sRGB. I've done tens of thousands of these conversions over the years and it's never been an issue visually, although the numbers to change a bit. You can easily see what happens by placing info palette probes in areas of interest prior to the conversion and noting the pixel values before and after.


Jan 29, 2017 at 12:37 PM
Zenon Char
Offline
• • • • • •
Upload & Sell: Off
p.1 #6 · p.1 #6 · Black point changed when converting to SRGB


Thanks for the explanation. Makes sense when going from a larger colour space to a smaller one. I often use save for web and make sure the convert to sRGB is checked.


Jan 29, 2017 at 01:26 PM
memoria
Offline
• •
Upload & Sell: Off
p.1 #7 · p.1 #7 · Black point changed when converting to SRGB


Thanks for feedback guys, and I too agree that it kind of makes sense about the colorspace. But still, I don't see how a black and white image needs any reduction/re-mapping when going to a smaller space? Is that due to the different clipping points in the space?

Anyway...I agree that it is not really visible to the naked eye. I can spot it if I look carefully though and I just didn't see the reason for it.



Jan 29, 2017 at 03:56 PM
Peter Figen
Online
• • • • •
Upload & Sell: On
p.1 #8 · p.1 #8 · Black point changed when converting to SRGB


I'm guessing it's because the profiles are not content aware. They only see the entire gamut of the profile and using a Relative Colorimetric conversion, it's always going to map to the closest equivalent in the destination space. You could try an sRGB v4 profile, which might make a difference.


Jan 29, 2017 at 05:41 PM





FM Forums | Post-processing & Printing | Join Upload & Sell

    
 

You are not logged in. Login or Register

Username       Or Reset password



This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.