jpg is darker than the dng photo

[David Averbuch]

In Ps I 'export/save for web' a photo that I converted to b&w in camera-raw.

The generated jpg is darker than the dng photo. Why?

[D Fosse]

You have not checked "embed color profile" in Save For Web. You need to make sure that is always checked.

Is this monochrome sRGB, or is it grayscale (single channel)? If the latter, you need to be very careful about using the appropriate grayscale icc profile. If you take your eyes off the ball, you can quickly get tonal shifts.

Outside the Photoshop environment, support for grayscale profiles is very unreliable. Grayscale, even tagged with the correct grayscale profile, can be treated in a totally random and unpredictable manner. For this reason, I usually advise against using grayscale, unless you know what you're doing.

Generally, all grayscale profiles have different tone curves, but some of them correspond to standard RGB tone curves as follows:

sGray = sRGB = Display P3/Image P3

Adobe RGB = Gray Gamma 2.2

ProPhoto RGB = Gray Gamma 1.8

Don't use the Dot Gain profiles at all. They are outdated generic profiles for offset print, not used anymore. Today you use the black ink component of standard CMYK profiles.

[David Averbuch]

1. Checking "embed color profile" didn't change the result.

2. I converted it by clicking on the b&w button at camera-raw. Where do I see if it is monochrome sRGB or not?

[D Fosse]

Then it goes to Photoshop as Gray Gamma 2.2 by default.

In any case, the reason for this is a profile disconnect somewhere, a profile either missing or not read correctly. If it's a grayscale profile, lots of applications won't honor the profile.

I don't know everything that happens here, but retrace your steps and watch the profiles on the way.

It may sound like a paradox, but with grayscale, correct color management is absolutely crucial.

[David Averbuch]

The b&w photo that was created in camera-raw had color space grey-gamma 1.8.

When I changed it to 2.2 the jpg looked I intended it to be - as the dng. 

Where was I suppose to set it to grey-gamma 2.2?

When should I use 1.8?

[D Fosse · Accepted solution]

Short answer is you shouldn't. Gamma 2.2 is much safer, because even without proper color management, it matches a monitor's native behavior well enough so that it should look roughly right in most circumstances.

But my advice is still to not use grayscale, because support in other applications is so uncertain. Inside Photoshop you'll be fine as long as the profile is embedded. But there is an inherent problem even there, because the default working gray is Dot Gain 20%, which is obsolete and doesn't match any current output destination. So without an embedded profile, it goes wrong right off.

Use grayscale with care and attention. One valid use case is for black-plate-only offset print, but then you will use the K component in the appropriate CMYK profile.

[David Averbuch]

I only have a modest blog of photos, and rarely print.

Thank you.

[edited by moderator]