Post-Editing Options for HDR Output

[LSI_Morales]

Dear Medikoo,

The difference is actually that you are missing the gamma value when switching from one program to the other. You Should not forget that you monitor is 8 bits but your files are 16 bits, it means a lot more information of that what your monitor is capable of displaying. In that case when switching among applications you will always have to correct the gamma value (apply a curve) to your pictures.

Cheers

[RAG]

I opened file in PS (CS4) made sure it's using Scanner profile (PS by default is using embedded profile). I saved it to other tiff file keeping same scanner color profile..

Did you open the files directly into PS or into Camera RAW (CR)? CR allows you to make non-destructive edits and allows you to pass those changes into PS.

[LSI_Ketelhohn]

Dear mrrafs,

you are right HDR images are using a gamma of 1.0. (this can be changed in the Options)
They are also not rendered into a new target workspace like AdobeRGB or sRGB.
The image will have the scanner's color-space profile embedded.

Multi Exposure is more than bracketing.
It does not just look which image is better of a series.
MultiExposure uses the image data of multiple scans to compose an image of higher dynamic range.

kind regards
Arne Ketelhohn

[medikoo]

The difference is actually that you are missing the gamma value when switching from one program to the other. You Should not forget that you monitor is 8 bits but your files are 16 bits, it means a lot more information of that what your monitor is capable of displaying. In that case when switching among applications you will always have to correct the gamma value (apply a curve) to your pictures.

Yeah, that's true, gamma is the issue. However from what I found, applying a curve won't fix that. I think Problem lies earlier in color processing steps.
Color profile that is embedded within HDR file is not read by Photoshop as it should. Photoshop assumes it has gama 2.08 (in my case), while in reality it is 1.0. This mismatch also make files that got through Photoshop look different when viewed back in Silverfast - Photoshop on save probably adds it's gamma information to image and Silverfast from now on relies on that, and image doesn't look as it has before.

The fix I've found is to make linear (gamma 1.0) profile using Custom RGB option in Photoshop, you just save scanner profile under different name but with gamma set to 1.0. When I created such profile, then assigned it to image and opened that image in Photoshop, everything looked nice as in Silverfast. Photoshop now assumes it's gamma 1.0 and everything seems correct. Correct me if I'm wrong (?)

[LSI_Morales]

Dear Medikoo

However from what I found, applying a curve won't fix that. I think Problem lies earlier in color processing steps.
Color profile that is embedded within HDR file is not read by Photoshop as it should. Photoshop assumes it has gama 2.08 (in my case), while in reality it is 1.0. This mismatch also make files that got through Photoshop look different when viewed back in Silverfast - Photoshop on save probably adds it's gamma information to image and Silverfast from now on relies on that, and image doesn't look as it has before.

Probably you have set SilverFast to save with a gamma of 2.08, for HDR output. This can be done (or undone) by opening "options" and selecting the "general" tab.
Next to gamma value tick the check-box "for HDR output" to export the files with the gamma you have during preview in SilverFast. Or un-tick the check-box to deactivate the gamma gradation and have the HDR files with a linear gamma (gamma value of 1.0)

Gamma gradation and HDR output options

gamma for HDR output.jpg (55.71 KiB) Viewed 5075 times

Cheers

[medikoo]

I have exactly the same settings. I don't have "for HDR output" checked, so it can't be the case.

When you are opening HDR file scanned with Silverfast in Photoshop do you see same colors as you see in Silverfast HDR Studio ? I got much darker colors and I think that's not only me (?) I want to be sure what's the cause - currently I think the cause is that Photoshop assumes different gamma than Silverfast. What do you think ?

[LSI_Morales]

Dear Medikoo,

If you do not have it checked the you are scanning 48 bit HDR files with a gamma value of 1.0 where as you operating system probably has a gamma value of 2.0 or 2.2 and Photoshop is showing you a file with a gamma of 1.0 in a system with a gamma of 2.2

Hence you have to make a gamma correction in photoshop.

Cheers

[medikoo]

LSI_Morales, it doesn't sound right to me.

Firstly as I understand gamma setting is written within ICC profile, and as long as you use profiles that embeds correct information you never need to additionally adjust gamma in Photoshop. My LCD Screen profile embeds info that gamma of my screen is 1.801. When I open image with embedded linear profile, this profile should inform Photoshop that it's 1.0 gamma.. while it looks profile created with SilverFast says it's gamma is 2.0 (Silvefast HDR Studio seems to ignore that info, and treats images as if gamma was 1.0)

Take a look what ColorSync shows for linear profile created with Silverfast Studio:

and for comparison this is what ColorSync shows for other linear profile provided by Minolta with scanner:


I think wrong gamma information within profile fools Photoshop to display image not correctly.

[LSI_Morales]

Dear Mediko

Firstly as I understand gamma setting is written within ICC profile, and as long as you use profiles that embeds correct information you never need to additionally adjust gamma in Photoshop. My LCD Screen profile embeds info that gamma of my screen is 1.801. When I open image with embedded linear profile, this profile should inform Photoshop that it's 1.0 gamma.. while it looks profile created with SilverFast says it's gamma is 2.0 (Silvefast HDR Studio seems to ignore that info, and treats images as if gamma was 1.0)

I will try to make things a bit clearer.
While ICC profiles do have a gamma (As you clearly mention and illustrate with your pictures).
And your HDR files have a profile embedded.
HDR raw files generated with SilverFast do not have the same gamma as the profile embedded.
HDR raw files have a gamma of 1.0 or a linear gamma (unless indicated otherwise by selecting the option I mentioned in a previous post) where as the ICC profile has a gamma of 2,0 or 1,8 or 2,2 (a gamma curve).

The ICC profile of the scanner is embedded into the HDR raw file for SilverFast HDR to automatically recognize the source used to produce the file and activate some resources into the software, however the gamma correction is NOT performed according to the embedded ICC profile, instead SilverFast HDR expects raw files with a linear gamma and apply a gamma curve automatically (the gamma value with which raw files are expected can be changed into SilverFast HDR options).

This gamma correction is NOT done by photoshop automatically, you have to do this gamma correction in photoshop manually as well as the conversion from 16 to 8 bits per channel.

Cheers

[medikoo]

Dear Alejandro,

Thanks, that sounds clearer. However I still don't understand few things

HDR raw files generated with SilverFast do not have the same gamma as the profile embedded.

Why do profile embedded within HDR doesn't have gamma information corresponding to image ?
Is profile totally not related to image, or is it just gamma information.
If so, what's the purpose of having gamma information not match rest of profile ?

The ICC profile of the scanner is embedded into the HDR raw file for SilverFast HDR to automatically recognize the source used to produce the file and activate some resources into the software, however the gamma correction is NOT performed according to the embedded ICC profile, instead SilverFast HDR expects raw files with a linear gamma and apply a gamma curve automatically (the gamma value with which raw files are expected can be changed into SilverFast HDR options).

This gamma correction is NOT done by photoshop automatically, you have to do this gamma correction in photoshop manually as well as the conversion from 16 to 8 bits per channel.

So my understanding is that scanner profile made with Silverfast is in true linear (as device profile should be - gamma 1.0) however for some reason it's meta data states it's gamma is 2.0 - and this is source of confusion. HDR Studio ignores gamma info in profile, and blindly treats it as linear (therefore produces correct results) and Photoshop obeys to gamma information in profile and produces incorrect results.

If my understanding is right, why the confusion with incorrect gamma info is made ?

[LSI_Morales]

Dear Medikoo,

Why do profile embedded within HDR doesn't have gamma information corresponding to image ?

Because the profile is to work with a second color profile for the color matching, and their primary purpose is to not to provide the gamma value but to manage the color

Is profile totally not related to image, or is it just gamma information.

The profile is related to the device used to scan the image and was created with a different image (actually a target)

If so, what's the purpose of having gamma information not match rest of profile ?

I think you are confusing individual images with color profiles.

The profile is created to work with a determined device (in this case a scanner), but the scanner is not working alone, there is a computer system which needs another color profile standard to the whole system and your monitor, which also has its own color profile.

Information passing through from one device to the next needs to be transformed to match the colors.

The scanner profile (which you have embedded into HDR files) does not correspond to the system color profile.

All this is independent from the gamma value of your image (or that of any color profile) because the gamma value of your image can be manipulated independently

This transformation is made automatically by SilverFast HDR whereas in photoshop this process has to be performed step by step and manually controlled by you. If you simply let photoshop convert your files to any predetermined working space, it will likely show your colors off.

So what you want to do in Photoshop would be:
-Open the HDR file with a gamma of 1.0 (linear) preserving the embedded color space
-Apply a gamma correction (so far I know, there is not a gamma value correction in photoshop, you might want to use levels to correct this with the value in the middle of the slider)
-Make a conversion to Adobe RGB
-Further adjustments
-8 bit conversion


Cheers

[medikoo]

Dear Alejandro,

Thanks for reply. I know about all things you mentioned. I understand color management. I know that device (scanner) profile doesn't correspond in any way to monitor profile and that image needs to be transformed from one color space to another to have it displayed correctly - however this wasn't my concern. Maybe I didn't express my self clear enough, so again my question is:

Why meta data within scanner profile created with Silverfast states that profile gamma is 2.0 and not 1.0 ?

We all know that it's device profile created using IT8 target, we know that this device is linear and it's gamma is 1.0 - why there's misleading info within that it's gamma is 2.0 ?

I understand that this makes confusion and is source of not correct display in Photoshop. You suggest to correct gamma with levels in Photoshop. I'm asking why scanner profile that is embedded with file doesn't provide correct information about profile so Photoshop could show images with correct gamma right away ?

[LSI_Muenier]

Dear Mediko,

a scanner ICC profile (created with SilverFast or other software) should be usable with image data of 16bits depth as well as 8bits depth.
But when working with 8bits (i.e. 24bits RGB) image data, you would not want them to be at gamma=1, but at gamma=2.2 (or similar, in synchrony with your working space) to avoid creating histogram gaps when you finally will convert the image to gamma=2.2 or similar.

Therefore we chose to create scanner profiles for usage with image data at a certain gamma value (i.e. not directly for linear image data),
usually this is 2.2 (for synchrony with AdobeRGB and best approximate to sRGB).

SilverFast HDR or DCpro internally handle both image types, with bit depths 8 or 16, in the same manner and automatically correct:
- first, the image is converted to the user's gamma (only if needed, which is the case for the linear HDR images)
- then the color space conversion is performed from the embedded (scanner) color space to the working color space
(thus, the scanner ICC profile is used on the image data which are no longer linear but alredy have the gamma)

This is made sure by a special tag in the scanned image file, which allows SilverFast HDR or DCpro to "know" the gamma already applied.
Unfortunately, Photoshop cannot interprete this tag, and therefore applies the scanner ICC profile directly to the linear image, which the scanner ICC profile was not meant for.

Proposals for solution:

(1.) When working with SilverFast HDR or DCpro, then your images will be color matched correctly (as described above).

If you want to work with Photoshop on linear HDR scans from SilverFast:

(2.) If you have the IT8 calibration option within your SilverFast scanner version, than you may alternatively create a gamma=1 scanner ICC profile for your scanner. For achieve, please set the gamma value in the Option's "General" panel (of the SilverFast scanner version) to gamma=1 before starting with the IT8 calibration process. Then you will get an ICC profile usable with gamm=1 (linear HDR) image data, only. Please remember to restore your gamma in the SilverFast scanner version to 2.2 or what you had chosen before.
Once you have the gamma=1 scanner ICC profile, you can assign it to your linear HDR images when opening them in Photoshop.

(3.) In future, you may choose to write HDR image data from your SilverFast scanner version "with gamma included", so you would check the corresponding CheckBox next to the gamma value in the Option's "General" panel to achieve that.

(4.) For the HDR scans you already have (and which have gamma=1, as I understood), you can convert them in Photoshop as Alejandro described, or you may use SilverFast HDR or DCpro to convert them from HDR with gamma=1 to HDR with your desired gamma.

I hope that I have made clear why our profiles are for "gamma-applied" image data and not directly usable for linear image data.
SilverFast HDR or DCpro automatically handle the SilverFast-scanned HDR images correctly, regardless of the gamma in the image.

Best regards
Martin Münier

[medikoo]

Dear Martin,

Great thanks for that explanation (!) I missed that knowledge.
So I understand that by default scanner profile created with Ai Studio is good for images with already applied 2.2 gamma.
Silverfast HDR recognizes whether image data had gamma applied or not by specific meta tag. PS doesn't recognize this tag and hence the confusion.

Looking this way, I think that proposed solution (2) will be best for me, seems also most clean and not destructive, as right away I will have linear profile and linear image data that will be understood correctly with both Photoshop and HDR Studio.

Thanks for help !

[LSI_Muenier]

Dear medikoo,

perfect, I think now we got it!