Weird "Dithering" Using Rebel and C1 Pro

[drisley]

I've been using my Digital Rebel and C1 Pro Raw conversion software for a few months now, and I love both!

At Easter, I took my first shots with my new 85mm f1.8 lens.
I absolutely love how relatively noise free the images are at ISO 400 and 800.

Anyway, my nephew was wearing a red shirt, and later after I converted from raw to tiff, I noticed a strange "posterization", "stair-stepping", "dithering" in the shadows of the red shirt...almost as if it was a gif file.
I tried the raw file in Photoshop CS, and it was fine, so it's something with the C1 Pro conversion. I think I remember someone else complaining about this once. I've never noticed this before, so I wonder if it just doesnt like saturated reds?

The image was taken at 1/125s - f2.5 - ISO400 and was properly exposed (no exposure adjustments in C1 Pro). White balance was auto,and it was converted using C1's Rebel profile and destination was Adobe RGB.

I put the full size jpg for viewing here:
Red Shirt (http://www.sharpnsmart.com/temporary/shirt.jpg)

If anyone would like a copy of the raw file, just let me know.

[slejhamer]

Dris, what were your C1 settings for sharpening, noise reduction and banding?

[drisley]

Everything was pretty much at or near default.
I also tried increasing the banding setting to HIGH, but that made no difference.

If you like I can put the Raw file somewhere for you to download.

Btw, I have other pictures taken of my nephew in that same shirt, and they all have similar "banding".

-----------
Sharpening:
Soft Look 80, 3

Banding:
Default

Noise Reduction:
Default (Low +1)

[slejhamer]

If you like I can put the Raw file somewhere for you to download.


Sure, I'll give it a go. You can PM me if you want the location kept private. I'd have you email it but my system has trouble with large attachments.

P.S. I'm not sure it's only the reds, as there is similar "blockiness" in the shadow areas of his cheek and neck. Not as obvious, but it's still there, at least from what I can see on my monitor.

[KennyG]

Could you re-convert the file as sRGB instead of Adobe in C1. Convert to TIF, resize and make the last adjustment convert to JPG? Try keeping the workflow sRGB. I would like to compare the results.

[drisley]

Thanks guys.

Yes KennyG, I did try using other profiles, like srgb, but the problem exists.
In fact the problem is also visible in the C1 preview window too.
Using breezebrowser and photoshop, the problem doesnt exist.
Some people at C1's forum have had a look at the raw, and think it may have something to do with the generic rebel profile included with c1 pro.

Slejhammer, I will pm you with the raw location.

Thanks again
:)

[Loekito]

Hai Drisley, I ever been in that situation before, but I'm forgot whether the problem is happened on PS or C1.

But the one that I remember most, that strange red-color behavior happends only if I'm shoot using Adobe RGB settings on my DRebel. But not if I'm shoot using Parameter1 or Parameter2.

The problem gone when I'm set the color management to Adobe RGB. Maybe It happend, because of the application was not set to use Adobe RGB profile, since it have more wider gamut (correct me if I'm wrong).

Regards,

Loekito

[slejhamer]

Dris,

My C1 preview (using either the main preview window or the "focus" preview) looks nothing like your final image.

Here is a side-by-side:

http://www.pbase.com/image/28145321

Generic Rebel profile, same sharpening and other settings as you used except converted to sRGB. I did think the file needed almost a full stop of exposure comp or levels adjustment (I used the latter) to tighten up the histogram. Oh, this was in C1-LE, but that shouldn't make a difference (though you never know.)

Yes, there is still a minor amount of blocking-up in the shadows, but there is also significantly more detail in the shirt.

This isn't entirely fair, as I'm comparing your web jpeg to a preview of the RAW file just before processing, so how did my processed file look?

Not quite as good after saving for the web, but still nothing like what you posted.

http://www.pbase.com/image/28145324

So where is the problem? I don't have any idea.

I also ran this through Photoshop's RAW converter, and the shadow detail was slightly more pleasant than what C1 produced, but not really significant. However, PS didn't do as good a job on noise removal, and there was a very-visible criss-cross pattern when viewed at 100% or more. I've heard this "ACR noise" mentioned before but this is the first I've seen it, so it could be related to the image ISO and the way the different programs handle noise reduction. Don't know. In any case, the differences were very minor and barely noticeable when not zoomed in.

Well, sorry I don't have answers for you, but I did not get the same result so we can't really blame C1 or the profile just yet, at least not without further review.

[drisley]

Thanks people.

Loekito, yes, I only have my camera set to Adobe RGB, but that should not affect Raw. And yes, my C1 is set to Adobe RBG.

Slejhamer, thanks for going to all that trouble.
I also had the creator of C1 Pro, and one of the users in his forum try the raw file and they produced similar results to yours. They both agreed though that the image needed some exposure comp by about 1 stop too.

But yes, the reds are very different in our results, although the blocking still remains in both.

It looks like I failed to mention that my saturation setting is set to default to +5%. That may in fact be the biggest part of the problem.
I reduced saturation back to 0%, and this brought the image close to your results, with MUCH more detail in the reds. Some blockiness still appears, but not as bad.

I guess I learned something. Don't oversaturated or risk loss of detail!
:roll:

I always assumed it would be better to add saturation in the Raw part of the workflow, rather than later in Photoshop. Looks like I may have been wrong. Then again, I may have added so much saturation that I overloaded the Adobe RGB gamut.

Thanks again slejhamer! I really appreciate it.
8)

[drisley]

Addendum:

Doh! I thought the problem was solved.
When I reduced the saturation, the result looked pretty good in the preview window, much like your result.
But when I saved as a 16bit tif with adobe rgb, and compared the image to the raw conversion using Photoshop CS, the C1 Pro reds looked really bad again.
Here is a side by side, both with default settings, except for a +.60 exposure comp.

http://www.sharpnsmart.com/temporary/shirt2.jpg

[slejhamer]

But when I saved as a 16bit tif with adobe rgb, and compared the image to the raw conversion using Photoshop CS, the C1 Pro reds looked really bad again.

:shock:
Whoa, that's bad. I assume (but have to ask just to be sure) that the two images are in the same color space...

C1 has a known problem (at least for 10D and D-Reb files) with blooming yellows/neon greens. Supposedly it will be fixed in an upcoming release. This makes me wonder if other colors are also a problem, though I have not experienced a problem with reds myself and the issue does not seem to be the subject of complaints on the PictureFlow board. We'll see.

If there is a problem, then Michael Tapes will get if fixed eventually. You did the right thing by sending him your file. Please let us know how it gets resolved. :)

[slin100]

I'm assuming that the web image posted is representative of what you saw in C1. Anyway, it sure looks like Photoshop CS is dithering the output to reduce posterization.

One thing to keep in mind are that the shirt is almost perfectly red, which I've heard is the least sensitive channel. If the C1 RAW converter is anything like the in-camera one then, according to one source, only about 10 1/2 out of 12 bits in the red channel are used. Since the image is underexposed ~2/3 stop, you're not even using all those 10 1/2 bits. In the end, you probably only have a handful of bits covering the shadows.

Also, don't forget that you're viewing the images on a 8-bit per channel monitor, so the monitor is only going to render at most 256 shades of red.

[drisley]

But when I saved as a 16bit tif with adobe rgb, and compared the image to the raw conversion using Photoshop CS, the C1 Pro reds looked really bad again.

:shock:
Whoa, that's bad. I assume (but have to ask just to be sure) that the two images are in the same color space...

C1 has a known problem (at least for 10D and D-Reb files) with blooming yellows/neon greens. Supposedly it will be fixed in an upcoming release. This makes me wonder if other colors are also a problem, though I have not experienced a problem with reds myself and the issue does not seem to be the subject of complaints on the PictureFlow board. We'll see.

If there is a problem, then Michael Tapes will get if fixed eventually. You did the right thing by sending him your file. Please let us know how it gets resolved. :)

Yes, there is definately a problem with the way C1 Pro renders the reds in this (and a few other pics I took of the same shirt) picture.
I also did a conversion with breezebrowser, and again, the shirt looks MUCH better, even better than the conversion with PS CS.

I always use Adobe RGB for my tiffs.

BTW, I also tried using other camera profiles in C1 to see if it was the 300d generic profile. Well, the problem still exists, so that is not it.
Also, do you notice in the C1 conversion (both mine and Slehanmer's), the weird/ugly looking edges of the collar?
Slej, I think you are right, C1 appears to have a problem. Yes, I sent the Raw file in to Michael. I hopes he fixes it.
I have loved C1 Pro so much, but it is really disheartening to see this.
Breezebrowser gives much better results in this case, but I really miss the control (especially WB) that C1 gives.

[slejhamer]

Also, do you notice in the C1 conversion (both mine and Slehanmer's), the weird/ugly looking edges of the collar?


I hate that. See it regularly in C1 conversions. Best to turn C1 sharpening down and then do it in PS...

Speaking of PS, here is an example of the cross-hatch problem I mentioned:
http://www.pbase.com/image/28164483

I've seen it before in some PS RAW conversions and have heard many people deny the problem exists, but there it is. Luminance smoothing reduces it some, but not entirely. C1 does a better job of noise reduction, in my opinion. Of course, it may have problems of its own...

Dris, you are right about BB. We need to figure out a way to merge the Canon conversion engine (which BB uses) with C1's workflow. :lol:

[drisley]

Yes, I too noticed the cross-hatch problem when testing this image.
Very weird indeed.

I totally agree with you.
If the canon conversion engine was used in C1 PRO, it would be AWESOME!

Let's do it! Uh, er, I know nothing about coding... do you? :lol: