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Photo Retouching "Improving" photos, post-production, correction, etc.

Color corrections LAB or RAW

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  #11  
Old 07-26-2011, 09:53 AM
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andrewrodney andrewrodney is offline
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Re: Color corrections LAB or RAW

Much of the issues that need to be ‘fixed’ by moves into Lab are able to be addressed when you render the raw data. Not all but many. There are significant advantages to doing all the heavy lifting you can do in the raw converter and its here that Dan and I strongly disagree! He feels you should zero out the slides, produce a butt ugly rendering and fix that in Photoshop (if all you know is a hammer, everything looks like a nail).

Raw processing is pixel creation. Never forget GIGO:GARBAGE IN GARBAGE OUT. Being careless in a raw converter is akin to the photographer who improperly exposes his film, then has to fix that in the lab/processing. Not ideal. But then Dan’s not a photographer...

The advantages to doing all the work possible in a raw converter is its totally, fully non destructive. You are creating metadata instructions that tell the converter how to build ideal RGB pixels.

Creating metadata is far faster than altering existing pixels. Think about it. You are not altering numeric values of millions of exiting pixels, you are building a text file.

As a raw converter improves, as does the rendering. In Adobe products, we just saw a significant increase in image quality between the 2003 and new 2010 PV processing (noise reduction, demosaicing, just flat out, visually superior). Want that better processing? Easy. Render the raw using the existing settings.

Raw processing is JIT processing meaning, you build the millions of pixels only when you need them. Photoshop is a memory and processor hog because no matter what you want to do there, it has to deal with millions of pixels. For pixel editing, that’s necessary, no question. But for a lot of image processing its not.

All the processing is done in an optimal processing order. Unlike Photoshop, where you can really hose the data or trip yourself up if you don’t process in the correct order, it doesn’t mater at all in Adobe raw processors. You can play with exposure, then saturation or vibrance, then go back to Exposure. The order makes zero difference because when you render the data, Adobe will process the edits in the optimal order. All in high bit, wide gamut color to maintain as much data as possible.

Of course there are tools that require Photoshop, no question. But for 95% of all global and more recently, even selective color and tone editing, you can do it better, faster, cheaper in a raw converter. That’s why we capture raw data too, for the control we have over rendering. Once you render an image, there are things you either can’t do effectively or at all in Photoshop (hint, just try taking an ugly JPEG shot with the wrong white balance and fix that in Photoshop versus using a white balance tool in the raw converter on the raw. Huge differences here).

Don’t build turds and then spend hours fixing them in Photoshop unless you get paid by the hour and need to find ways to build turds. Produce the best possible data with the raw converter before you even think of bring Photoshop to the party.
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  #12  
Old 07-26-2011, 09:55 AM
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andrewrodney andrewrodney is offline
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Re: Color corrections LAB or RAW

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Originally Posted by Tony W View Post
ACR was around at the time he wrote the book no idea which version. As far as I remember he spent no time in ACR and gave the impression that he dismissed it as not being valuable.
Guilty as charged. That alone is oh so telling. OK, now here did he put that hammer....
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  #13  
Old 07-26-2011, 10:31 AM
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John Wheeler John Wheeler is offline
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Re: Color corrections LAB or RAW

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Originally Posted by DWThomp View Post
Do you go from one to another and then back again? Ex. - start out in RGB, switch to CMYK for some correction, and then back to RGB. Is there any harm doing that. I usually stay in RGB, but will change the sampler readout to CMYK at times.
Hi Dennis, I am responding to your specific question about round trips from RGB to CMYK color space. I do not do round trips to CMYK color spaces and also just use the color sampler readout. The reason, virtually all CMYK color spaces have a much smaller color gamut (and visually noticeable in many images). Doing a round trip to CMYK will compress many colors to that smaller gamut and it will remain there on the return trip to RGB.

Even if your original image in RGB only has colors that exist in the CMYK color space there is something different in translating to CMYK and back than with other color spaces (I can provide the reference if that were really needed). A round trip from RGB to CMYK (with no other edits) does not do a great job of preserving the pixel numbers.

If you really want to do a round trip to CMYK, there are ways to minimize such impacts yet that would be the topic of another thread.
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  #14  
Old 07-26-2011, 11:07 AM
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Tony W Tony W is offline
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Re: Color corrections LAB or RAW

Andrew, your first post really made me laugh . Not the overall information about why RAW should be used, which IMO is spot on rather it was your comment 'Don't build turds...'. Having at times throughout my life resorted to semi professional turd polishing I can tell you it gets you nowhere slowly . Sorry but I just could not resist adding comment.
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  #15  
Old 07-26-2011, 06:04 PM
bart1986 bart1986 is offline
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Re: Color corrections LAB or RAW

haha great comment about the turd! But very true! I finally ended up by taking the information about LAB and bringing colors closer together by steepening the curve, that idea i liked and i think it is quicker than in RGB, but defiantly not impossible or better IMO. That idea i'll keep in the back of my head, the rest of the stuff i believe is RAW stuff and stuff i might as well do in RGB
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  #16  
Old 07-26-2011, 10:57 PM
kav kav is offline
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Re: Color corrections LAB or RAW

Not to derail this but has anyone ever found a truly compelling reason to bother with LAB? I messed around with it back around photoshop 6 (I think it was 6) but LAB to me seems best used for referencing colors rather than working in photoshop. Not all rgb/cmyk gamuts contain the same colors but you can pretty much reference them in terms of LAB numbers. I'm not sure what the advantage would be in choosing to actually work within such a space in photoshop.
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  #17  
Old 07-27-2011, 08:58 AM
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Re: Color corrections LAB or RAW

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Originally Posted by kav View Post
LAB to me seems best used for referencing colors rather than working in photoshop. Not all rgb/cmyk gamuts contain the same colors but you can pretty much reference them in terms of LAB numbers. I'm not sure what the advantage would be in choosing to actually work within such a space in photoshop.
Lab has been around long, long before Photoshop. And yes, that’s its original purpose, as a device independent (kind of) color space for communicating color in an almost non ambiguous way. And its been tweaked over the years due to faults in its design and math.

Keep in mind that Lab was just an attempt to create a perceptually uniform color space where equal steps correlated to equal color closeness based on the perception of a viewer. The CIE didn't claim it was prefect (cause its not). Most color scientists will point out that Lab exaggerates the distance in yellows and consequently underestimate the distances in blues. Lab assumes that hue and chroma can be treated separately. There's an issue where hue lines bend with increase in saturation perceived by viewers as an increase in both saturation and a change in hue when that's really not supposed to be happening. Further, according to Karl Lang, there is a bug in the definition of the Lab color space. If you are dealing with a very saturated blue that's outside the gamut of say a printer, when one uses a perceptual rendering intent, the CMM preserves the hue angle and reduces the saturation in an attempt to make a less saturated blue within this gamut. The result is mathematically the same hue as the original, but the results end up appearing purple to the viewer. This is unfortunately accentuated with blues, causing a shift towards magenta. Keep in mind that the Lab color model was invented way back in 1976, long before anyone had thoughts about digital color management.
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  #18  
Old 07-27-2011, 09:08 AM
kav kav is offline
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Re: Color corrections LAB or RAW

Now I remember you mentioned this before. What makes a good reference space now? I still do see measured print values referenced by LAB at times. Is there a better way to reference said values from a larger space(note my post in no way suggesting working on your images in LAB)?
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  #19  
Old 07-27-2011, 09:13 AM
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andrewrodney andrewrodney is offline
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Re: Color corrections LAB or RAW

Lab is a good reference space because the numbers are fixed in stone (they describe how we humans perceive a color). In sRGB, 0R-255G-0B is a different color than the same values in ProPhoto RGB, or Adobe RGB (1998), or myepson3880RGB. A Lab value doesn’t behave this way, the values describe how the ‘standard observer’ perceives that solid color. So Lab is super useful in color management, for converting values among color spaces and so forth. Its the universal translator of color values because its device independent unless you consider the standard human observer a device.
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