Lightroom vs RAM: How many MB per MP?

[Jim Kasson]

I think he's referring to using the L* to create auto generated edge masks in the Detail panel...also note that sharpening (and luminance noise reduction) are applied to the luminance data only. I'm not 100% sure it's L* but I think it is.

Jeff,

Here's a way to do sharpening in luminance on an RGB image: http://www.google.com/patents/US5793885

I'm not saying that Lr does it that way, but you certainly don't have to go to Lab to do luminance sharpening.

..so, I'm not sure how you would separate out the L* of L*a*b* if you don't actually convert to Lab, do you?

Starting with a pixel in linear PPRGB, multiply the red value by 0.288040, the green value by 0.711874, and the green value by 0.000086, and add the results together to form a quantity that we'll call Y. Convert from Y to L* by applying the appropriate non-linearity, which is mostly a cube root function with a straight line portion near zero.

If an approximation is sufficient, take 3/4 of the green value and 1/4 of the red value and add them together. Right-truncate to 8 bits, and use that to index into a 1D LUT to get L*.

[Added later: even more approximate, but even faster. Take the 7 MSBs of the green plane and the 5 MSBs of the red plane and use them to index into a 2Dx1D LUT that gives you L*. Or even cruder, take the 8 MSBs of the green value and use that to index into a 1D LUT that gives you L*.]

There are several options in between the above two [three] in both accuracy and computational complexity.

Jim

[Schewe]

I'm not saying that Lr does it that way, but you certainly don't have to go to Lab to do luminance sharpening.

I'm not saying LR does it that way...I was just trying to expand on what Eric said...that LR/ACR does certain things that require processing to move out of RGB (or CIE XYZ). For specifics, you'll need to ask Eric.

[PhotoEcosse]

Could you explain what you mean by this as in my view this explanation or rationale is pretty meaningless.

If you read through the thread from the beginning, you will understand.

[Jim Kasson]

I was not stating that they produce copies of the whole image in all those spaces at once, but you can't apply LUT /dcp LUTs/ unless for each pixel you do the trip from ppRGB/g1 to HSV and back for example... I was saying "you might assume that there is a moment when the same image data is presented in RAM in 2+ spaces at once" - may be just in 2 (and not 3+)... certainly you can have a range of tricks to avoid that (for example replacing pixel related data in place, in exisiting memory structure, instead of in a newly allocated memory structure, etc)...

Yes, I see. My comments have been in the context of conversion of the entire image, which is what I think is the long pole in the tent for the Lr memory footprint issue.

As an aside, and possible something worthy of some research,  Eric Chan informed me some time ago that there are two image-processing pipelines in Lightroom: output-referred, and scene-referred. Raw files and 32-bit floating point TIFFs get the scene-referred pipeline. Integer TIFFs and JPEGs get the output-referred pipeline. Many of the Lr tools work differently on the two pipelines. Therefore, it's possible that the considerations involved in Lr memory footprint may be different for these two classes of files.

Jim

[deejjjaaaa]

As an aside, and possible something worthy of some research,  Eric Chan informed me some time ago that there are two image-processing pipelines in Lightroom: output-referred, and scene-referred. Raw files and 32-bit floating point TIFFs get the scene-referred pipeline. Integer TIFFs and JPEGs get the output-referred pipeline. Many of the Lr tools work differently on the two pipelines.

I 'd assume those are not parallel, but somewhat sequential within one workflow/pipeline... scene referred exists till you do a first color transform from raw RGB to anything else (note that EC 'd say "...I would argue it's still scene-referred colorimetry because each RGB coordinate still has a linear relationship to the non-white-balanced camera coordinates. In other words, the interpolated camera -> XYZ matrix is providing a scene-referred colorimetric interpretation of what those captured camera RGB values mean..." - I'd assume his position is that only a non linear operations like 1-2-3D LUTs applied somewhere make something non scene referred)

[hjulenissen]

Because, in terms of data processing, a "pixel" is not a unit of data. It can be referenced by data in different ways in different software on different machines for different purposes.

Sorry but that answer did not make much sense to me either.

Can you give us any hints that you know what you are talking about?

-h