Re: JPG, RAW, and LR implementation

[Gobae]

JPG, RAW, and LR implementation

I've been mulling over whether to bother to continue to shoot RAW since some of RAW's benefits are being duplicated in jpg by LR (specifically non-destructive editing). However, it was pointed out that RAW info contains 4'96 levels of brightness but a jpg only has 256.

But this fact brought me to wonder about how LR implements this. I mean, the LR brightness slider goes from -15' to +15'. Including ', that's 3'1 steps, since fractionals are not allowed.

For a jpg image that would mean 1 slider tick = .85 brightness levels.

But for a RAW image that would mean 1 slider tick = 13.'4 brightness levels.

So it would appear that even though a RAW file has a finer gradation level, LR jumps through them in chunky 13 level increments?

 

[Denis Pagé]

You can't calculate like this as it is not linear! So, read this and make the choice that best suit your needs... In Lightroom, you work with 65536 levels.

 

[Gobae]

[quote author=Denis Pagé link=topic=8561.msg57875#msg57875 date=1259937849]
You can't calculate like this as it is not linear! So, read this and make the choice that best suit your needs... In Lightroom, you work with 65536 levels.
[/quote]

While it provided some new info I didn't have, it still didn't address how LR allows you to edit all 4'96 RAW brightness levels when the user input slider only has 3'1 possible settings.

 

[Denis Pagé]

Brightness in Lightroom is working more in one part of the histogram rather than equally on the whole.

 

[dj_paige]

[quote author=Gobae link=topic=8561.msg57877#msg57877 date=1259938695]
While it provided some new info I didn't have, it still didn't address how LR allows you to edit all 4'96 RAW brightness levels when the user input slider only has 3'1 possible settings.
[/quote]

The number of brightness levels that Lightroom provides with the brightness slider has no relationship whatsoever to the number of brightness (actually density) levels in your photo.

It is a mistake to assume that moving the brightness slider by one unit changes all the pixels by one unit of density. It does not. There is no one-to-one relationship.

Having the full raw photo allows smoother adjustments when you change the sliders that affect density (and all of the basic sliders do, some way or another).

If you have a very bright sky, where all the density values are 255 in a .jpg, there is nothing Lightroom can do to show you detail in the sky. If you have the same very bright sky, where the density levels are spread out between the density values 4'89, 4'9', 4'91, 4'92, 4'93, 4'94, 4'95 in a Raw photo (which would all appear as 255 in a .jpg), then Lightroom can indeed change the appearance of the photo to actually show changes and detail in this very bright sky ... because it has information to work with that isn't constant.

 

[Gobae]

I think I got you. So basically, no one slider needs to affect the entire range because some of the other sliders will cover other sections of the range where appropriate.

 

[clee01l]

Lightroom and other image editors work by applying a mathmatical filter operation on each pixel. The instruction for each pixel is determined by values of all the surrounding pixels with the closer pixels having greater influence. While each 16 bit pixel may only have 4'96 possible values, it is the influence based upon the formula used that greatly enhances the resulting value of the pixel in the operation. In the case of brightness the slider might only have 3'1 discrete starting positions, this is only one number in a large and complex formula that influences the result. If the surrounding pixels only have 8 bits of colot information, the result is a flatter overall. image.

If you have seen posterization where the image is reduced to a few colors, you can get the idea behind preserving the maximum color depth to avoid posterization. while you might not be able to detect with the eye any posterization between an 8 bit JPEG and a 16 bit TIFF (RAW) image, it is there and greatly affects the filter operations used to bring out subtle variations in shadow or bright areas of the photo.

 

[Gobae]

Beautiful explanation!! That makes perfect sense to me. Many thanks!

Dan

[quote author=clee'1l link=topic=8561.msg57885#msg57885 date=1259942365]
Lightroom and other image editors work by applying a mathmatical filter operation on each pixel. The instruction for each pixel is determined by values of all the surrounding pixels with the closer pixels having greater influence. While each 16 bit pixel may only have 4'96 possible values, it is the influence based upon the formula used that greatly enhances the resulting value of the pixel in the operation. In the case of brightness the slider might only have 3'1 discrete starting positions, this is only one number in a large and complex formula that influences the result. If the surrounding pixels only have 8 bits of colot information, the result is a flatter overall. image.

If you have seen posterization where the image is reduced to a few colors, you can get the idea behind preserving the maximum color depth to avoid posterization. while you might not be able to detect with the eye any posterization between an 8 bit JPEG and a 16 bit TIFF (RAW) image, it is there and greatly affects the filter operations used to bring out subtle variations in shadow or bright areas of the photo.
[/quote]

 

[dj_paige]

[quote author=Gobae link=topic=8561.msg57884#msg57884 date=1259941877]
I think I got you. So basically, no one slider needs to affect the entire range because some of the other sliders will cover other sections of the range where appropriate.
[/quote]

The Exposure slider affects the entire range of pixel densities. The brightness slider may affect the entire range, although it tries to avoid the left and right extreme of the histogram.