Recovery slider

[Jeremy Roussak]

There's something rather magical about seeing blown areas, displayed in that red highlight which is so depressing to see, disappear as the recovery slider is moved to the right. But I'm curious: what is LR actually doing? Where is the information which allows the "unblowing" to take place coming from?

Just wondering - I don't need to know to enjoy it!

Jeremy

[bjanes]

There's something rather magical about seeing blown areas, displayed in that red highlight which is so depressing to see, disappear as the recovery slider is moved to the right. But I'm curious: what is LR actually doing? Where is the information which allows the "unblowing" to take place coming from?

Just wondering - I don't need to know to enjoy it!

Jeremy
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Jeremy,

A full explanation is beyond my level of expertise, but I will make a try. LR uses the Camera Raw engine for raw conversion, and in previous versions of ACR, highlight recovery involved use of the exposure slider. The whites are most likely to blow, and with overexposure all channels do not blow simultaneously, because of white balance. If you are using daylight, the values for green in the raw file are quite a bit higher than those for blue and red. White balance is achieved by applying a multiplication factor to these channels. The factor varies with the camera, but with the Nikon D200 it is 2.06 for the red and 1.6 for the blue for 5200K. Other Nikons and the Canons are not that much different.

Therefore, the  green channel in the raw file blows first (in white or gray areas), but the red and blue channels may well be intact. since they are to the left in the histogram. The exposure control decreases all channels by a linear scaling factor and values for the blown channel can be reconstructed from data in the intact channels, and an algorithm is used to maintain color balance. If all three channels are blown, highlight recovery does not work well.

Sometimes the overall image became too dark when the exposure control was used to recover the highlights. The new highlight recovery slider in ACR (and LR) addresses this problem. If the image is overexposed with blown highlights, one uses the exposure slider to bring the overall appearance of the image to where it should be. If the highlights are still blown, one can use the highlight slider to decrease the highlight values selectively, effectively compressing them. Again, a special algorithm maintains color balance.

According to Bruce Fraser (in his ACR book), one can often recover from a half to full stop of overexposure, depending on the camera. I don't think that highlight recovery would work with JPEGs or TIFFs.

I hope this helps.

Bill

[Jeremy Roussak]

Jeremy,

A full explanation is beyond my level of expertise, but I will make a try. LR uses the Camera Raw engine for raw conversion, and in previous versions of ACR, highlight recovery involved use of the exposure slider. The whites are most likely to blow, and with overexposure all channels do not blow simultaneously, because of white balance. If you are using daylight, the values for green in the raw file are quite a bit higher than those for blue and red. White balance is achieved by applying a multiplication factor to these channels. The factor varies with the camera, but with the Nikon D200 it is 2.06 for the red and 1.6 for the blue for 5200K. Other Nikons and the Canons are not that much different.

Therefore, the  green channel in the raw file blows first (in white or gray areas), but the red and blue channels may well be intact. since they are to the left in the histogram. The exposure control decreases all channels by a linear scaling factor and values for the blown channel can be reconstructed from data in the intact channels, and an algorithm is used to maintain color balance. If all three channels are blown, highlight recovery does not work well.

Sometimes the overall image became too dark when the exposure control was used to recover the highlights. The new highlight recovery slider in ACR (and LR) addresses this problem. If the image is overexposed with blown highlights, one uses the exposure slider to bring the overall appearance of the image to where it should be. If the highlights are still blown, one can use the highlight slider to decrease the highlight values selectively, effectively compressing them. Again, a special algorithm maintains color balance.

According to Bruce Fraser (in his ACR book), one can often recover from a half to full stop of overexposure, depending on the camera. I don't think that highlight recovery would work with JPEGs or TIFFs.

I hope this helps.

Bill
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Yes, I think it does: thanks.

I had formed the idea that it was using the information in the non-blown channel(s) to reconstruct the channel(s) which had blown. Your explanation suggests that it's more akin to a special curves adjustment, but including a colour balance correction. I suspect we're talking about rather similar things.

Jeremy

[jani]

I had formed the idea that it was using the information in the non-blown channel(s) to reconstruct the channel(s) which had blown. Your explanation suggests that it's more akin to a special curves adjustment, but including a colour balance correction. I suspect we're talking about rather similar things.

It seems like the colour of neighbouring pixels may be taken into account, at least sometimes.

The pictures below are crops of an out-of-focus area with blown highlights. The exposure has been adjusted by -1.28, but the "Recovery" slider still fiddles with the values before the exposure correction, which allows us to see the effect more clearly. The recovery slider is at 100 for this example:

[attachment=2653:attachment][attachment=2654:attachment]

[The View]

I am very careful with the recovery slider.

I have the impression it dulls the image by dulling the highlights (those, that are not blown).

[Christopher]

I am very careful with the recovery slider.

I have the impression it dulls the image by dulling the highlights (those, that are not blown).
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Yes it kind does, most of the time works great from 10-50 but I would nearly never go over a vaule of 50.