C'mon Fuji - Please Give Us A Proper R G B Histogram!

Started Feb 5, 2013 | Discussions thread
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Trevor G Veteran Member • Posts: 6,558
C'mon Fuji - Please Give Us A Proper R G B Histogram!

I always recommend to use the histogram when shooting, because:

1) it lets us know beforehand how the exposure is likely to turn out;

2) it lets us know afterwards how well the exposure has turned out.

Well, it should but it doesn't, because it is only an L (luminance) histogram on all current Fuji cameras.

It lacks any information about the individual R G B channels. It is quite possible for any or all of these channels to clip (and thus distort the colour information) before the luminance channel shows clipping in the histogram.

A clipped R or G or B channel can turn a blue sky to cyan, or a red rose to pink or green grass to yellow and you generally won't know it till you look at the image later on a proper monitor. Sometimes you won't get the opportunity for a corrective shot.

Here are some examples of how the existing L histogram can fool us if we don't know what to look out for.

The luminance-only histogram on the right duplicates what we see in-camera - it looks under-exposed. However, the RGB+L histogram on the left shows us exactly what each channel is doing, and red is already ever-so-slighlty clipped.

For best noise and contrast/dynamic range we always expose as far to the right as possible, but without clipping.

The in-camera Luminance histogram on the right suggests that we are under-exposing. However, in PP but not while shooting we can see in the RGB + L histogram on the left that the red channel is already starting to clip - see the spiking just before the end.

Here is what happens if we increase exposure to make up for what appears to be under-exposure:

The in-camera shows what looks like a reasonably exposed image (see L histogram on right) but when we examine the JPEG we see that the red channel is well and truly clipped (steeple-like spike on RH end). This results in the yellow render on the clock tower just below the clock turning to cream (in colour).

If we adjust exposure to get a fully exposed image (according to the in-camera histogram) we will get over-exposure because the red channel clips and changes the colour tone of parts of the image.

Unfortunately my test subject does not evoke cries of horror at this stage because at this point the cream render does not look too out of place.

However, in many circumstances, especially with flowers or other landscape features or even a portrait with bright facial lighting, the effect can be quite noticeable because we know what the real colour should have been.

Do other cameras come with full RGB + L histograms? Yes, absolutely.

Have Fuji ever done it before? Yes, but not well. In the S5 Pro they provided full histograms, but you had to click 5 or 6 times to see them because they only showed 1 channel at a time.

The usual version is L only, followed by RGB or even RGB + L, and always beside a large thumbnail so you can see what it refers to.

Come on Fuji, you can do it!


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Trevor G
Silkypix tutorials at: http://photo.computerwyse.com

Fujifilm FinePix S5 Pro
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