Histograms.

Exercise: Histogram.

For this exercise I used my Canon G1X as its live screen and histogram are easy to see and use.  

Mid contrast.

For the mid-contrast pictures I used a run down byre.  The grey of the byre itself was similar in tone to the ground on which it stood and the sky was not too bright.

I took the three required pictures.

The picture taken as the camera suggested had a well centered histogram with little at the extremes but a well defined start and finish.  The white house in the background and the pitch black interior of the byre account for the edge details.  The whites do not reach 255 and the blacks are short of 0.  All within range.

At one stop over the histogram had kept its shape but now had a warning at the right edge showing that there was some highlight clipping.  A quick reading with the Digital Colour Meter confirmed this with the white houses reading the full 255 for RGB.  Even the chalky soil was registering in the 240/250 region.  Most of it would be recoverable but not the true shade of the houses.  When I took the shot the camera was showing a gamut warning for these highlight

areas.

In one shot under the histogram had kept its shape but had moved over to the left and showed a warning at the left edge indicating a loss of detail at the dark end.  This can be seen clearly in the screen shot with the blue gamut warnings in the shadow of the byre.  Even the dark windows of the houses have the same gamut warnings.  Again a reading with the DCM confirms that these blacks are registering 0 for RGB.  Most of this picture would be recoverable but these true blacks could not be brought back.

High contrast.

For the high tone I photographed a field of Holstein cattle.  Their contrasty colour, plus the black and white of the farmhouse, cover the full range from true white to true black.

The suggested reading gave the following.  The histogram is further to the left than I would have expected but it still shows some clipping to the right.  A quick check with the DCM shows that white of the house is slipping out of gamut.  The black of the cattle is nice and deep and well into the low numbers on the DCM and slight signs of clipping.  There was no sign of clipping on the histogram at the shadow end.

The one over shot showed a similar histogram but shifted to the right.  The highlight warning is more pronounced, which I confirmed with the DCM.  The white in all the buildings had slipped over the 255 mark and even the white on some of the cattle had gone as well.

The one stop under shot displays clipping marks all over it.  The histogram is well over to the left but has retained its shape. It has a small warning line indicating that some shadow detail has been lost.  Most of the shot could be recovered but not the lost shadow detail.

Low contrast.

I made a number of attempts to take an attractive low contrast but in the end settled for a picture of a wall.  The wall lacks both dynamic and colour range.  Not attractive but perfect for this exercise. 

The suggested exposure has a neatly centered histogram with smooth slopes on each side tapering down to the base line.  This is almost a sine curve.  No clipping warnings.

The one stop over showed a similar sine curve but it was both moved to the right and bent to the right.  I was not as aware of this bending on the earlier examples but in this purer curve it became so.  There was a small clip warning to the right of the histogram but the DCM failed to find any point that had truly burned out.  Although wrongly exposed the picture would be recoverable.

The one stop under shot gave a near perfect set of sine curves.  No clipping was visible, and although dark would be perfectly recoverable.  There was no lean to this histogram.

In the three examples here there was more clipping at the highlight end.  This was even so in the low contrast picture.  

I took two more pictures for myself of the cattle.  The cameras histogram indicated I should shoot at a 1/3 stop under.  This produced an exposure pretty much on the money.   I have learned in the passed that it is often better to slightly under expose that to risk burning out the highlights.

I had a general awareness of histograms before this course but was not not of their subtlety or their colour function.  I will certainly make more use of them in the future.