Creating B&W images

[Ofnuts]

(12-31-2017, 03:08 PM)godek Wrote: How do I know if am image is clipped in a histogram?

The histogram shows a large value for V=0 or V=255. For instance this picture has its highlights clipped (in that case, only where the sun is, so this isn't a problem)(dark line along the right edge of the histogram) while the darks are OK:

   

[godek]

I still don't get it. Could you explain how to read a histogram? I am guessing the black is left and light is to the right and if either side goes beyond the square on the side it is clipped then? What about going up what if it goes beyond the sqaure box is that too clipped or not then what does that signify?

[Ofnuts]

Each pixel has a "Value" (luminosity, more or less), somewhere between 0 and 255. The histogram shows, for each of these possible values of "Value", how many pixels have that particular value. In the histogram posted above, a large number of pixels have a value between 0 and 25, with a peak at V=12. Your normally want an histogram which is somewhat evenly stretched across all values. If it's too much on the left, the picture is underexposed, and too much on the right, overexposed. All decent digital cameras can display the histogram of the picture on the control screen. You can of course have specific histograms for the R,G, and B channels.

See https://en.wikipedia.org/wiki/Image_histogram

[godek]

What's gamma by the way?

Second Question:
Let's say you have to make corrections in gimp first such as red eye removal. Can you save it as a 16bit tiff in rawtherapee then open in gimp make the corrections and then edit in rawtherapee like using the film simulation feature. Or will this ruin the picture? Can I remove red eye in rawtherapee?? I want to make the image black and white in rawtherapee but would like to remove the red eye first before doing that.

[mholder]

Gamma is the middle slider
   
It create a non-linear adjustment to the midrange levels of an image.  IF you adjust the gamma slider, then click 'Edit these settings as curves', then you can see what it looks like on the curves dialog.

Why is it called Gamma?  I don't know.
https://en.wikipedia.org/wiki/Gamma_correction

[godek]

How about this image? Is that a good histogram?

[Ofnuts]

(01-03-2018, 03:28 AM)godek Wrote: How about this image? Is that a good histogram?

Yes, decent...

[Ofnuts]

(01-02-2018, 10:54 PM)godek Wrote: What's gamma by the way?

Second Question:
Let's say you have to make corrections in gimp first such as red eye removal. Can you save it as a 16bit tiff in rawtherapee then open in gimp make the corrections and then edit in rawtherapee like using the film simulation feature. Or will this ruin the

https://en.wikipedia.org/wiki/Gamma_correction

[gramp]

What I do sometimes is create two dupe layers of the original photo layer and then run the Colors->Threshold tool on each, one to find the "edges" where the darkest pixels reside and another to find the "edges" on which the highest-valued pixels live.

You asked earlier "which pixel to pick" with the eye-dropper tool. Using threshold can answer that question. (You can go on to use the threshold layers for other artistic and masking purposes.)