Shots for and from the videopodcast "Meet the Gimp!".

Black & White

littletank   April 13, 2008, 03:40 PM

I intend to spend some time and effort working on the subject of changing colour images into black and white. I am wondering whether there are any other members who would be interested in joining with me so that we can help each other progress and improve our technique. I know there is a group for monochrome but I have confidence in the members of this group in both advice and constructive criticism. Also my interest in this topic was started by the founder of this group and I owe it him to make a start here. I shall post any images I may produce both here and on the monochrome group.

 
xemoth   April 13, 2008, 09:53 PM

I presume you have seen http://www.gimp.org/tutorials/Color2BW/

Also the Math Map plug-in, http://www.complang.tuwien.ac.at/schani/mathmap/

could be useful.


Owen

 
littletank   April 14, 2008, 10:07 AM

Thanks for the references and, yes, I am aware of the first one but not the second. I have been following the videos on meetthegimp.org and especially Numbers 32, 33 and 34. I think I know how to produce black and white images from colour but, what I am not sure about, is whether the results are any good. Things like, have I chosen a suitable subject, or even a suitable image and is my black and white rendering good, bad or indifferent. I think that I shall only be able to improve if there are constructive criticisms of my efforts.

 
Mainzelmann   April 14, 2008, 08:31 PM

Unfortunately I had chosen ipernity as a host for my photostream before finding out that tehre is such a nice community herearound. Nevertheless your request has made me think whether my b&w "performance" has increased over time and so I have collected a set http://www.ipernity.com/doc/mainzelmann/album/60885 about it. I would be happy to jointly learn and improve b&w be it here on 23 or on ipernity. Let's share and comment.

 
littletank   April 15, 2008, 01:09 PM

I can see that I have some way to go before I shall be comfortable producing black and white images. I had a look at some of your images on ipernity and there was one of a wall, I think, with the sun just behind a top corner. There were 2 very small white dots in the sky which you wanted identifying. I would love to have details of that shot such as the time of day, date, location and orientation. They could be stars and the detail would enable to have a look in a star chart to see if that were possible.

 
Mainzelmann   April 15, 2008, 05:10 PM

Pic was taken 2008.02.24 14:39:52+01:00 in St. Leon Rot, Germany, geo-coordinates 49.241671,8.640447. The direction was, well, directly into the sun ;-) (sorry, no planetarium software on the notebook I am using here).

Often I have spent a night under the stars with my telescope, so the first thing I checked was whether there would be bright stars around. Cannot remember exactly but there was definitely notthing around of more than, say, mag 3 and a star or planet would have needed more than that to be seen in that bright day.

When re-thinking, I guess that those lights must be internal refelctions from the camera, either from the shutter or the iris or something similar.

But I would absolutely appreciate could you cross-check the sky at that time. There are, btw, much more than just two such points (I did count 8, but I had to scroll a lot so I migtht have missed one). They can be seen when you create an ipernity account and look at the 2750 full resolution.

Thanks for caring,
Dirk

 
littletank   April 15, 2008, 06:25 PM

You are quite right about stars most of which were about mag 3 or less. However, not all that far away from the sun were both mercury and venus which had not yet set. I suppose because the camera was shielded from the direct sunlight it might have been possible to see venus but not much else.

In the old days we would have blamed bits of dust on the negative and spotted out the blemishes on the print.

 
littletank   April 16, 2008, 10:42 AM

Having looked again at your album I note that while you have many different kinds of picture you are missing an example of 'bas relief'. I realise that a suitable image is needed and I will have a look to see if I can find one amongst my old images. I know how to produce a sort of bas relief with a colour image using GIMP but I have yet to try with b&w.

 
Bill Kehrman   April 16, 2008, 10:26 PM

I remember doing this in a darkroom 100 years ago. Take a B&W negative and make a contact negative (positive) with it. Develop and lay the two together with a slight offset.
I just tried i GIMP with a shot of a crowded desk. I desaturated it to B&W, Then duplicated the layer. I then inverted the top layer and set transparency so I had a completely gray image. Then I used the move tool and shifted the top layer in the x and y direction.
Interesting look.

 
Bill Kehrman   April 16, 2008, 10:36 PM

I just posted the sample I did in my folder on this site.
Have fun.

 
jgsack   April 16, 2008, 10:48 PM

Isn't that a starting point for high-pass filters as well?
Except that the high-pass also uss some blur, and maybe uses a blending mode (instead of onversion?).

Hmmm, could use some help here, from image processing experts.

Anyway, these things are enormous fun (and time-eaters!) to play around with.

..jim

 
Bill Kehrman   April 17, 2008, 12:11 AM

It looks like you are right on both counts. A high pass filter and a time consumer.

 
Alec_Burgess   April 17, 2008, 03:17 AM

@rollab:
Interesting variant on your technique ...
Take any picture. Dup background and change Opacity to 50% - result is gray image.

Nudge copy on x/y: result bas relief

Copy base to dup-2, copy dup-1 to dup-3 then desaturate dup-2 and dup-3. Resulting layer stack
dup-3 B&W, opacity 50%, nudged x/y
dup-2 B&W, opacity 100%, not moved
dup-1 color, opacity 50%, nudged x/y
base color, opacity 100%, not moved

Turning off and on layers 2,3,4 gives interesting variants. I like background and dup-3 ON - gives bas relief with tinge of colour. see Flamingos-orig and Flamingos-bas-relief on my page.

http://www.23hq.com/Alec_Burgess/photo/3039168?album_id=3039167
http://www.23hq.com/Alec_Burgess/photo/3039172?album%5fid=3039167

 
littletank   April 17, 2008, 07:52 AM

I am amazed at the ingenuity around this place, fantastic and greatly confusing to simple, little me. Just a point, in the old days a lot of bas relief producers firstly made a copy onto Lith film thereby getting a loss of mid tones, I think and then go through the process described. Now, using GIMP how does one reproduce this?

 
PhotoComix   April 22, 2008, 09:44 PM

well in the old days i used for bas effect not 2 lith slide but 1 lith and a duplicated slide with higher contrastthen the original...2 lith one positive 1 negative created instead a Line art effect.

The filter most close to lith is the threshold filter but is not the same thing (if not of very simple images)

And even if i try most of script and plugin (including PS plugin) for line art i never find anything offering the same clean but detailed result of a new negative created by a sandwich of 2lith slide one positive one negative.
(result is not fully blank as you may suppose, slides as a bit of depth and some diffration so light would pass )

About the bas to me was important use positive and negative of different density , if density wass too similar result was somehow too flat

 
PhotoComix   April 22, 2008, 09:56 PM

OOOPSS whatching the examples now i saw that i mean something different for bas-relief effect.

I intended a bas relief effect where deep shadows and highlight where still present and not only 2 slightly different shades of grey.

that in a darkroom was possible with a sandwich of 1 very high contrast Negative and one lower contrast Positive

 
littletank   April 23, 2008, 09:04 AM

What I understand by Bas Relief is a form of sculpture where the images emerge from the background and stay attached to the background. Have a look in Wikipedia where there are some good examples.

 
Rolf Steinort   April 23, 2008, 03:16 PM

Very interesting talk in this corner here...

I did a bit of such stuff as a teenager and a bit in my early twenties. So you have to help my mind a bit back on track. Lith film gave very hard images with a lot of black, a lot of white and just a bit of midtones, right?

Then it can be done with the curves tool. Just make a very strong S-curve.

 
littletank   April 23, 2008, 05:49 PM

I know this is slightly off the point but I must mention another application of lith film. Many years ago (about 40 years) some of us played with sandwiching a colour transparency with a lith negative of that slide. Also, by slightly offsetting the positive and negative interesting outlining effects could be obtained. I have experimented with GIMP and I believe that I can reproduce the effect digitally.

 
PhotoComix   April 23, 2008, 07:00 PM

@ Rolf that is correct if you process that with dedicated chemical

But was a cool trick, use old paper developing chemical, then most of the black outline reamained as usual but some degree of gray was simulated by a very cool a clean grain


@till now i fail to reproduce the most interesting effect as

1 line art (2 lith negative+positive as sandwich with perfect register...diffraction create a very clean but detailed line art effect..require much longer exposure then usual)

Bas relief (1 lith negative + 1 (more or less undersposed) positive) as i said difference is very great then the example:
a full tonal range from white to black is mantained enancing so the depth.

i lost most of my older work but i may try to search some survived example

 
Rolf Steinort   April 23, 2008, 07:35 PM

I just played a bit.




 
Bill Kehrman   April 23, 2008, 11:25 PM

What I used was microfilm. That would be high contrast with little mid tones. is that the same as Lith?

 
andrewagill   April 29, 2008, 08:54 PM

I can talk about what little I know about lith film in the printing industry.

Lith film is still around and used extensively for the metal plates in offset lithography.

Hence the name. The concept is that in lithography, the ink is either at 100% or 0%, and thus they cannot have any shades of grey. Grey is simulated using halftone dots. (so when you want 50% grey, you get a series of 100% black dots covering half of the page)

In cases like this, lith film is invaluable. In fact, I just came back from visiting a printer who is using state of the art printing techniques. They use a computer-guided laser to transfer the image to the plate... and then run it through lith film developer.

(dunno if this helps)

 
Bill Kehrman   April 29, 2008, 11:00 PM

Yes thanks. It sounds like they both are similar. The old microfilm was for capturing B7W documents for archival purposes. But then that is what amateurs :) are for to extend the limits of what others think is limited.

 
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