Episode 200: Worldwide Pinhole Photography Day

tip of the pin
Download the Video! (7:15, 63MB)

And here is the mythical Episode 200 – in a quite different form than planned. Years later, shabby audio and short. I am still on a steep conversion course with my workflow – and completely out of routine. Even the video is partly out of focus….

This Sunday (tomorrow!) is the Worldwide Pinhole Photography Day.

In the video I demonstrate a quick and dirty way to convert an expensive digitial camera to a cheap quality pinhole camera.

Episode 201 will cover the background for this stuff – but this has to go up now!
Meet the GIMP Video Podcast by Rolf Steinort is licensed under a Creative Commons Attribution 4.0 Unported License.
Permissions beyond the scope of this license may be available at http://meetthegimp.org.

Episode 195: Whose RGB?

rgb
Download the Video! (24:09, 80.6 MB)

Download the Companion File! (14.8 MB)

Watch at YouTube

Colo(u)r ist the topic this time. You are in for a ride from the electromagnetic spectrum to the biology of color vision and the infamous Mantis Shrimp. (Link to the fabulous Oatmeal!)

Grassmann’s Law gives a clue how to create a color sensation in the brain by mixing up some wavelengths out of the spectrum. The CIE finally defines what is visible for a “Standard Observer” and Microsoft & HP (sRGB) and Adobe (Adobe RGB) build their color spaces on that foundation.

Elle Stone, Bruce Lindbloom and Cambridge in Colour help along the way, passing a Black Body emitting radiation according to Planck’s Law at 6500K just to give us a White Point.

Then I organize a shootout between sRGB and Adobe RGB – and I’ll stick to sRGB for the forseeable future.

Finally I cover the question of Intent while converting between different color spaces – Perceptual or Relative Colorimetric?

Links

Elle’s fine writeup about All the Colors.

The Color Space Viewer (at the bottom of the page)

Pascal’s tutorials about color management on Linux – really hands on:

https://encrypted.pcode.nl/blog/2012/01/29/color-management-on-linux/
https://encrypted.pcode.nl/blog/2013/11/24/display-color-profiling-on-linux/
https://encrypted.pcode.nl/blog/2013/04/14/display-profiles-generated-from-edid/

The TOC

00:00:00 Intro
00:00:15 Submit to GIMP Magazine
00:00:50 Light as part of the electromagnetic spectrum
00:01:43 Biology of color vision
00:06:14 World Champion of Color Vision: The Mantis Shrimp!
00:06:40 Grassmann’s Law – mixing colors from spectral primes
00:07:22 CIE 1931 Color Space – the standard observer
00:09:00 Elle Stone’s blog – a lot about color!
00:09:50 sRGB
00:11:40 D65 – the White Point for sRGB
00:11:56 Black Body Radiation and White Points
00:13:44 Bruce Lindbloom has a Color Space viewer
00:14:30 Adobe RGB (1998)
00:15:50 Why not ProPhoto RGB?
00:16:20 Preparing some test shots in the lab
00:16:59 Comparing sRGB and Adobe RGB camera setting
00:18:42 Conclusion – stick to sRGB
00:19:34 Converting between color spaces
00:20:06 Intent: relative colorimetric or perceptual?
00:21:14 Consequences
00:23:10 Winding down
00:24:09 EOF

Meet the GIMP Video Podcast by Rolf Steinort is licensed under a Creative Commons Attribution 3.0 Unported License.
Permissions beyond the scope of this license may be available at http://meetthegimp.org.

Episode 134: Dynamic Range T(h)errory

Download the Video! (37.8 MB, 19:53)

The German word “Terrorie” was coined by a kid in a Physics lesson of my late colleague Helmut Mohr in Hamburg. It is what it sounds like – and today’s video is full of it. No GIMP, no images, only the blackboard and me talking. Please consider this as a WARNING. 😉

We had a lively discussion in the forum about the theory behind making images, circling around the term “dynamic range”. There is a big difference between light and dark parts of our world, often more that a camera can catch. And nearly always more than fits onto paper or a computer screen.

The process of squeezing this big range into the small output range is called Post Processing. Either you do it via RAW anf GIMP – or the smart chip in your camera does it while saving your iage as JPEG. What I forgot to say – if you do it, you can redo it. The RAW file still exists. If the chip does it, the RAW file is discarded and you are stuck with the version of the image made by the chip.

I got a lot of information about this subject from a wonderful paper by Karl Lang at Adobe(R). Worth to download and read, even if you decide to skip the video this week.

The TOC

02:04 Orders of Magnitude
04:00 How much light is in a scene? (Dynamic range ramp up)
06:00 There is no black and white
06:30 Dynamic range of a scene
06:50 Dynamic range of LCD and prints
08:50 Dynamic range of the camera
09:50 Exposure = slide the dynamic range
11:05 Post processing by the camera
12:15 RAW -> GIMP -> print
13:00 Slides and egatives in analog photography
15:05 A source at Adobe(R)
15:15 8 Bits – a problem (sometimes)
17:10 Why is it possible to make images? Because our eyes are no camera and our brain no computer.

Creative Commons License
“Meet the GIMP”  by Rolf Steinort is licensed under a Creative Commons Attribution-No Derivative Works 3.0 Germany License.
Permissions beyond the scope of this license may be available at http://meetthegimp.org.

Episode 124: PS Translation Service

Adobe(R) Photoshop(R) Screenshot(R) Download the Video! (53.7 MB, 28:14)
Download the Video for iPods etc (24.1 MB, 28:14)

There are a lot of tutorials out there for “The Other Program”, also called Adobe(R) Photoshop(R). (I hope I got the Rs right, can’t find the page where Adobe(R) told the world how to call this program.) A lot of that stuff is easily translated to GIMP, but there are some serious differences. One are the “Adjustment(R) Layers(R)”. This is a way of applying a curve, gradient, hue or saturation change…..  without changing the real image. You can come back later and tweak the curve or the slider – non destructive editing.

There is an easy way to work around this: make a new layer of the visible image and work on that. You have to redo that, if you decide to change something in the lower layers.

To show how to do this I have ripped out a part of John Arnold’s Photowalkthrough podcast and redone the same in GIMP. Photowalktrough is a really good resource for everybody who is into the digital darkroom – independent from the program used. And John has his #100 out! Congratulations!

GIMP will have non destructive editing in a year or two – it’s the main reason for getting GEGL into GIMP and making this big effort of writing a lot of the program again.

In the second part of the show I get the blackboard out and start a new segment in the show. I try to explain how  film and sensors are working. I’ll expose you to some of these lessons for about 5 to 190 minutes and will then decide upon your reaction if I should keep this on. I’ll have them at the end of the show – if you are bored you can just skip the rest.

Sorry, there is no TOC up to now. the moment Kevin made one. 🙂

The TOC

00:28 Welcome to PhotoWalkThrough.com from John Arnold
01:05 Welcome to Meet The Gimp from Rolf
02:30 Back to John
02:50 – a curves layer
05:10 – a layer mask
08:20 Back to Rolf
09:00 The original photo
09:20 Make a layer with increased saturation
10:40 Add a gradient layer in soft light mode to alter the sky
12:10 New layer from visible
13:25 Add a layer mask and edit it
15:25 The problem with destructive editing
15:55 But it’s not that big a problem
18:20 New segment – time for lessons
19:55 How film works
24:00 How a sensor works
27:00 Feedback please
28:14 The End

Creative Commons License
Meet the GIMP Video Podcast by Rolf Steinort and Philippe Demartin is licensed under a Creative Commons Attribution-Share Alike 3.0 Germany License.
Permissions beyond the scope of this license may be available at http://meetthegimp.org.