Difference between revisions of "GIMP/C2/The-Curves-Tool/English-timed"

|Welcome to the spoken tutorial of Meet The GIMP. My name is Rolf steinort and I am recording this is Bremen, Northen Germany.

 

|Now lets start with today's tutorial.It  about curves.

| Let me 1st activate the Curves tool in the tool box and then click in the image. You can see there is a histogram in the Curves tool and here are 2 bars with a gray scale.  

|Then there are some buttons to select in the curves tool like preview, save, open etc. But for now we’ll concentrate on the gray scale bar of Curve tool.  

|This bar here shows the different colour range of the source image. And in this bar we have some pixels which are really dark and some pixels which are really bright and in between there are pixels from dark to light. This horizontal bar here consist of 256 different colour tone. The initial point on this bar is zero which is black and on end point it’s 255 which is white. And for example this here 184 is gray.  

| This image consist lot of colours and I can show you the different colours here by changing the channel. Let’s select red in the colour channel and you can see the red tones in the image. Similarly you can change it to green and blue to get the respective tones. And in this image it’s not very surprising that the green channel is dominant channel which has lot of values in it. Now click on reset channel.   

| The curve of the histogram above each tone is the count of the pixel which have luminosity. And we have an area here where there are almost same number of pixels with this terminal and this terminal on the bar. The histogram shows that here is the highest colour range.  

|02.55

|You go into the image when the curve tool is active and the mouse cursor changes to a little dropper, when I click here, the line in the histogram shifts to that point. You can click into the image and move around to know which tone is where in the image.  

|Now we have covered horizontal bar here. And this here is the output. And here are also 256 different values and they form the image. Horizontal bar contains the data which is put into the curve and vertical bar contains data that is put out. This line in between which crosses the graph is the translation function.  

| 04.03

|I can pull this curve as I want to and when I pull it down you see that the image gets darker. And now when I go up from mid gray to the curve and then go to left, I land at dark gray. You see it here that the lower bar here is the original input and the vertical bar is the output of the curve tool.  

|But if I don’t want to see any bright pixels in the image, so I can pull all the points down and then the image is nearly black. Just pull this point up here and you can get some bright stuff here. You can play around with the Curves tool until you get images that have been in fashion for years ago.

|There are some more buttons in the curves tool like Linear Mode and Logarithmic Mode. In logarithmic mode you get the smaller values pushed up.  

|In logarithmic mode this line can be 1, this 10, this 100 and this 1000. Each step gives you 10 times more value and with this you see the small pixels which in linear mode are hidden, you see it in this corner you can’t say if there are pixels which have value more than 250. But in logarithmic, you see we have pixels over the full range of the image.  

|Then there is save dialog and open dialog button. When you finish with changing the curves you can save it for later use and recall it whenever you want to

|How do I use curve tool in this image. I want to get the dark part of the image a bit darker. I want to keep the mid terms as it is and I want to have bright part a bit brighter. And to do this I think I will use the ‘S’ curve.  

|I just pull the curve in the lower part a bit down and you can see that the dark part gets darker and I go to the bright part and push the curve up and make the bright part brighter. You can pull the curve a bit up for more brightness.  

|When I click ok the values of the curves is stored. And when I repeat this process here, you can see that the histogram has changed. There are no values in between here with no pixels and when I click on logarithmic mode, there also you can see no values for certain pixels.  

|Each time when you use curves tool, you lose some pixels in the image. So don’t try to undo the curve operation by doing the opposite i.e by pulling the curve up here and pulling down here. Click OK and now you can see that it get worst and worst and you end in a image with colour banding.

|I think this was it for this tutorial. And I hope to see you around for the next tutorial.