# Tag Info

16

Curves is a powerful and very flexible tool, which allows to control brightness, contrast and color balance very preciesly. The way I approach the curves tool, either in Gimp or in any other editor is two-fold: (1) The curve defines how to change the intensity. Its left side is for the darkest parts of the image, its right side is for the brightest part of ...

15

The curves tool stretches or compresses ranges of input tones according to the line you draw. Because it represents a mapping, it's nonsensical for the line to go backwards horizontally — which means you can't possibly draw a "proper" S — you have to draw one that is tilted (that is, slanted) to the right. These examples are in grayscale because you can ...

12

Levels are a special case of curves, where the curve is pinned at both ends and has one control point in between. The two pairs of "input levels" and "output levels" specify the coordinates of the end points of the curve. The "middle value" specificies the degree of curvature. Levels can only have one radius of curvature, so the curve you posted is not ...

10

The GIMP's curves tool is virtually identical to PhotoShop's Curves tool. Almost all photo manipulation tools have a way of doing that action. There are a number of good explanations of it out on the internet if you look for photoshop: http://www.google.com/search?hl=en&q=curves+adjustment+in+photoshop this one however is fairly thorough in it's ...

7

Use 2 points to create an 'S' shape in the curves editor. See: http://www.chromasia.com/tutorials/online/curves/images/basic_s_curve.jpg So basically the curves editor is a chart. For each pixel in an image, its brightness is represented by a number from 0 to 255. 0 is pure black, 255 is pure white, and everything in between is a shade of grade gray. ...

7

Yes, your assumption is correct. A levels control is basically the equivalent of a curves control that can only be adjusted at the end points and one point in the middle, while a contrast slider is (usually) the equivalent of moving both ends at the same time (although some may be more sophisticated). The curves tool gives the most flexibility, but also ...

7

Just perform regular post-processing. For reference, here is your first picture with all the boarder fluff stripped off: Simply making the darkest spot black and the lightest white fixes a lot: The snow looks a little yellowish, so here I'm using one area of the snow that looks like it should be white as the white balance reference. I also brought ...

5

The Base curve is used to alter how the raw light data is interpreted. You can think of this almost as the input curves in other apps, they control how the raw data in the file gets pulled into the image editing space. This is often where fancy curves are used to simulate different types of film and such... that's very much what it's doing, adjusting the ...

4

You are right that curves is the way to increase detail at certain brightness levels. The steepness of the line dictates contrast (and hence detail). You only have so much "height" to play with so making the line steeper in one place (e.g. the shadows) means it must be shallower elsewhere. If you're careful you can make the line shallow in an unimportant ...

3

I look at them kind of like sandpaper for a woodworking project: The Contrast slider is the really coarse paper that you use to get in the ballpark of the final shape you want, the Levels sliders are like a medium grit that allows you to fine tune the shape and get closer to your goal, and then the Curves allow the finest control like a really fine grain ...

3

The basic answer is that you can only modify with curves (do not use levels) If and only if you do have the primary color component on the mix, and you can only shift the colors to some degree. You can not in this case: Here is an example image with some clear colors. I separated the channels and you can see for example that I only have information on the ...

3

Here is what I did: Given the input file with one number per line: 0 ... 17 18 18 19 20 21 22 ... 244 244 245 246 246 247 247 248 ... 255 I copied it into Spreadsheet, divided each number by 255, and formatted all the values to 6 decimal places. After that, I edited a saved Gimp curve, removed the ...

3

Although the color information loss is clearly not avoidable in this kind of 8-bit transformation, you can have a better behaving image if you accept a bit of a loss in sharpness... I do not know in other programs, but in darktable you can use t he module "dithering": I tried the same trick on a small jpeg image, and this is the result: before: and ...

3

Reid. Don't throw your blacks into the pits of despair! Just don't tone so aggressively. That's the easy answer. Here's the more involved answer. I'm not sure what your end game is: print, web, tele, all have different sensitivities. But the general approach I would use goes like this. Process your RAW as you have, then hop into PS (I did my best to ...

3

RawStudio tends to have a very low-contrast default curve. I find that pictures are quite muddy and it takes a bit of adjusting to make them punch. Generally I start by creating a node near the very bottom (dark) end and pulling it down for contrast, and then creating a node near the midtones and bringing it up. Hard to explain exactly what shape I'm ...

2

Heres an article for the curves tool in Photoshop. The ideas should be the same in all tools. http://www.cambridgeincolour.com/tutorials/photoshop-curves.htm Here's another one which talks about curves for different colour channes: http://www.bairarteditions.com/pages/tutorials/photoshop/cbcurves.html

2

Yes, you can replace levels with curves. I don't think there is an exact mathematical consistency in the definition of levels, but each level corresponds to a portion of the curve from left to right and will boost or drop it based on the value. I don't know that q factors are published or consistent, but normally they cover roughly 25% of the spectrum with ...

2

When you view a RAW image, what you are actually seeing is a conversion of a RAW image. This is true whether you are looking at it on the screen on the back of your camera or on your computer screen, because the screens themselves are not designed to display more than an 8 bit per color dynamic range. Your camera, depending on model, probably records RAW ...

2

Two reasons: Because we don't see linearly and our brightness resolution sucks. Look at a gradient in 8 bit (256 grey values): http://www.tftcentral.co.uk/images/dell_2408wfp/gradient_grey.jpg We see about 16 grey patches and the two ends are most compressed for us. It's not until value 30-50 we start seeing details. So a lot of objects can be hidden or ...

2

An 8-bit image will most likely have its pixel values truncated. What you need to do is interpolate the missing low order bits before applying a colour transformation. There is no way to know what the missing values are, you would have to make certain assumptions, such as smoothness. To answer your question I don't know of any image editor that offers this ...

2

From a theoretical point of view there is no "True" way of getting those values back. convolution kernels (like guassian smoothing, or an edge preserving kernel) and dithering will make assumptions to bring them back, rank filters may not (like median). However, there is no way to "know" how those values should have been before the quantization, so it is a ...

2

Description of the format can be found in video.gimp.windows.user usenet group archive, if that's any help. The syntax of the file is apparently some dialect of Scheme.

2

You can't, easily, because hues other than pure red, green, or blue are made of mixes of those colors. If you want to increase or decrease the proportion of one of these in a constant way, the levels tool will work. If you want to increase or it only in highlights or shadows, or in an area that's got a particular cluster of a certain brightness of that ...

1

RGB is fine for minor changes such as going from blue to cyan, but if you want to make major changes you should learn how to work in LAB. LAB's separation of color from luminosity into two distinct opposing channels makes it easy to change one color into any other color using a combination of channel blending and curves. For example, I was able to change ...

1

The contrast is low. If you open up curves in Photoshop, and take the point on the bottom left and drag it up, you'll notice that hazy look becoming more apparent. To keep the black tones however, also take the middle point and drag it down a bit to bring shadows back in, and experiment until it looks how you like. As for the color, a simple warm photo ...

1

You should apply the LUT to each channel. If you are really interested in image processing theory, then you should start a new question asking for book recommendations on the subject, if it hasn't already been asked.

1

For next time, you might want to take a closer look at your manual to figure out how to improve capture. Snow throws off most auto camera settings, and many cameras now have an automatic snow/beach mode to adjust (or at least an exposure adjustment setting), but if you understand what's going on even the basic adjustments available on your camera can be ...

1

Hokay, Turns out I was over-thinking the problem (no way!). The answer is values from Curve1 go through Curve2. So on the RGB100 -> RGB50 a R100 value becomes R50, then in the R100 -> R125 curve the R50 value becomes R73. Voila.

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