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How can I change all pixels of one color to another color in a picture?

I have an image which looks like this:

However, the yellow line needs to be red and the cyan line needs to be green. I have Paint and IrfanView. How can I change the colors of the yellow and cyan line without individually selecting all pixels manually?

That is, what is a good way of changing all pixels of one color to another color?

How to make transparent background of a gif animation?

I have a gif animation with white background.
Is there a simple way (e.g., free or shareware application) to remove this white background and make it transparent?

Is it possible to apply Photoshop adjustment layers to multiple raster layers?

I have something like this:

Raster Layer 1
Raster Layer 2
Adjustment Layer
Raster Layer 3
Raster Layer 4

I want to apply the adjustment layer to the raster layers below it, "rasterizing" it basically, so that the pixels in layers 3 & 4 are changed based on the adjustment layer. I don't want to modify the layer stack in any way. That is, no creating or removing layers. Layer 3 and 4 must stay exactly as they are, just the pixels in them should be changed. I don't want to do this one layer at a time, is this possible in Photoshop CS4?

How can I 3D-rotate an image around the y-axis in Photoshop?

How can I use Photoshop in order to rotate a bitmap image on the y-axis? I'm trying to make it so that the right side of the image will go "into" the screen, and the left side will go "out" of the screen.

How do I remove the background from an image?

I have a logo:

and I'd like to get rid of that yellow-ish background once and for all and perhaps even change the whole logo to black instead of green. is there a way to accomplish this with Paint or GIMP?

I imagine getting rid of the corners is simple, but what about the inside?

Convert grayscale image into alpha channel image in unix shell

I have a gray-scale image. I want to convert it into an transparent PNG, such that the black pixels (in the original image) become fully opaque, the white pixels become fully transparent, a 50% grey pixel would become 50% transparent, and so on for all the shades in between.

How can I achieve this?

(Yes, I know that this is almost the same question as Converting grayscale shades into alpha channel, but I want to know how to do this using only command line tools – e.g. ImageMagick or NetPBM.)

How do I edit photos to defeat facial recognition [closed]

Is there a way to alter solo or group portraits to make faces recognizable to or identifiable by humans (their friends), but not by facial recognition software (by Facebook, etc.)?

Open Source image editor that handles PNG Alpha transparency correctly? [closed]

I want to be able to take a sample image, and be able to fade out the background.

For example, I might take a picture of a bird. Make most of the background almost completely transparent, and have a smooth transition to full opacity adjacent to the subject.

Most of all, I want to be able to save / export to PNG.

MS Paint for Gnome

I want an MS Paint like program for GNOME.

GIMP is too much for me. I find it very frustrating for the simple tasks I do (adding text, arrows and circles to screenshots to highlight different features of a program).

Image editor that allows multiple, separate, simultaneous crop selections to be saved? (looking for both free & paid programs) [closed]

Is there an image editor that allows you to select several crop regions and save each one as an individual file? Rather than having to load up the original image each time and do the cropping of each area and saving.

This would be useful if you are using the master, original image for several new purposes, or if you are scanning in several separate items at once.

"Security" Issue: Retained Cropped Screenshots

I made the worrying discovery today that after cropping a screenshot in Word, PowerPoint, and probably other Microsoft Office programs, the rest of the cropped screenshot is retained. This has made me fairly paranoid as I frequently take screenshots and crop them down to show the relevant piece of information, before sending the PowerPoint off to others. I assumed when you saved the document, the cropped portions of the image were discarded, but looking at work from years ago, I can still uncrop the rest of the image to see my entire screen.

Is there a way to disable this? This seems like a ridiculous security flaw.

Rotate a picture by a small number of degrees

Sometimes when I take a picture of a rectangular object, it comes out rotated by a small number of degrees (less than 5 or so).

I can make the space where the rectangle isn't white or whatever, but how can I select a non-rectangular (in the sense that it does not line up with the four ninety degree angles that I am given when I use a rectangular select tool), and rotate it by this small number of degrees?

Additionally, if I could "stretch" one end of the rectangle because it got skewed to match the height of the other one, that would be great. I realize that there will be some loss of resolution if it do it this way (though just as good would be a way to "compress" the other side, and that would not reduce the quality of the image).

I am pretty flexible on the program (GIMP, Paint.NET, Paint, and Visio), but I am open to downloading any free software that can do this.

What's the state of the art in image upscaling?

I like to collect cool pics and use them as wallpapers or for other things. Often, artists publish only low-res versions, probably for fear of theft.

Example:

Now, if I want to use that as a wallpaper, I'd have to upscale it, and obviously that'd make it look blurry because of the bicubic interpolation. I realize there's no real way to get a high-res version from a low-res pic, because the information is simply not there.

That said, I'm wondering if heuristics have been developed for upscaling with less apparent loss of quality. Those would probably be optimized for specific image types. For photorealistic pictures, for cartoons with large flat areas, for pixel art...

One algorithm I'm aware of is Seam Carving. It works for some kinds of pics, especially ones with a plain, undetailed or uninteresting background, and a subject that strongly stands out. But it's far from being general-purpose. Applying it to the above pic produces this. It looks quite sharp, but the proportions are horribly distorted because the algorithm is not designed for this kind of pic.

Another is Pixel art scaling algorithms. Those are completely unfit for anything other than actual pixel art that's pixelized to begin with. For example, I tried the scale2x windows binary on my pic, but its output was nearly indistinguishable from nearest-neighbour scaling because the algorithm didn't detect any isolated pixely fragments to work from.

Something else I tried was: I enlarged the image in Photoshop with bicubic interpolation, then I applied unsharp mask. The result looks pretty bad. The red blotch is actually resized reasonably well, but the dove is far from it.

What I'm looking for is some app that makes a best-effort attempt at upscaling any input image while minimizing blurriness. If you know of any, I'll be thankful. Note that the subjective prettiness and sharpness of the result is what matters... the result doesn't need to be completely faithful to the original small image.

Is it possible to make a .png (or other) image that does NOT have rectangular dimensions?

This might be a dumb question, but is it possible to make a .png file that isn't square?

If so, how can one do this in Gimp?

Ideally I'd like one in the shape of an X.

Auto image enhance for Ubuntu

F-Spot had an "enhance" button that magically turns the image on the left into the image next to it (see below). It worked brilliantly for quite a range of images. Unfortunately it has problems, and I'm not using it for photo management any more.

Does anyone know of a similar excellent "enhance" function? The one in Shotwell is useless.