When you make a gradient in PS, for example a black to white gradient going across the screen, it seems that it is not an even blend from black to white. There is too much black, too much white, and not enough in between. Here is an example picture. The histogram display in the curves window shows what I mean. If it was an even blend, the histogram wouldn't show this curve shape. Am I correct in this? Is there a way to get an even blend?
I know this is old, but... By default, gradients are "contrasted" in Photoshop when drawing Gradients - the colors in the ends are given more presence than the midtones, to improve the visual effect (more contrasted like I said). If you want them to be evenly represented, you must go into the gradient editor and lower the "Smoothness" parameter to zero. Then draw the Gradient again, and the histogram will be "flat".
That depends a lot on the recipe you used for black and your other settings in your profile.
When you say black, that could mean many different black (#000000 or K100 or C75-M65-Y25-K80)
I'm more of a print person so I don't really do any color management in RGB and I find it easier to evaluate the results of how the colors will look like in CMYK. But if this can help to understand what's going on, I made some samples to show you different type of black to show how they react when used in a gradient.
In your graphic, your black is not really black. It's a mix of colors that looks like black. You have other colors that are distributed from the start to end of your gradient, and they multiply each others. So they will saturate the mid-tone of your gradient.
In RGB there is no true black; the "real" black is #000000. But this black is still a mix of all the red-green-blue at 100%, and a very rich black in CMYK.
I made a gradient in RGB mode using only K100 and here is the histogram. The nice curve is there.
And here are the different black, all in CMYK mode. You will notice how some fill the mid part more than others. You can also see how the RGB black is really "thick"!
And here is the channels screenshot to show how the other colors in the different black are mixed with the true black. You can see which color is saturating the middle part of the gradient.
Bottom line: If you want a nice smooth and well balanced black gradient, you should try to remove the other color saturating it in the middle, use the real black at 100% and find what you prefer. It's probably easier using the CMYK color values even if you're in RGB mode.
Extra note on gradient with black for printing:
If you use a black with gradient for printing, be careful to add some of the other color too, otherwise you will see some "steps" between each shade of black as if the gradient was very low resolution! Same will happen if you do a light gray gradient when printing in Pantone or one color only. In that case, you shouldn't even make a long gradient; if you have a gray at 30% black to 0% on a 10" sheet for example, the gradient will be visibly split into 30 slices of gray of 0.3" each! Horrible result!
It's also good to add on your gradient some noise (2.0) and then gaussian blur (0.5) to get a nice smooth gradient and hide the "steps".
It's more even than it may seem at first. I took a copy of your image and cropped it to the gradient. Then I copied that gradient to a new layer, inverted it, and rotated it 180º. Then I masked half of it to reveal a side-by-side comparison with your original. The difference is almost completely unnoticeable.
A few different things are factoring in to make a "regular" gradient look a little skewed. The human eye is better at distinguishing lighter values. Our daylight vision is far better than our low light vision, for example. Many monitors have built-in color enhancements that warm or cool the picture, which would affect gradients as well. There may also be icc profiles applied to the image which cause it to display in a way that is different to its literal values.