Theory

The reason why your picture appears exactly same on each screen is not because the colors in your photo are taken by your digital camera, but they are made in the output device you work with. For example, the screen of your computer or printer.

So before I start with this subject, I’d first try to explain just how the colors on your screen are created, and what modes are available to display them.

In Photoshop, we have three different modes to display our photo, RGB (1), CMYK (2) and Lab (3).

This aside, the mode in which your digital camera takes your pictures is RGB.

So you need this in Photoshop for one reason or other.

We continue.
All these modes consist of gray values. The composition of these gray levels, displays the color in our picture on the screen.

An example.
The RGB mode, which is the default mode of our digital camera, consists of four channels. Three of them are taken by our digital cameras, Red, Green and Blue and the fourth RGB is compiled by Photoshop, or rather, your screen.

To bring evidence to all this, we first open the panel “Channels”.   If you only look at the blue channel (1), you see that the colors in this channel only consist of dark gray. This is called “Shadows” (shadows).

The green channel consists of medium gray (2), which is called “Midrange” (Midtones).

And the red channel only consists of light gray (3), which called the ‘Highlights’ (Highlights).

Looking at the composition of these three channels (4) we see, you guessed it, the color.

This is explained in a very simple manner, but in fact there is nothing more than that.

Knowing this, the conclusion is doubtful. Set the grayscale for the photo correctly, and you have a perfect view of your photo.

Bit depth / Color Depth

The Bit depth, also known as color depth, the unit of measurement for the amount of colors a pixel can display. For example, a pixel in an 8-bit image has the ability to display 256 shades for each channel.  Where’d you get 256 shades?
A black / white photograph, or to put it in Photoshop words, is a bitmap that has a bit depth of 1, the pixel is either black or white. One of the two.
In short, a picture with a bit depth of 1 has 1 X 2 = 2 shades. So 2 gray levels, white or black.  And a photo with a bit depth of 8 has 2 X 2 X 2 X 2 X 2 X 2 X 2 X 2 = 256.   So 256 gray levels per channel.

Each gray value is displayed with a number. So Black has the value 0, and white the value 255.

So you see that the pixel in the image below, where I move on with the pipette (1), has a value of 84 in the red channel, value of 69 in the green channel, and 62 in the blue channel (2). This is so obvious when you only show the red channel (3).

When we know that each channel has 256 different color values, it is easy to calculate how many colors our picture has. 256 X 256 X 256 = 16,777,216 colors.

If you have an RGB image with three channels, then you have a photo with a bit depth of 24.

In a CMYK images, we have four channels, so a bit depth of 32.

This is all just theory, the only thing you should remember is that by adjusting the grayscale, we can change the colors in a photograph. And the lower the gray value, the darker the color becomes.

RGB, CMYK or Lab

Simplest is always RGB.

Why? One because, your photos from your digital camera are taken in RGB, two, because it is easier to work with three channels

instead of four channels, and three because you can work correctly with RGB than CMYK.

If you are sending your photos to a professional printer and they explicitly request you to do so, change the setting from RGB to CMYK.  But otherwise, keep it in RGB.

You can perhaps use Lab to sharpen or blur your photographs or adjust the contrast or brightness, so that you can touch the colors in your picture.

But unless you are a professional, it’s best and easiest to work in RGB.

To change the mode of your photo, click the “Image” in the menu bar, choose “Mode” in the drop-down menu, and make a choice.

You can change the mode of your photo at any time. This does nothing to the display of your photo.

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