Pixels, Resolution and PPI

Let me first explain what pixels are.

A photo or a scanned image consists of millions of blocks, these blocks are called pixels.

We can set the position, color and contrast of each pixel in a photo.

The quality of your pictures is determined by the number of pixels. The more pixels, more details are displayed and the smoother the picture will be.

So when you take a picture and scan it, always choose the highest resolution in Photoshop and you can still do anything with it.

What is resolution now? Resolution is the number of pixels per inch in your photograph.

What is an inch? An inch is about 2.5cm.

So when your photo has a resolution of 72 ppi means, it means that every inch has 72 pixels.

For those who do not know what ppi stands for, it is pixels per inch and is used as a measure for the number of pixels in a row in your photo description.

When you do this calculation for inch ², this is 72 times 72 and your picture has 5184 pixels per inch ².

When you increase the image to more than 500%, the pixel grid of the image is visible. If you want to disable this temporarily, click Ctrl + H on your keyboard.

Resize

In this section we talk about the image size and how we can customize it for different purposes.
As said in the previous section, take pictures with the highest possible resolution and change it later in Photoshop.

If you have a digital camera, it will take photos at 72 ppi.  If you want to print photos on your inkjet printer, for example, then you will need to increase the ppi of the image to a minimum of 300.
Just click the “Image” in the menu bar and select “Image Size” in the drop-down menu.

The dialog “Image Size” is divided into three sections.

The first section “Pixel Dimensions” (1), gives us the number of pixels in the picture.

The second section “Document Size” (2), is only about printing the photo.

And the third section has a number of options (3).

The contents of this window may seem complicated, but all this is actually quite logical.

Example:
I have the resolution set to 300 pixels / inch and the unit of measure as inches (section 2), to make it a little easy.  When I set the paper width of 20 inches, it is quickly calculated that I have 6000 pixels across a width of 20 inches. Do you follow? 300X20 = 6000.

Same for the document height, 300 pixels / inch document height is 15 inches = 4500 pixels.

For an image of 20×15 inches I then have 6000 times 4500 pixels = 27 million pixels.

If the “Constrain Proportions” and “Resample Image” options in section 3 are selected, when I change the height or width in section 2, the rest of the options adjust automatically.

The first option “Constrain Proportions” is, with any alteration of a width or height, the ratio between the two will be retained.

The second “Resample Image”, ensures that with any alteration of the resolution, the number of pixels in the picture will be adjusted.

In other words, you increase the resolution, there are more pixels on the photo, you reduce the resolution, pixels are removed.

It is therefore important that both options are selected when changing the resolution.

When the resolution of the picture increases, which is true in this case (from 72 ppi to 300 ppi), you will see that the size (in MB) of the photo at the top of the dialog box, increased significantly (to 20.3 to 77.2).

To print the picture, this is ok, when you place it on the Internet, this is too much.

The top option “Scale Styles”, is just as important when working with “Layer Styles” in the picture. We have not seen this yet, so this is not applicable.

If the resolution of the image is changed, pixels are added or removed. To determine which method the Photoshop should use for this, we select the lower box of section 3.

Just click the downward pointing arrow and choose one of these options:

The explanation from Adobe:

Nearest Neighbor

A fast but less precise method in which the pixels in an image will be duplicated. This method is for use with illustrations containing edges that are not anti-aliased, so preserve hard edges and a smaller file. The disadvantage of this method is that it can produce jagged effects, which become visible when an image is distorted or scaled or when you perform multiple manipulations on a selection.

Bilinear

A method that adds pixels by averaging the color values of surrounding pixels. It produces medium-quality.

Bicubic

A slower but more precise method based on an examination of the values of surrounding pixels. Bicubic uses complex calculations and produces smoother tonal gradations than Nearest Neighbor or Bilinear.

Bicubic Smoother

A suitable method for enhancing images on the basis of Bicubic interpolation, but designed to produce smoother results.

Bicubic Sharper

A suitable method for reducing the size of an image based on Bicubic interpolation with enhanced sharpening. This method maintains the detail when you resample. Bicubic Sharper makes some areas of an image too sharp, try Bicubic.
Phew, I got all nervous when I started reading.

My explanation:

Nearest Neighbor

This option takes a pixel, multiplies with the degree of resolution of the picture.  So you have a photo with a dpi of 100 and change this to 300 dpi, it copies one pixel to 9 pixels. That is 3X3.

Bilinear

This option is completely useless.

Bicubic

This option is useful. It compares multiple pixels, is will add a new pixel. This is also the option that you need to use in most cases.

Bicubic Smoother

this option does the same as the previous one, this only makes the transition, after the addition of the pixels, smoother. Can you possibly use a picture when there is a lot of noise in your picture?

Bicubic Sharper

ditto the previous one, this only makes the transition between the pixels harder.
We continue in the next lesson.

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