Lesson 3 and Lesson 4

3. Image Size and Resolution

In this lesson, I am introduced to the basic building units of a raster graphic, the pixels. Pixels is the square unit of color. An image size is determined by the number of pixels in an image while the resolution of an image is determined by the number of pixels that are packed in a square inch when you print that image. It interesting to know that the resolution value applies to print only and it's actually meaningless on screen.I find out that "dpi" actually stands for "dots per inch ", a measurement of how much detailed color information a raster image contains.

I understand how image size is calculated and before this I actually did not know that to calculate an image size one have to take into account the RGB pixels. For printing, the image should at least have 300 dpi (CMYK) which is an industry standard for fine resolution images while for the web, 72 dpi (RGB) is enough. I can change the resolution value of an image by upsampling or downsampling it. However, if I do not want to change the number of pixels but only the resolution value I can turn off the resample image check box. However, at such I will change the width and height value of the image.When resampling an image, there will be interpolation whereby Photoshop rewrites every single pixel in the image. Thus, both upsampling and downsampling is technically a destructive modification. 

There are 6 interpolation settings. They are the nearest neighbour, bilinear, bicubic, bicubic smoother, bicubic sharper and preserve details respectively. The automatic setting when downsampling is the same as bicubic sharper while when upsampling, the automatic setting is the same as preserve details. After this lesson, I understand how to change the interpolation setting to the one that is the best to preserve the quality of an image when resampling an image.

4. Crop and Straighten

This lesson is pretty straightforward and easy. I know how to crop and straighten the image already. The lesson recommended us to use the ruler tool when straightening an image so that we can modify the line as much as we want before straightening. At such, the image will be straightened more accurately. I learned that when I rotate the image as I crop it, I will actually resample the image. I have not come across the perspective crop tool before hence it's vital to learn how it works.  I am amazed by the content-aware crop which can help to fill in missing background details while cropping an image.