Unit 30 – D2 – Impacts of compression and file format on size

I have saved the same digital image in three different file types, JPEG, GIF and BMP and because I did this, I am able to see the impact that is made on a file when the same image is saved in different formats. Since I have saved the image as different file formats, the size of the file has had an impact.

A Bitmap file format is used for storing digital images and is an image which is made up of millions of pixels, which are tiny dots and the bitmap remembers how the pixels are arranged in the image. Due to the Bitmap image saving the information on each pixel, the Bitmap is usually a big save file, and so need more of room on the hard drive to be saved than a JPEG, which is seen above in the screen shot. The Bitmap image is 17,498 KB which is over 14 times bigger than the original JPEG file, even though it is the same image. Also, the more the bitmap image is enlarged, the worse the quality gets and the image looks jagged. This is pixilation and is when you can see the individual pixels more than you could at the smaller bitmap file.

A GIF (graphics interchange format) is the file format that many of the images on the internet are as GIFs are relatively small (bigger than the JPEG by just over 3 times as much), so the GIF image doesn’t need a lot of space to be stored or a lot of time to be uploaded to webpages, as well as a GIF file being compatible and supported by the internet. GIFs that are found on websites are able to be a short animation, which is eye-catching. But GIFs have two colour settings, RGB or greyscale, where RGB is red green and blue mixed together to create other colours and greyscale is the shades of grey from black to white, so solid colour areas are the best the GIF image can produce, meaning the quality of the image isn’t the best. Since the GIF has the greyscale and RGB colour scales being the range of colours that the image has, and not much colour information is able to be stored by a GIF, the file size is smaller than some other file formats.

A JPEG (Joint Photographic Experts Group) is a file that is used online a lot as a JPEG has a small file size, with good quality and the JPEG being compatible. The quality of a JPEG is good as it supports greyscale, RGB and CMYK (cyan, magenta, yellow and key which is black), so a JPEG has more colour options and this makes the image quality better, since other file formats lacking the support of CMYK. JPEGs are small in file size, but this doesn’t affect the quality of the image and a JPEG is able to be opened in the majority of image software to view or edit due to the JPEG being used so often. In most cases, a JPEG is larger than a GIF, due to wider range of colours that have been used in the image, but it is smaller than a bitmap as not store every single pixel and the associated information.

I have saved the same digital image with three different file resolutions, seen by the screenshot above. One of the files is where it was half the original size, one is a quarter the original size and the other is larger than the original size. Since I have saved the image as different resolutions, the size of the file has had an impact as the larger the resolution is, the more pixels there are in the image and more data is saved. The original image had a resolution of 5184 x 3456 and had a size of 1,242 KB. I then reduced the resolution to exactly half of the original resolution, 2592 x 1728, and had a file size of 371 KB, which is over 3 times smaller the original file size, due to the amount of pixels in the image dropping. I then changed the resolution to 2994 x 2494 and since this was a slightly bigger resolution than my first change, it had a larger file size, of 529 KB, as there were more pixels in the new image. I finally changed the images resolution to 5988 x 4998. This was larger than the original image, and had the largest file size of the image as it has the most pixel information to save. So, the larger the resolution of your image, the more pixels it will have to make the image, so the file size will be increased as more information is stored about the image. A high quality image will generally need a larger save file and the smaller file size the lower the quality of the image is.

I have changed the colour depth of the original image 3 times, to colour depth 8-bit, colour depth 128-bit and colour depth 256-bit. The lower the colour depth, the less colours are in the image and as there is less colours in the image, there is less information to be saved and the lower the file size is. I first changed the colour depth to 8-bit, meaning there are 8 colours in the image. This is one of the lowest colour depths you can have in fireworks and due to the original image using more colours than the 8-bit image, the new image had a lower file size. Then I created a 128-bit image, which is the second highest colour depth in fireworks and the file size increased from the original of 1.21 MB to 1.68 MB. This means that the 128-bit image had more information to save than the original image did, meaning it needed more room to be saved. I finally saved the image as a 256-bit, which is the largest colour depth you can have in fireworks. This caused the file size to increase by nearly 1MB of the original image, where the original image was 1.21 MB and the new image was 2.11 MB, meaning that there was a lot more information in the 256-bit image than the original image. The lower the colour depth, means a lower amount of colours possibly used in an image and the lower the colour depth is, generally the lower the image quality is and the smaller the file size is, but the higher the colour depth is, the more colours can be used meaning the quality of the image should be higher. But in some cases, the amount of colours in the image doesn’t match the colour depth, so the colour depth isn’t always needed to be on the highest option.