Adobe Photoshop

Common File Formats

JPG or JPEGs

JPEGs are probably the most commonly used file format. It is the mp3 format of pictures so to speak. JPEGs allow you to save memory by creating highly compressed images that take up as much as only 1/10 of the space taken by TIFFs and GIMPs. Now why would that be a bad thing, you might ask. Saving space is always good right? However, the flip side to compression is the loss in quality of the images. JPEG allows great compression by compromising on the quality of the image. However, this compromise is worth it in many cases. These include casual photography, posting pictures on a website and sending images as e-mail attachments. Another point to note is that JPEG images suffer from “generational compression.” This basically means that every time you edit and save a JPEG image, the JPEG engine compresses the image some more so you lose further detail and quality. It is for this reason that experts recommend you create a new JPEG file from a RAW or TIFF image every time you wish to edit something. JPEGs perform lossy compression on images, which means that you lose the original information from the image every time you make edits and save it. The degree of compression can be selected, such that medium or moderate levels of compression can leave you with highly detailed images that are just as good as TIFFs or PNGs for most purposes. Another factor that works in JPEGs favor is that it is a highly compatible file format that can be opened and edited in any operating system (MAc/Windows/Linux).

TIFF

These are the workhorse formats of professionals who work in the image editing field (designers/photographers). It is a very versatile format that is both flexible and widely compatible. In general practice, TIFF is used mostly as a “lossless” image format and so is large in size. TIFF preserves all of the detail and information in images. This has an impact on file size considerations for example a standard 800*600 JPEG image might be 200Kb but the same image in TIFF might run upwards of 1 MB.

PNG

These are similar to TIFFs in that it is also a lossless format. However, PNG file sizes are generally slightly smaller since it performs some compression on images. However, this compression is reversible so information is not lost. These are used frequently for the web as it retains the transparent background, though the GIF file format will have a more appropriate web size.

PSD

This is the proprietary image format used only by Photoshop. When you perform extensive image editing on Photoshop, with different layers and effects applied, the PSD format saves all these changes such that you can continue working with these edits later on. Due to it’s proprietary nature, PSD files can only be opened by Photoshop and not by any other program. Furthermore, PSD files are usually very large since they preserve all the different layers and the edits you have made on them. It is not unusual for PSD files to exceed 50 Mb! PSDs are very similar to iMovie projects in that they both preserve the editing power of the formats and both are very large files (or rather a collection of files) in general. Images are saved as PSDs while editing them on Photoshop and then TIFF or JPEG versions of the final edited image are created for normal use. (slideshows/website/attachments). I myself usually keep a PSD file along with the other file formats such as JPG, PNG, GIF, PDF, etc.

What You Might Use Each Image Format For

JPG:

• Uploading images to a website or blog
• Sending images as attachments via email
• Casual photography
• To save space on your computer

PNG/TIFF

• Need maximum details
• Enthusiast photography
• Scanning purposes

PSDs

• Almost exclusively for extensive editing in Photoshop
• To maintain your UNDO history and image layers

Follow these links for complete software compatibility lists.

"Popular Image Formats (Photoshop)" by STA Program at Trinity College is licensed under CC BY NC SA 3.0

Resizing and Cropping Images

Most of the time when working with pictures it is very important to know how to modify the dimensions of the picture or how to create a new picture using a smaller part of a picture.

Changing the dimensions of an image

Suppose you have a 1024 by 768 pixels image and you want to shrink the whole image down to, let’s say, 800 by 600 pixels.

All you have to do is open the picture with Photoshop and then do the following:

1. Go to the Image menu and select Image Size

2. The Image Size menu is going to open. If you want your picture to be scaled by constraining the proportions of the image (keeping the same ratio of the height to the width of the image) then check Constrain Proportions and then type the new width and the new height of the picture. Note that by checking the Constrain Proportions you can type in just the width of the picture and the height will automatically show up. If the Constrain Proportions would not be checked, the user would have the possibility of choosing whatever width and height for the new image having the risk of loosing its proportionality.

3. Hit Ok to make the changes.

4. In case the picture does not have the right size you can undo the modification by hitting Ctrl+Z on Windows or Command+Z on the MAC.

5. When the picture is the right size you can save a new copy of the picture by going to File and clicking on Save As. Name your picture, select the type of file your picture is going to be saved as and hit Save.

Cropping an image

Sometimes you may want to create a new picture just by using a small portion of the original picture. In this case all you have to do is use the Crop tool in Photoshop. Here is what you should do:

1. Open the desired picture in Photoshop.

2. Select the Crop Tool from the Tools palette.

3. Using the Crop Tool drag a rectangular region on the picture to indicate which part of the image you want to crop to. Remember that what lies outside the bounding rectangle is not going to be part of the new picture. You can always move the region around by clicking inside that region and then move it around.

4. Once you are satisfied you can double click inside the bounding region to crop the picture.

5. Save a new copy of the picture by going to File and clicking on Save As. Name your picture, select the type of file your picture is going to be saved as and hit Save.

"Photoshop tip#1: Resizing and cropping images" by STA Program at Trinity College is licensed under CC BY NC SA 3.0