Posts Tagged ‘image editing’

The four most common image file formats are: TIF, JPG, GIF, and PNG. Programs like Photoshop and Elements support each of these formats.

These are not the only options just the most accepted. A web page requires a jpg, gif, or png because those are the file types that a browser can read.

TIF supports most color spaces and the file format contains many options such as the option to add tags to each image- but the biggest benefit is that a TIF file can be exchanged among platforms with no problem.

When saving a TIF file you can use the LZW lossless compression as an option. Lossless compression simply means that there is no loss of quality from compression. That means that you can always read back exactly what you thought you saved. Bit for bit with no data corruption. TIF files are generally very large. But the size is not a disadvantage because it just means there is a lot of detail saved within the file. A TIF should be used when high quality and archiving are a major consideration.

There may be times when quality is less a consideration than file size such as web pages or email- in this case choose a jpg.

JPG uses lossy compression which means that there is loss to image quality. But JPG was designed to be lossy to allow for major size reduction in the image. So when we open a JPG file the data expands so that we may view it and it is not exactly as it was before. This is loss of quality, purity and integrity. And it is unrecoverable. So depending on your image you need a good reason to use a JPG since its purpose is to create a smaller file. A good reason would be email or for the web.

Photoshop and other image editing programs will allow you to choose a quality setting when saving a JPG. Always use the highest setting.

When using JPGs you must also realize that each time the image is opened and then saved again it further compresses creating more data corruption. Each time it is rotated or added to- it is further compressed and more data is lost. Opening and viewing the JPG file is no problem. But every time you perform a save operation more data is lost. You can begin to see that this compression is leaving artifacts (or blurry spots) in your image over time by zooming in by 300% and the data loss becomes apparent. Over time these corruptions will become apparent when viewing the image at regular size.

So rather than continuing to edit and save a JPG file you should just begin with an archived Master TIF file and begin anew.

When using a camera that uses JPG files you should immediately save the image as a TIF and keep that as your master as you can then feel comfortable that there will be no quality or data loss with in the file. From the TIF file you can create JPG copies if needed. Keep in mind that you will not gain quality by transferring your JPG images that you already have to TIF format. But you can feel secure that you will not lose anymore quality. So if your JPGs already contain data corruption they will keep these if transferring to a TIF format. Which is why saving to a TIF to keep as a master copy that you will never rewrite is the first thing you should do if your camera does not support TIF files. Save any new changes to a different file. Never rewrite over your master copy.

The small JPG file size is great but it comes with a price.

GIF has no real value in photo quality images and is best suited for the web. JPG is a much better choice for the web for both quality and file size. However if your image has any transparency then use a GIF or PNG file as JPG does not support this. PNG will produce the better quality image but GIF is still the better choice as Internet Explorer does not always read the transparency information in a PNG file as other browsers do. So although I don’t feel that GIF is the better choice for quality it is the better choice for browser compatibility.

PNG supports lossless compression and is well suited for master copy like TIF files. It will also create a smaller file size than TIF. But TIF is the undisputed leader for image quality. When nothing less than maximum quality is required than always choose a TIF file to save your images. TIF is also the most common file asked for by commercial printers.

Image resolution is very important when using any sort of digital imaging program. It is what decides the print dimensions and quality of your image.

Printed dimensions and quality are measured by dots per inch (dpi). 300 dpi will produce high quality for any size image. Once printed it is referred to as ppi or Pixels per inch.

Many home printers can produce quality images at 150dpi but most companies will ask for a 300dpi image.

Printing is done using four inks, Cyan, Magenta, Yellow and Black. There are four separate dot patterns for each color. Dots per inch refers to the number of dots in a square inch.

At 300 dpi all of the dots in each square inch are next to each other with no space between them. An image at 150 dpi has 150 dots per square inch. With that in mind you can begin to see how a lower resolution produces a lower quality or how an increased image size becomes a lesser quality image.

Suppose you took a 300 dpi image at 4in. x 4in. and increased the size to 8in. x 8in. You only have the beginning 300 dpi per inch at the original size. That means that you have taken those dots per inch and stretched them to cover the 8 x 8 area and have significantly lowered the dpi of the image to 150dpi. Because of this it is better to decrease size than increase- as decreasing an image size will actually increase dpi, as I said before you have the original 300dpi to work with. So basically changing an image size changes the dpi. So if you decreased a 300dpi 4in x 4in image to 2in. x 2in. you have just changed the image to 600dpi because those dots have just moved closer together rather than farther apart as I the first example.

But…

Printing at higher than 300 dpi will just take longer to print as the dots begin to overlap and it is only needed for the dots to be next to each other. Unless you are planning to upsize an image there is no need to go higher than 300dpi.

Photoshop has a great image resize feature and will allow you to adjust or add dpi so that upsizing an image will retain quality. There are also a variety of Photoshop add ons that will help with this.

Some printers will tell you that all they need is 200dpi. Other times newspapers or magazines may go as low as 100 or 85 dpi. Lowering dpi for images is safe as you are simply eliminating dots that already exist. But raising dpi can be dicey as Photoshop or add ons will need to add dots per inch to give you the desired dpi. If the upsizing is not drastic Photoshop does a pretty good job. But if you need to significantly increase the dpi and size than ultimately image quality is still lost even though you still have a 300dpi image because Photoshop is taking the information in the image and simply doing the best that it can in deciding which dots to add. And as good as that may be, it will never be as high quality an image as if those dots came from the actual image rather than placed there by Photoshop.

300dpi will produce a higher file size but because of everything mentioned, if file size is not a factor than you are better off having the largest size image at 300 dpi and sizing down as needed.