Jumat, 23 September 2011

Photoshop Tip: Description of File Formats and When to Use Them

Adobe Photoshop is the most used software in art licensing for manipulating and creating art. It uses a native format of PSD but allows a person to save files in other formats such as JPEG, PNG, TIFF, PDF, EPS.

Before saving a file to another format, it should ALWAYS be saved in Photoshop's native format (at 300 dpi or more) to preserve all Photoshop features such as layers. That way the artist can do future editing of the images and text contained in the layers. The other formats will be used for other purposes such as submitting low resolution art (72 dpi) to manufacturers for possible licensing, submitting art in formats requested by manufacturers, and placing art on websites. This article describes the pros and cons of these alternative formats and when to use them.

JPEG Format
The most used format to transfer art in the licensing industry is JPEG (Joint Photographic Experts Group). It was created in 1992 to compress files to make them smaller in size and faster to download and open. The degree of compression can be adjusted to allow a tradeoff between storage size and image quality. JPEG files can be read by most software and has the filename extension of .jpg.

• Pros
- Significantly compresses the file size.
- Saves an image in CMYK, RGB, and grayscale mode. To find out the difference between CMYK and RGB, read "Photoshop Tip: When to Use RGB and CMYK Color Gamut."
- Saves an image as one or more JPEG using the Save For Web & Devices command.
- Can save as a progressive download which loads faster and saves space. This way, after a smaller part of the whole file has been received, the viewer sees a lower quality version of the final picture. The quality then improves progressively through downloading more data bits from the source.
- Has widespread usage.
- Most software supports it.

• Cons
- Uses lossy data compression of the file size by selectively discarding data. It degrades the resolution of the image EACH time the file is saved. Note: Theoretically lossless data compression (no loss of data) is possible with a JPEG file but must be built into the software. Photoshop does not give that option.
- Automatically adds a white background if it was transparent.
- Merges all layers into one layer.
- Supports only 8-bit images.* If a larger bit image is saved as a JPEG, Photoshop automatically lowers the bit depth to 8.
- Some software applications may not be able to read a CMYK file saved in JPEG format.

• Uses
- Send low resolution art to manufacturers via e-mail for licensing consideration.
- Send high resolution graphics to trade publications via e-mail for paid advertising. Because the file is compressed significantly, the size of the file is small enough to download faster than other formats. Note: I have experienced good results (color and resolution) when sending a 300 dpi RGB JPEG file (with my own embedded color profile and at the size it will be printed) via e-mail to Total Art Licensing and Art Buyer publications.
- Can be used for low resolution art on websites and blogs.
- Can be used to reduce the file size to increase file transfer speed on the internet.
- Can be used to reduce the file size to increase the speed when printing marketing and other materials on home printers.
- Send a high resolution file to a manufacturer once a licensing contract is signed. Select the baseline optimized to optimize the color and have a slightly better compression.

*8-bit images means that each pixel in an image (the dot that makes up the smallest part of an image) can represent 256 different states (2 to the 8th power) or over 16 million color shades in the RGB color system (256 times 256 times 256). Until recently most monitors, inkjet printers, and other devices could only show 8-bit images. 8-bit images are also called 24-bit images (3 times 8). Now scanners and digital cameras are capable of producing higher bit images such as 36-bit and 48-bit (billions of colors). These higher bit images may be used in high quality digital photographic work but is not used for licensed art on products. The printing devices does not support that many colors. Thus, 8-bit images is the norm used in art licensing. Note: Some printing devices support MUCH less colors than available for 8-bit images.

JPEG 2000 Format
JPEG 2000 was created by the Joint Photographic Experts Group in 2000 with a filename extension of .jp2 or .jpf to enhance the original JPEG capabilities. It supports all JPEG capabilities plus more.

• Pro
- Supports everything that JPEG does.
- Provides both lossless (no loss of data when compressed) and lossy compression.
- Saves an image in CMYK, RGB, and grayscale mode.
- Artifacts in file compression is less visible. There is almost no "jaggies" around the edges of the image.
- It supports transparency in images.
- It supports higher bit depths.

• Cons
- Merges all layers into one layer.
- Does not have widespread usage.
- Not widely supported by all web browsers especially the older ones.
- Not supported by all graphic software.

• Uses
- See JPEG format uses.
- Can be used to save icons and images with transparent backgrounds. They can thus be easily incorporated into other pieces of art and patterns without having to remove the background.

Caution: It is better to use the original JPEG format instead of JPEG 2000 unless it is requested by a manufacturer. It is not recognized by all software and the file may not open.

PNG Format
PNG (Portable Network Graphics) format is used for lossless file compression with a file extension of .png. It compresses a file without losing bits of data unlike JPEG formatted files. PNG was designed for transferring images on the Internet and not for professional-quality print graphics.

• Pros
- Supports lossless compression.
- Can save 24-bit images.
- Supports RGB, Indexed Color, Grayscale, and Bitmap mode images without alpha channels.
- Preserves transparency in grayscale and RGB images.

• Cons
- Not ALL web browsers can read PNG images, although the later generation browsers do.
- Does not support CMYK images.
- Merges all layers into one layer.

• Uses
- Can be used to save icons and images with transparent backgrounds. Images without backgrounds saved as PNG files can be easily incorporated into other art and pattern files without having to remove the backgrounds.
- Can be used to display high color images (greater than 8-bit).

TIFF Format
TIFF (Tagged Image File Format) file format was originally created by Aldus for use as desktop publishing for image-manipulation, publishing, and page layout applications with a file extension of .tif. It was acquired by Adobe Systems in 2009.
• Pros

- Can compressed the file either as lossy (JPEG) or lossless (LZW and ZIP)
- Saves an image in CMYK, RGB, and grayscale mode.
- Can handle images and data within a single file, by including the header tags (size, definition, image-data arrangement).
- Supported by virtually all paint, image-editing, and page-layout applications.
- Supports layers.
- Can save 32 bit images.
- Preserves transparency in images.

• Cons
- Creates larger files when no compression is used and also if the file includes many layers. Thus, it takes a long time to download and uses a lot of disk space.
- If an application cannot read the layer data, it opens the file without layers.
- Not supported by web browsers.
- Has not been updated since 1992 and thus lacks advanced imaging features.

• Uses
- Scan images in TIFF format without compression selected. The details of the image will be maximized but scanning the image may take a long time, have a large file size, and take a long time to download.
- Take digital photos with TIFF format (if camera supports it) for a better quality photos than JPEG. However, the files are huge, less photos can be stored on the memory chip, and results in a longer wait time between taking photos so that the data can be transferred to the memory chip. The quality may not be noticeably better than JPEG. Note: Many digital cameras can save files in RAW format which is the best quality photos. RAW format is supported and editable in later versions of Photoshop. However, RAW format is a proprietary format for each camera manufacturer and may not be readable by software in future years. Thus, RAW formatted files should be converted to TIFF or JPEG for archival storage.
- Manufacturers may request a layered TIFF file so that they can manipulate the image to their own specifications. Of course, this file will only be sent after a licensing contract has been signed.

PDF Format
PDF (Portable Document Format) was created in 1993 by Adobe Systems for document exchange and is the de facto standard for printable documents on the web with a filename extension of .pdf. Depending on the settings chosen, compression and downsampling can significantly reduce the size of a PDF file with little or no loss of detail and precision.

• Pros
- Offers lossy (JPEG) or lossless (downsampling compression) compression of files
- Gives multiple choices in compression and ways pixels are deleted.
- Preserves Photoshop layers.
- Supported in most graphic (vector and raster) and page layout applications.
- Preserves transparency in images.

• Cons
- PDF Format in Photoshop only allows one image to be saved per PDF file. If multiple images need to be saved in one PDF file, use Adobe Acrobat software.

Note:  Artist Laura Freeman pointed out that you CAN save a multi-page PDF file in older versions of Photoshop.  Read how to do it in the 4th comment to this article. And read comment #5 on how to create a multi-image PDF file in Photoshop versions CS4 and CS5.

• Uses
- Manufacturers may request a layered PDF formatted file if they do not own Photoshop but have other software that will read layered PDF files.
- Many artists use Acrobat software (PDF) to send multiple images as one file to manufacturers for licensing consideration. Note: If you use a PDF file with multiple images, make sure that the file is compressed and not too large or the receiver may not be able to open it with their e-mail reader. Many readers limit the file size that is attached to an e-mail. An alternative is to put the PDF file on a CD and post it (mail) to the manufacturer.

EPS Format
Photoshop EPS Format (Encapsulated PostScript) language file format has a file extension of .eps. EPS format was created for vector generated graphics in Adobe Illustrator but does support bit mapped (raster) graphics. For more information, read "What is the Difference between Photoshop and Illustrator?"

• Pros
- EPS format supports Lab, CMYK, RGB, Indexed Color, Duotone, Grayscale, and Bitmap color modes.
- Can save color separations of CMYK images.
- Can contain both vector and bitmap graphics.
- Is supported by virtually all graphics, illustration, and pay-layout software.

• Cons
- When a EPS file containing vector graphics is opened in Photoshop, it rasterizes the image, converting the vector graphics to pixels unless it is downloaded as a Smart Object. Smart Objects preserve an image's source content with all its original characteristics, enabling you to perform nondestructive editing to the layer.
- Merges all layers into one layer.

• Uses
- Transfer PostScript artwork between Photoshop and other software such as Adobe Illustrator.
- Send a high resolution EPS file to a manufacturer if it is requested and once a licensing contract is signed. Note: This is NOT an usual request so make sure that the manufacturer understands that the art was generated in Photoshop as a bit mapped image (raster) and is not a vector image. As a raster image, the resolution will degrade if the file enlarged too much while a vector image does not degrade when enlarged.

File Format Sizes
The size of the file is dependent on whether the file is compressed, the type of compression, and the number of layers in the file. Below is a table comparing the different formats when converting a Photoshop RGB 12 inch square image at 72 dpi. Notice that a maximum quality JPEG file with one layer is only 972KB in size while a TIFF file with 55 layers and compressed as a ZIP file is 5.1MB. Not shown in the table: The same file at 300dpi JPEG (maximum quality) is 4.9MB while a 300 dpi TIFF file with 55 layers and ZIP compression is 133.6MB. The same file with no compression is 146.1MB in size.

Note:  I used an example of a 55 layer file to compare the sizes of the various formats but Photoshop supports a maximum of 8000 layers.  However, if that many layers are used, the file size could become larger than the maximum file size supported by Photoshops PSD format which is 4GB for the CS5 version and 2GB for lower versions of Photoshop and other software.  The maximum TIFF file size is 4GB (most applications cannot open a TIFF larger than 2GB) and PDF is 10GB.  Hint:  If you wish to save a Photoshop CS5 file larger than 4GB then save it in a PSB format.  PSB is a large format PSD file with a maximum size of 4 million TB.  However, you better have a computer with a fast processor and lots of memory to open that large of a file or it could take a L  O  N  G time to open and save.  :)

The most used format for showing art on websites and blogs and submitting low resolution art to manufacturers is JPEG. Although, using PNG files is becoming more prevalent for showing art on websites and blogs. I usually submit art to manufacturers at 72 dpi in RBG at a medium quality JPEG file. I have found that a high resolution (300 dpi) JPEG file of the final art is usually the most requested format by manufacturers. Of course, it is sent to the manufacturer AFTER the licensing contract is signed.

Some artists and agents send multiple images in a Adobe Acrobat PDF file (either by e-mail or CD via "snail" mail) to manufacturers for licensing consideration. Saving PNG files of individual images and icons without backgrounds is a good practice because PNG is lossless and supports transparent backgrounds. TIFF files are readable by all graphic software, is lossless, and supports layers but the file size can be huge and take a long time to upload.

If you would like to share information on how you use the different formats or any comment about this article, please enter them in the comment section below.
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