How to specify the desired size of an image.

We need to know what size image do You need. If possible, specify the size in pixels.

  • The most exact and simple way is if You provide us with the desired pixel count. [e.g. "I need an image with at least 1200 x 1600 pixels", and so on]

  • Resolution specifies the size of an image only in conjunction with the printing size and the dpi/ppi ratio of Your printer (see below).

  • Therefore, specify the size in pixels, resolution alone does not tell us anything about the pixel count You need.

  • How can I find out how many pixels will I need? See below.

We also need to know which image format do You need. The most requested format is 100% jpg

  • The scans are in TIF, 16bits/channel. This is a lossless format, but it has a huge file size. Experts can appreciate the advantages of tif, but it has too large files for normal use. The big size scan has about 140MB in tif.

  • More practical format is jpg. It is lossy, but 100% jpg looks very similar to tif. The file size is about 8 times smaller, so it is easier to email/ftp scan that has been converted into 100% jpg. We will gladly convert tif to jpg for You. The big size scan has about 18MB in 100% jpg..

  • What does that 100% mean? Jpg format has adjustable compression. Jpg 100% is the highest quality. It is almost impossible to notice any loss of quality against TIF. It should satisfy even the most demanding user. Even 80% jpg is OK (that has even much smaller file size). Lower than 80% quality jpg is still OK for viewing, but not recommended for printing.

  • I have prepared a special page where different formats are compared.

  • There are more modern formats that jpg.  They offer even better quality and smaller size than jpg. Not every graphical program can read them though, so check Your software first. Examples include lwf, jp2. Jp2 has also lossless setting: the resulting file is 1/3 smaller than tif. We will gladly send the scans in these formats.

 

Is resolution adjustable?

Definitely. Resolution is a freely adjustable property of an image. (You can set the resolution according to Your needs in any better bitmap software, such as Photoshop).

Are there more kinds of resolution?

Yes. There is ppi and dpi. The first being "pixels per inch" and the second "dots per inch". Dpi and ppi often get confused. Ppi refers to a file and dpi refers to a printout.

Does ppi equal ppi? 

No. Ppi is often 4 times smaller than dpi.
Pixels are the smallest units of every raster (bitmap) image. If You magnify an image, You will see them as small squares of uniform color. In CMYK color space, each square has a specified amount of cyan, magenta, yellow and black color. Therefore, printer can use several dots of hue to render one pixel. For instance, it can print a blue dot and a yellow dot next to each other to form a green color. That means that dpi and ppi are correlated, but not the same.
Each type of printer uses different method and patterns to print dots, so there is no universal coeficient, but here are some simple rules: Laser printers print generally with 300 or 600 dpi resolution, and need the ppi resolution of the source file 72 or 150 ppi.
High-end, professional devices can (but hi-res is not always needed) print with 1200 dpi or more, and need source files with 200 to 300 ppi. Please check Your print shop assistant, or a manual to Your printer. Monitors are commonly set to 72 ppi.

Can you give me an example? How many pixels do I need to print a letter size picture on my laser printer?

You want to print one of our posters on a laser printer. Your printer can be set to print at higher quality, 600dpi. Therefore, You need a file with 150 ppi. The maximum paper size Your printer can print on is the Letter size (A4), 8 1/2" x 11". 8 1/2" x 150 ppi = 1275 pixels, 11 x 150 = 1650 pixels. You need a file that is 1275 x 1650 pixels big. Since the printer has to use some paper for margins, 1200 x 1600 should do. If You want to be on a safe side, order 2400 x 3200 pix - You will give Your printer a bit more than it needs, but that will not hurt anything.

The maximum size of our scans is around 4096 x 6144 pixels [depending on poster shape] at 48 bits color depth (16 bits per channel).

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