[sdiy] GR-500 schematics

[Samppa Tolvanen]

On 7/25/06, Andre Majorel <aym-htnys at teaser.fr> wrote:
>
> To anyone with scans to publish :
>
> the average 300 DPI black and white schematic page can be
> compressed to 50 kB (100 kB at 600 DPI).
>
> The secret is to reduce the scan to black and white (as opposed to
> greyscale). Once that is done, a scan of a typical text or line
> art document becomes very redundant and lossless compression
> algorithms can be used. I use TIFF with the Group 4 compression
> method. It yields compression ratios on the order of 100.
>

Hmm, I have become a great fan of PDF since the storage medium sizes
alloved me to carry it home. I guess for free printer driver type
solutions it still allows lossless LZW compression, right. (And JPG
too).

On many large TIFF or JPG prints (which look fine on the screen) B/W
laser printer needs adjustment on the picture brightness/contrast to
make good enough results while printing, no matter what the dither
adjustment is, midtones on a grayscale pics mess up the picture.

> If you use black and white, you have to use a very high
> resolution (>= 300 DPI).
>
> For low resolutions, it's best to stay in greyscale. Either use a
> lossy compression (JPEG) or posterise to as few grey levels as you
> can get away with (usually 5 to 10) and use a lossless compressed
> format such as PNG. Try both and see what bothers you more : low
> intensity resolution (posterised PNG) or artefacts (JPEG). I find
> that artefacts hurt readability more than posterisation does so I
> usually avoid JPEG for this application.
>
> In my experience, a 300 DPI TIFF/G4 file and the same scaled down
> to 100 DPI and posterised to 8 levels are roughly equivalent in
> size.
>
> If you save as JPEG and find yourself lowering the quality factor
> because the file is too big, stop and think about what you're
> doing. For highly redundant images like text and line art, JPEG
> rarely provides the highest quality/size ratio.
>

Thanks for the tips! For clearly B/W documents I'd aim at highest
possible resolution with the least amount of "colors" or grayscales
for best printing.

Samppa