scanning photos

[woodyracing]

ok so the negatives have a graining (the higher the ISO the more grainy) and the photo paper also has graining.

So assuming I scan a photo at say 300dpi, which would give the best results, a larger print photo say 8x6 or a standard size photo say 6x4 ?

[paul-collins]

300 dpi from what? The negative? (hopefully not) A standard 4x6?

[woodyracing]

sorry, i mean if i scan the photos at 300dpi
obviosly a larger photo would give a larger scanned image but if they were both resized to say 1600x.... then which should be the best quality ?
a scan from a smaller photo, or a scan from a larger photo.

[KC]

The less resizing the better the image, so the larger the original (assuming its a good picture to start with) the better the enlargement. There is some software out there than can help to interpolate images and clean them up slightly but it will still not replace a good large image to begin with.

[woodyracing]

the scanned images come out far larger than i need, and software is very good at reduction. I use Paint Shop Pro 7 (full commercial version) which i find is very good.

[paul-collins]

What KC says makes sense to me - the grain on the negative is pretty fixed as far as having an influence on your scan, but the grain from the print is a fixed density based on the paper - which is to say, an 8x12 will have 4x the dots for a region in the photo that a 4x6 will have.

Now, granted, since you're resizing anyway, the improvement may be marginal - but it's still going to exist. Always best to get the size right in the scanning, too, rather than resizing after the fact (unless your resize is dividing the size by an integer, so there's as little interpolation as possible).

[woodyracing]

the way i work currently is to scan at a higher dpi than i need and then reduce the image in software. I think reduction works better than enlargement (interpolation).

[Les]

are you saying then to only resize if it is to go 1/2 size or a third or quarter? Never thought of that.

I have a question - my digital camera software says I can save as a jpeg in high, standard or low quality but the resolution for all 3 files is the same. how come?

[KC]

The image size does not change, but the level of sampling does. A larger file contains more data to use in contingency if the original data fails or fails to hold the details you were trying to capture. An uncompressed .tiff image can be up to 10 times larger than a compressed .jpeg image. When the image is regenerated by the computer there is more to draw from and finer detail can be had because the image has more data to work with.

A 2.1 mpixel .tiff image from my Olympus is more than 15 mbytes of data. It would make the most sense to shoot only in .tiff for the best images, but the files are so huge they eat up memory and can take quite a while to save to disk.

[paul-collins]

Originally posted by Les
are you saying then to only resize if it is to go 1/2 size or a third or quarter? Never thought of that.

I have a question - my digital camera software says I can save as a jpeg in high, standard or low quality but the resolution for all 3 files is the same. how come?

I'm saying that the computer has an easier time figuring out what to drop if the ratio is a simple fraction. This matters for the cheaper software solutions you might use; it may not for Photoshop or other high-quality stuff.

About your jpegs - the quality is referring to the compression used in the photo. High quality means preserving more direct pixels, and interpolating fewer of them in between the direct ones. Low quality reduces the number of direct ones, and interpolates more. The image files are smaller for lower quality, but take a little longer for the graphics card to figure out how to display.

A bitmap (.bmp) has no interpolation - every pixel is stored exactly as found in the original image.

[Les]

thanks for the explanation

[Aysedasi]

Originally posted by woodyracing
the way i work currently is to scan at a higher dpi than i need and then reduce the image in software. I think reduction works better than enlargement (interpolation).

I've been doing the same for some time. But I normally scan at 600 dpi. I use Photoshop for my editing.

[andy_b]

same here, I find that this helps if you want to crop or manipulate or modify the image as well as you can do this before you reduce to your desired size, reducing any dogey edges which you might have created (eg: making the background darker).

Personally I use Photoshop