Picture Quality ?

sparks · #1 (**permalink**) 03-12-2003, 08:01 PM

I have noticed that some of the pictures you guys send in are great. It seems the ones that I have uploaded look like sh!t. I used a picture and than scaned it . It never seems to be the correct size either? Plus it seems that the pics come out way to big?????? HELP!!!!!!!!!!

6T5 Cbra · #2 (**permalink**) 03-12-2003, 10:02 PM

Sparks,

Most of the time a scanned picture will not be as good as the original. At least that's my experience. I would venture to guess that the majority of the pictures posted on this site were taken with a digital camera. Mine were.

As far as sizing goes, you need to 'resample' or 'resize' the picture in a photo editor program (Photo Shop, Photo Paint, etc). Resample them to around '640 x 480' or '800 x 600' pixels. That allows most people to view the pictures on the screen without having to pan across to see the whole thing.

Gene

STG · #3 (**permalink**) 03-13-2003, 04:27 AM

Sparks,

The relationship between scanning resolution, digital camara resolution, computer displays, printing resolution and image size can take a little while to grasp.

Here's my attempt at explaining:

My Minolta D7 camera creates an image that has 2560 horizontal pixels and 1920 vertical ones. If I shoot in jpeg mode, the file opens up in Photoshop as 35.555 inches wide! This is because compouter montors display images at 72 pixels per inch. So, 2560 / 72 = 35.555 inches image width.

To print this image, I would need a large format printer and the result would be lousy because an image printed at 72 dots per inch is very grainy. If you download an image from the web that was optimized for the web, you'll see what I mean. That 640 pixel wide image 6T5 Cbra mentioned would print out 8.888 inches wide. There's not enough information in 640 dots to spread out over almost 9 inches.

A lot of the images in my gallery are 2560 pixel wide shots. Some were taken with a Nikon CP950 that has a maximum resolution of 1600 x 1200. I used PhotoShop to resize these different sized originals to 500 x 375 600 x 450.

Resizing and resampling are two very different techniques to change the size of an image. If I resize in Photoshop, I just decrease or increase the space between the original pixels to change the image size. THE ORIGINAL DATA DOES NOT CHANGE AND QUALITY IS MAINTAINED. A 2560 pixel wide image resized at 256 pixels per inch becomes 10 inches wide. If I print this 256 ppi image I get an excellent 10" x 7.5" photo quality glossy. At 72 pixels per inch, the EXACT SAME DATA prints out 35.555 inches wide and looks like sh!t.

If you resample the original image, the software program takes the original data and squeezes it together or expands it using an algorithym to decide what data to merge or what data to create ( a guess either way ). This method reduces the quality of the original.

Photoshop has a "Save for Web" command that can take any original image and turn it into a JPEG suitable for web use. The resulting image is always 72 ppi (maximum monitor resolution), but you tell Photoshop how big the image should be in PIXELS and how many kilobytes (quality) the JPEG file should have.

Here is a photo that started out at 2560 X 1920. After ajusting the color, brightness, levels, contrast, etc. I cropped it to 2401 pixels X 1801. I print 10" x 7.5" inch glossies at 240 dpi from this. To display it on the web at 600 X 375 pixels and 38 kb, I resampled it With the "Save for Web" command:

2401 X 1801 resampled to 600 x 375

STG · #4 (**permalink**) 03-13-2003, 04:29 AM

The same original resampled at 800 x 600 pixels at 38kb:

STG · #5 (**permalink**) 03-13-2003, 04:31 AM

Same photo as it comes out of the camera at 72 ppi ( 800 x 600 portion of it, anyway ).

STG · #6 (**permalink**) 03-13-2003, 04:42 AM

None of these pictures will pint out very well unless you put the pixels closer together. 200 dpi is a good minimum, so if you resize the last two 800 pixel wide images (800 pixels / 200 dpi = 4 inches) you will get a decent print. If you print them as is, you get a 800 / 72 = 11.11 inch crappy print.

When scanning, you set the resolution: At 300 ppi, a 10" x 8" original turns into 3000 pixels across. 150 ppi is 1500 pixels across. You choose the scanning resolution. I get the best results by scanning prints at 200 - 300 ppi and then usung the Photoshop methods above to get what I want on the web.

Oh, one more thing. Monitor displays are usually set to 800 x 600 or 1024 X 768 (or....!) so my 800 pixel wide image fills up the screen on some displays, but not on others!

Get it? Got it? Good!

RallySnake · #7 (**permalink**) 03-13-2003, 11:02 AM

Stan,

Nice article, thank you.

Paul