Resizing digital pictures

“I would like to resize some images taken at 4megapixel resolution. Any advice on software or, better yet, websites that will allow me to do this?

There is a new website for outdoor photos in Alabama, but the max res they will let you post is 1000x700. I need to make my photo "lose" resolution to get down to that size.”

“Did your camera not come with some photo manipulation software? That is such a simple task, it's a pretty standard feature.”

“It probably did. I have fiddled with the software before and it really sucked for what I was using it for which was removing red-eye. The software is loaded at home, so I'll take a peek when I go home for lunch.”

“Before I got a digital camera (and was just scanning photos at work), I found a free program from Serif, which I still use. You can buy more complex programs, but I still use their free package - it's really easy. I just resized a photo 5 minutes ago - just clicking on their Image menu, Resize, then entering the width pixels (and keeping the same aspect ratio box checked) - bingo, done. You should be able to hunt around on their web site and find it.”

“In Photoshop, to post on the web, I downsize photos to around 4x3" (I don't know how to put that in whatever measurement you gave above). I put the dots per inch at 200, but I'm guessing you could go as low as 72, which is the screen resolution.

And then I compress the hell outta them. I do a "save as" and Photoshop has the option of put them at a compression level of 0 (way, WAY compressed) to 12, basically no compression.

I move the slider. It will give the KB size as it moves. I try to get it around 100 kb.

Saves loading time on the net... and prevents someone from stealing a good photo to use for themselves, cuz the downloaded resolution will be so bad.

One free online program that does some stuff like that, which I use to view photos, is Irfanview. I think you'd find it at www.irfanview.com”

“I didn't know that Irfanview was still out there. I have that and it works pretty good for most stuff.”

“A really nice program that lets you do all kinds of things with Photos is Photoshop Elements 2.0 $89 at Costco and other big stores.”

“Thanks everyone. This is just what I was looking for.”

“Hmmmm, bit maybe it's not. I just figured it would be. And I always liked the program icon of the dead cat with tire tracks across it. hehehe”

“I just checked.... one of the most popular viewing programs around, it says.

I don't know if it resizes. You should be able to do some color and other types of manipulation. I had one of our new, very PT reporters use that program for her photos a year ago.”

“I did a quick websearch, and it's still there.

”

“i use infranview”

“Damn quotes...

Irfanview”

“Rfranview worked great. Thanks for the link.

bit - there is a new site called picturealabama.com It's new and has only a few pics so far.”

“I'll check it out...”

“This is probably the best of the bunch

http://www.picturealabama.com/gallery/details.php?image_id=4”

“That one is nice.”

“I have and use about five or six sites and programs to work with my photos. I always come back to ACDSee. They will let you use it free for about 90 days. Try it. Another one is Mircosoft Digtal Image 7.0. Two free programs are Ofoto and Shutterfly which yuou can use for albums or making prints. And Adobe will let you use Photo Shop starter addition for free. Download a lot of them and play with them. have fun! "I am and remain, the Dodder."”

“Adobe Photoshop is good I used it for years.

However, I now prefer Paint Shop Pro and it's a lot less expensive.

Both have a learning curve for editing and touching up pictures.

One thing to remember, If you put a 1200 dpi pic on the net for viewing, it:

1. Is going to take a long time to dload for someone with dialup.

2. The resolution is ony going to be as good as the monitor someone is viewing it on.

As far as scanning and printing goes:

olor printers are similar to B&W printers, in that they must print several of the printer's dots for each image pixel (except for dye sublimation printers, which can make any color on any printed dot). Inkjets have only 3 or 4 colors of ink, a few have 6 colors, and this is all they can print. They CANNOT print any one of 16 million colors on any one dot. So to represent each image pixel in various colors, shades, and intensities, the image is dithered, meaning the printer uses a pattern of several of its dots to simulate the color of each pixel in the image.

For example, to print one "pink" pixel on our inkjets, we know it must mix some red and some white. There is no white ink, white is the paper color, no ink at all. But to make red, the printer only has the CMYK (Cyan, Magenta, Yellow, and blacK) ink colors, and so must use a few magenta and yellow ink dots, not necessarily equal numbers of each, to achieve a certain shade of red. To make lighter shades of red, blank white space is used in the right amount. Black ink dots are used to darken some colors. The average visual effect of all these individual dots of magenta, yellow, white paper, and perhaps black ink too, looks pink to us. But all of these multiple ink dots represent or simulate the color of only ONE pink image pixel.

So it is clear that we don't get anywhere near 600 or 720 dpi of "image" resolution from our printers in Color mode. This requirement for multiple printer dots for one image pixel greatly reduces the printer's real image resolution capability to a fraction of the printer's advertised dpi. Printer specifications are real and accurate and meaningful, but are not to be confused with image resolution. Printer ink dots and image pixels are simply very different things, and one color image pixel requires many printer ink dots. This is why we need a 600 or 720 dpi printer to print an image at 150 or 200 dpi. And like B&W printers, attempting higher resolutions on color printers simply limits the pixel size area, allowing fewer ink dots, which then limits to even fewer possible color tones. We need the several ink dots in that space to simulate the correct color of the pink image pixel.

And like B&W printer halftones, if a higher resolution grid is used, then fewer colors can be represented in that space. If you attempt to print at higher values than the printer is designed for, say 360 or 480 dpi, then you are only allowing space on the paper for a very few ink dots per pixel. The color accuracy is reduced (fewer possible values of color tones in that space).

Our home color inkjet printers do not require the four CMYK halftone screens (Cyan, Magenta, Yellow, and blacK) from an imagesetter like commercial printing presses use. Instead, our home printers expect RGB images, and the drivers use dithering (error diffusion or stochastic) to produce the color combinations from 3 ink colors. Basically, dithering is the use of scattered dots, somewhat randomized instead of ordered halftone grids, and it looks smoother. The printers limited combinations of 3 ink colors can rarely make the exact color for an image pixel. There is an error, the difference in the desired color in the image, and what the printer can do. Error diffusion means that the color error difference is carried over to four adjacent image pixels, to the right and below the pixel in error. Those next pixels are intentionally overcompensated in the opposite amount. If the one pixel is not pink enough, the next neighboring pixels are made overly pink, so to speak. Then their own error term is carried over to their neighbors in turn, etc. As this process moves across the image, compensating the color error, it all balances out and we see the right color. Error diffusion needs less resolution than the 1.5 x lpi factor, perhaps 1.2. Kodak's claim for stochastic dithering is that it needs far less, perhaps only a 0.75 factor (page 14 of ( Optimizing Photo CD Scans for Prepress and Publishing, an Adobe Acrobat .pdf file, 376K bytes).

Stop and think about it a second... Scanned images obviously look much better on the monitor than on the printer. And yet we think the printer requires greatly MORE resolution than the screen? Their images are often larger (in pixel dimensions), but printers are still rather crude devices. The big difference is that the monitor screen shows continuous tone RGB images, but the printer must simulate each pixel with many printed dots, each dot of a single CMYK color.

Bottom line:

Printer "dpi" is a different thing from image dpi (except in Line art mode).

For inkjet or laser printers, here are good scaling guidelines for Color or Gray Scale photographs:

300 or 360 dpi printer - use 60 to 120 dpi image.

600 or 720 dpi printer - use 120 to 240 dpi image.

This statement is made for Grayscale and Color modes. Note the exception for line art mode, which is 1-bit 2-color (B or W, like ClipArt or fax), which contains no gray, no halftones, no dithering. In line art mode, the printer CAN use its full resolution, making use of the full resolution of the scanner. Because in line art mode, every image pixel is either Black or White, so there is no dithering necessary to simulate intermediate tones. Line art is the one mode that the printer can use an image resolution equal to the full resolution of the printer. If you have a 600 dpi printer, then 600 dpi line art can be printed advantageously to reduce the visible jaggies.

But for Color or Gray Scale modes, the dpi guide above is appropriate. Generally the middle of the range above is about right, but modern Color dithering may use a few dots less per pixel than B&W halftones, so Color may be best towards the high end. I've exaggerated the high side, and I'd bet on the midpoints instead in most cases. Actual printer dpi divided by 3 or 4 is the correct range.

I'd suggest scaling to
100 or 120 dpi for older 300 dpi inkjets,
120 to 170 dpi for 600 dpi laser printers,
180 to 300 dpi for today's better color ink jets on the best paper.

Scaling to more printed resolution than this won't often be very helpful. A little less than this is often just as good. Paper varies. Images vary too, some are sharp and some are not. The low end of the range is often fine, experiment to see if you can tell the difference. Giving the printer huge images can be pretty slow, it takes the printer time to receive and discard all of those pixels. Note however that if you are printing the printed image larger than the original photo, then the scanning resolution should be increased accordingly, in the same ratio as the image size (see Scaling in the previous section).

Note that if you are printing the printed image larger than the original photo, then the scanning resolution should be increased accordingly, in the same ratio as the image size increase, to achieve these same numbers (see the previous section). This means you might scan at 300 dpi and scale to 150 dpi to print at 2X size.

Inkjet printers have come a long way in the last couple of years, and the once impossible photo quality is taken for granted today. The 6-color photo inkjet printers became the state of the art for printing photographs at home. They add light magenta and light cyan ink to provide more choices to help color accuracy, and to help hide the dots in the light areas. These photo printers in some cases can take advantage of higher image resolution. The current best inkjet printers also have smaller ink dot drop sizes available, and these also help simulate the lighter colors. So 6 ink colors is less important on the newest printers today.

Epson is suggesting printing images at 240 dpi if maximum possible detail is desired on the best glossy paper. 240 is 720 / 3, to account for the several dots required to dither the 24 bit RGB colors of each image pixel, and corresponds to lpi x 2. Experiment with 240 dpi on your sharpest images, but also experiment to see if 180 dpi will give the same results (180 dpi corresponds to lpi x 1.5 and also to 720 / 4). Many of our snapshots really don't have maximum sharpness, and don't need maximum resolution, and frankly, 150 dpi is often plenty. But some certainly can use more. The 240 dpi is a maximum limit of usefulness, and not necessarily a "gotta have" goal in every case.

HP inkjets are 600 dpi, but this is not comparable, because they use a unique REt technology that blends colors by printing several ink drops on any one dot. A pixel's color value is dithered on the same one dot instead of by a group of dots. Some of these possible combinations are murky, but each dot can still make many useful colors (instead of one color) and error diffusion dithering still corrects any error. It is not continuous tone, but it's rather close. Printer dots and image pixels can be matched one for one, like on a monitor but with higher color error. Printing images at 300 dpi is indeed realistic now. In particular, the very first thing the first PhotoSmart printer driver did was to upsample the image to 300 dpi to match the printer's internal 300 dpi image grid, and it was amazing. It can in fact be seen that for the sharpest images, the PhotoSmart could show improved detail if given a 300 dpi image in the first place. But you have to look mighty close to detect it.

You'll still hear a lot of strange things on the internet, including many comments about how some users claim to scan color photos at 600 dpi or even 1440 dpi!, and WOW, do their printed images look better. Yeah, sure they do, but it's really advisable to test this for yourself, because for one thing, the printers don't have that much image resolution, and for another, neither do the color prints (negatives and slides can). At the extremes, neither do the scanners. So do experiment to satisfy yourself it's true that these lower suggested values will give you all the quality there is to get, so you don't needlessly waste memory or disk space scanning with higher resolution that is NOT useful. The more pixels you give the printer, the more it will discard, and in fact, the excess can be detrimental to the printed image, depending on how skillfully the printer discards the excess.”

“Holy Moly, Batman. That looks like great info. Will have to thoroughly peruse at home tonight!!! Thanks, Redhawk

Let me talk about my own "test" (although it really wasn't). On my Yellow River Forest hike photos, a few expert photo eyes said the photos were very good and sharp. hehehee... I did sharpen a wee bit in Photoshop. But due to the downsizing and compressing, I pretty much thought they looked like crap on my machine... then again, I have a 21" monitor (or something big), so I see them enlarged in Webshots just that much more... which of course enlarges and exaggerates jaggy pixels.

Anyhoo... glad y'all like the camera. I haven't even taken any full-blow, highest resolution, best-quality shots yet. *rubs hands in anticipation*”