confusion about resolution, scanning, slides etc

[flunn]

A friend of mine who is an artist has put some put images (jpgs) of some of her collages on her personal website. As I understand it the jpgs were made by scanning slides; the photography and the scannning were done by a professional lab.

My friend is disappointed with the results and I sympathize with her: the images are not nearly as sharp as they should be.

Apparently the slides were scanned at 72 dpi; and the people at the lab told her there was no point in using a higher resolution for something that was to be displayed on a computer screen.

This all puzzles me (I know very little about "resolution" and that sort of thing!) For one thing, I've looked at a lot of photography blogs that show full-screen (laptop screen anyway) images that are *very very* sharp. If you can take a photograph of a building or a face and display it big and sharp on a computer screen why can't you take a photo of a painting or collage and get the same quality of result?

Thinking about this it occurred to me that the use of intermediary slides might be the problem. Slides are small so it's not surprising that when they're digitalized and then blown up it the results are blurred. Wouldn't it be better to work entirely from digital images as the photography bloggers presumably do?

Any explanations that would sharpen my understanding of any of this mysterious stuff would be much appreciated.

regards to all from flunn

 

[webado]

A well equipped lab would have had the machine required to convert the image from the negative or a slide slide to a jpeg at a higher resolution. But it's a very, very expensive piece of equipment as far as I know.

If they don't have this equipment what would have been needed I think is to print a photo at the highest quality and size possible given the slide quality, and then scan that photo at the highest dpi possible again, to obtain the jpeg.

Deciding to use 72dpi at scan time seems arbitrary. They could have scanned at 300 dpi or higher and let the user compress the jpegs after that in order to show them optimized on the website. It might compress to 72dpi or even less and still look good - provided it was compressed from a good high quality image.

Is it possible however that the slides were not very good quality in the first place? If you enlarge something that's low quality it gets worse.

 

[jonra01]

The resolution of images is dependent on the output device. The default for jpgs is 72ppi. This has nothing to do with the print resolution. An image that is 720px x 720px would print at 10 inches x 10 inches at 72dpi and at 5 inches x 5 inches at 144dpi. What matters is the overall size.

35mm slide film is 35mm in width. That's a little less than 1.38 inches. If it were scanned at 72ppi that would be about 100px in width. Slides are usually scanned at very high resolution. The usual scan setting for slides can be as high as 4800dpi.

How large are the actual images? Open one of the images and note the actual width of a landscape oriented image then divide that by 1.38. This will tell you the real scan setting. For instance, if the images are 2800px X 2000px then the scan setting was 2000ppi (numbers rounded, so not exact). If they are less than 2000px wide then your friend didn't get what s/he paid for.

The problem may be in how they are resized for showing on a web page. They should be resampled in a photo editing program like Photoshop or PaintShop Pro. If you are putting them on the web server without resizing them and then setting the size in html then they will look pretty bad.

Slide scanners are fairly reasonably priced these days. Many consumer scanners have slide attachments available.

 

[webado]

Define reasonably priced

At work they acquired a high end, high volume, high quality photo lab with all the doodads - a quarter million of equipment plus software costs.
The negative and slide digitizing machine is one expensive (though smallish)component in there. No idea how much but I wouldn't dare touch it seen as I'm such a klutz . I may have to take out a mortgage to pay off the damage :lol:

 

[jonra01]

A scanner is not a photo lab. You don't need a $250,000 photo lab to scan in a few, or even a few hundred slides.

Here's an example of a reasonably priced scanner that can handle slides or negatives. I haven't used this scanner and am not posting this as a recommendation. It is only posted to show that there are options available.

There are flatbed scanners available from Epson, HP, Nikon, and others that have built-in slide holders. Most of these units cost less than $200. You might notice that I didn't include Canon in that list. I've heard negative things about the lower priced Canon scanners when it comes to scanning slides.

Dedicated negative and slide scanners generally run from $200-$500. These are not professional scanners, but are certainly capable of serving the purpose for a small shop or individual. The Nikon CoolScan runs around $500 and is suitable for most purposes. Plustek has one that costs around $200. The reviews of this unit are fairly good.

You can also order a Kodak PhotoCD made from your slides or prints. This is an option if you only have a few that you need digitized. If you have dozens or hundreds that need to be converted then it makes more sense to purchase a decent scanner and do it yourself.

Do the research before purchasing and you should be satisfied with your purchase. Be lazy and buy one without bothering to make comparisons and you might get burned.

 

[flunn]

still trying to understand

Thanks to Chris and Jonra for their replies.

I was interested in Chris' idea of making a good print and then scanning *it.* This certainly seems like a straightforward and comprehensible solution. I'll suggest it to my friend.

I found what Jonra said interesting and to a certain extent illuminating. But I must confess I didn't understand it well. The paragraphs below were written in an attempt to get it straighter in my mind and to ask a couple of questions, but I fear that I have only succeeded in revealing my own ignorance and confusion. If anyone knows of a book or website with a good beginner-level explanation of this stuff, I'd really appreciate the information.

If I understand Jonra, he's saying:

If a slide (or anything else that's 1.38 inches wide) is scanned at 72ppi then, when the resulting jpg appears on a computer screen (the "printing" jonra refers to is, I assume, printing on the screen), it's going to be about 100px wide. If it's scanned at a higher resolution, say 144ppi, it's going to appear smaller. (Presumably, however, if there *were* only 72ppi on the computer screen, the 72ppi image would look the same as the 144ppi image.)

Jonra asks "How large are the actual images?" Does this mean: "How wide are they in inches or centimeters when they appear on the screen?" But in the next sentence he refers to the size of the images as measured in pixels. (I'm confused.) Matters are further complicated by the fact that the images appear in two sizes on the website once as "thumbnails" and once in a blown-up version.

Jonra also mentions the possibility that the problem lies with how the images were resized for showing on a web page. Yes, I think this may have something to do with it. (Presumably this is something that would be done by the person making the webpage, not by the lab that did the scanning.)

One other thing: Neither Chris nor Jonra explained why it was necessary to use slides at all in trying to get good images of art work for display on the web. I'm really puzzled about this.

regards to all from

flunn

 

[webado]

It is most certainly not necessary nor desirable as far as I am concerned to use slides.

But I thought I understood from your original post that slides were all that was available. Thus I deduced no negatives nor prints were available.

If there are already good prints they can be scanned by anybody. Negatives can get printed nicely in a photo lab first and then you scan them at home.

Surely by now everybody and their uncle have a scanner. :lol:

 

[geordie joe]

Apparently the slides were scanned at 72 dpi; and the people at the lab told her there was no point in using a higher resolution for something that was to be displayed on a computer screen.

Translated into plain english that means "Our scanner only does 72 dpi"

If you can get access to a scanner that does better than 72 dpi try it and see.

 

[webado]

Mine does 1200 - whether that's any help I don't know. I use up all the memory when I try it that high so I've never relaly used it. I think 600 is the higehst I've ventured. Overkill


But 300 is usually excellent.

 

[geordie joe]

A well equipped lab would have had the machine required to convert the image from the negative or a slide slide to a jpeg at a higher resolution. But it's a very, very expensive piece of equipment as far as I know.

Model: HP Scanjet 4070

Introduction

HP Scanjet 4070 Photosmart Scanner provides an easy way to quickly convert stacks of traditional photos, 35 mm slides or negatives into digital files for printing, e-mailing, and storing. Scans at 2400 dpi optical resolution and 48-bit colour.

Benefits

* Scan regular photos, four 35 mm slides, negatives, and more
* 2400 dpi optical resolution and 48-bit colour
* Scan four 35 mm slides or negatives at a time

Brand new and only £33 on ebay.

 

[geordie joe]

Surely by now everybody and their uncle have a scanner. :lol:

I have an HP 2400, and it's very good. However, it was bought for one particular job, about a year ago and since then has probably been used about twice.

Probably the least used computer "bit" I've bought. But when you need a scanner nothing else will do.

 

[webado]

Uh? My basic scanner was $150. No slides or negatives.

But I just bought a new printer that comes also with a scanner/photocopier - haven't instaleld it yet. I'll see if it has more features than my standalone scanner. That one doesn't work with Vista

Which is why I needed a new one so I picked the printer/scanner combo since it also prints directly on cd's. Confusion reigns supreme

 

[jonra01]

...If I understand Jonra, he's saying:

If a slide (or anything else that's 1.38 inches wide) is scanned at 72ppi then, when the resulting jpg appears on a computer screen (the "printing" jonra refers to is, I assume, printing on the screen), it's going to be about 100px wide. If it's scanned at a higher resolution, say 144ppi, it's going to appear smaller. (Presumably, however, if there *were* only 72ppi on the computer screen, the 72ppi image would look the same as the 144ppi image.)...

Nope, you've got it confused. Let's use a 1 inch x 1 inch image for simplicity. If you scan it at 72ppi the scanned image will be 72px X 72px. If you scan it at 144ppi then the scanned image will be 144px X 144px and appear twice as large on a computer screen (that assumes the screen uses 72ppi which is not actually true most of the time, but that's a different discussion). If you scan it at 300ppi then the scanned image will be 300px X 300px, and so on... What matters is the size of the image in pixels. When I say size I'm talking about dimensions - width and height.

If you open an image in a photo editor it will show the size of the image. If you use Windows XP all you have to do to see the dimensions is open the folder the image is in and then hover over it with your mouse pointer.

Jonra asks "How large are the actual images?" Does this mean: "How wide are they in inches or centimeters when they appear on the screen?" But in the next sentence he refers to the size of the images as measured in pixels. (I'm confused.) Matters are further complicated by the fact that the images appear in two sizes on the website once as "thumbnails" and once in a blown-up version.

Jonra also mentions the possibility that the problem lies with how the images were resized for showing on a web page. Yes, I think this may have something to do with it. (Presumably this is something that would be done by the person making the webpage, not by the lab that did the scanning.)...

When I ask how large the actual images are I'm talking about the images that were provided by whoever scanned them in the first place - the digital images. How many pixels wide and how many pixels tall? The size they are displayed at on the web page should be whatever size they are after resizing the originals.

For example, let's say the professional lab provided images that were 3000px by 2000px. That's far too large to use on a web page so they should be resized to something like 700px by 467px and saved as a copy. If you need thumbnails then resize the image again to something like 100px by 67px and save as a copy (those are approximations). You should still have your original 3000px x 2000px image. When you place the image on the page you put the dimensions in the image tag. If you use a wysiwyg html editor it will probably do this for you.

The most common mistake that people make when placing an image on a web page is to upload a large image and then resize it in html. This will almost always give poor results. The browser has to reinterpolate the image to match the size specified in the img tag. Browsers do a lousy job of this. You can avoid this by resizing the image before uploading it to the server and then using the exact size in the html code.

... One other thing: Neither Chris nor Jonra explained why it was necessary to use slides at all in trying to get good images of art work for display on the web. I'm really puzzled about this.

regards to all from

flunn

The only reason to use slides is if that's all you have to work with in the first place. I very much doubt that the lab did it that way unless it was done several years ago. Most would use a digital camera for this purpose. This would be a lot easier if you could provide a link to one of the images and even more helpful if you could provide a link to a page with the image on it.

 

[JWJ]

To give you some idea of what you can expect, look at these sample photo's I have scanned for you. The slides are about 25 years old and of my daughter, who would skin me alive if she knew I was putting her up on the net. My scanner is a modest HP that cost me about £170 GBP about 6/7 years ago (best guess). It has a Transparency Adaptor that can scan up to 4 35mm slides at a time. The default resolution is 200 ppi which I used for the first picture and the second one is at 1200ppi (the highest setting). The third photo is at 75ppi. All have been sized to 600pxs wide for comparison purposes. Clicking on each photo will show you it's original size.

The difference between them is quite noticeable, especially on the wire-frame door and the wicker basket. It is not hard to appreciate that resolutions well in excess of 1200 are necessary if any degree of quality is sought. Conversely, it is also easy to see that 72ppi is a non-starter.

Given the comparative costs and technical improvements that one can expect from today's machines, I would expect that a fairly reasonably result should be achievable without breaking the bank. Like everything else, it all depends what end result you are seeking. For my old keepsake family snapshots I will be happy enough using this equipment and scanning at a mid-resolution of 600ppi but for anything more serious I would be considering a new machine with 4800ppi capabilty.

Hope that helps. :wink:

 

[jonra01]

There is a lot of confusion on this subject. I see discussions about it quite often on stock photo sites. Someone will point out that an image is listed as 72ppi and ask for a higher resolution image for printing. Someone then has to explain to them that the listed resolution has nothing to do with the resolution that is used for prints.

A jpg image can be saved at whatever resolution you like, although most of the time they are saved at the default 72ppi. What matters is the overall dimensions of the image. An image that is 3000px X 2400px can be printed as a 10" x 8" image at 300dpi. The same image can be printed as a 5" x 4" image at 600dpi. This all has to do with printing. When it comes to showing on a monitor it is not quite the same. A monitor is limited by the resolution setting. The one I'm looking at right now is set to 1280 x 1024. A 3000px image would obviously not fit on such a screen. If I resized that image to 1280 x 1024 then it would fit exactly.

When dealing with screen images you are dealing with ppi (pixels per inch) and monitor resolution. Monitors and operating systems vary when it comes to the actual pixels to inch ratio. Most Windows systems use a 96ppi setting. I have no idea why the jpg format settled on a 72ppi default. Regardless of that fact, all you really care about for screen display is what percentage of the screen the image will occupy - you are dealing with pixels.

Printing deals in inches and dpi (dots per inch). The larger the overall size of a digital image the larger the final print at a specific dpi. The higher the dpi the smaller the final image on paper.

So, the lab people that said 72ppi was high enough were right. They were probably talking about the apparent resolution of the jpg images and not about what resolution was used for scanning.

 

[flunn]

thanks to jwj and jonra01

Many thanks to JWJ and Jonra01 for their March 5th postings about scanning, screens, pixels, dpi etc.

I've been away from the forum for a few days and have seen these postings just now. it will take me some time to digest them, I think. When I've done so, I'll be back with more questions. (And I hope slightly less confused ones!)

regards to all from flunn