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Old 06-22-2008, 01:36 PM   #1
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On preparing photos for e-ink screens

After getting a number of emails from folks in various forums, I thought I would post this for those of you interested in transferring photos to you e-ink readers.

I only have a Kindle, and don't know if or how you can put photos on any other readers, and this post isn't about how to do the transfer, that's already been covered in other posts by other people.

This is about how and why to do prep work on your photos before you transfer them.

First, before you do anything else, resize and crop your photo to the proper dimensions for your device. On most or all e-ink readers at this time, that is 600 wide by 800 high. Not 639 x 845, not 596 x 801 .... 600 by 800.

I've got two methods for cropping and resizing that have always worked well for me.

For portrait photos (taller than wide), I generally first set the height to 800. Most graphics programs will automatically calcuate the width (assuming that you intend to keep the original proportions). If the width comes up as a value less than 600, then I set the width as 600 and let the computer calcuate a height something greater than 800.

Then, I crop the image ... either the height or the width, so that my resulting image is exactly 600 x 800.

Another method I sometimes use when I'm just not certain how I'm going to want to crop or resize is to create a blank image that is 600 x 800. I then copy and paste the image I am working with into that blank frame ... and move it around until I get an image I like.

The next thing that you need to understand is ... e-ink can't display any more than 4 levels of gray. That's it ... that is your palette. Yes, you can copy a color image onto your e-ink device ... it just won't display very well. That's because the screen takes all the colors within a certain range of contrast ... and makes them all the same shade of gray. What you get is murk.

In addition, just making a color image "black and white" does not solve the problem. This is because most "black and white" images on a computer are 256 levels of gray. So, put it on your e-ink screen, and you have the same problem .... the screen has to reduce 256 levels down to four and you have murk again.

It's not enough just to increase the contrast ... in the end you will lose much of the detail you want ... especially in a photo.

So, how to solve the problem? Depending on your graphics program, it can be quite easy. Others make it harder than it needs to be. My program of choice to do this is Paintshop Pro version 8. Yes, I've got Photoshop ... but I always use the easiest and fasted tool to do the job. And, in this case it is PSP 8 .... which is a dirt cheap buy on eBay.



Step one is to reduce the color photo down to 256 shades of gray. In PSP this is image/grayscale. In PS it is image/adjustments/black and white. You can also use image/mode/grayscale.

http://www.geocities.com/ricky1750/Graphics/A62Egs.jpg

OK ... so now we need to check the contrast. If at all possible, you want to have an image that has a good range of dark to light. If everything is nearly the same shade of gray ... reducing it to four shades isn't going to make it a better image ... but worse.

So, in both programs you play with what are called "curves". In PSP the command is adjust/brightness and contrast/curves and in PS it is image/adjustments/curves.

The idea is to drag the curve around until you get an image that gives to a good range of dark to light, but still allows you to see detail.



Once you get the contrast set the way you like it, then we get to the meat of the problem .... reducing the levels of gray. With line art, it's fairly simple ... you can just "posterize" to four levels. Most graphics programs have a posterize command.

HOWEVER .... posterize works horribly on most photos. It will wipe out most or all of your detail.



What you should do in order to preserve your detail is something called "dithering" ... essentially it makes you photo look more like something out of a newspaper. What you are doing is creating the illusion of more gray scales using just the four you have.

In PSP, the command is image/decrease color depth/x colors/number of colors = 4/optimized median cut/error diffusion



You can still see the boy's eyes under the shadow of his cap. Much better than posterized.

In PS, use the command file/save/save for web & devices. Set the dither to 100%, colors to 4, palette to perceptual, and diffusion.

I have found that, when using Photoshop, it is necessary to play with the curves to adjust the contrast more often than it is with PSP.

In any event, it does not take long to prepare a photo for e-ink, especially not once you are used to doing it. And, a little bit of prep work makes for a much better display.

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Old 06-22-2008, 02:21 PM   #2
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Four shades is true of the Cybook, but not of the PRS-505, which does 8, or of the Iliad, which does sixteen.
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Old 06-22-2008, 02:28 PM   #3
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With ImageMagick, you can use -resize 600x800 and it will automatically choose the correct size (i.e., maximum 600 width and 800 height).

When it comes to reducing the number of colours, you can use the -map option, which gives the exact colours to be used in the output image (that's good if we know which are the exact grey intensities the eBook screen will display).
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Old 06-22-2008, 02:52 PM   #4
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Quote:
Originally Posted by comtrjl View Post
Four shades is true of the Cybook, but not of the PRS-505, which does 8, or of the Iliad, which does sixteen.
In which case, in order to get the best presentation of your image on those screens, you should reduce the number of levels to either 8 or 16.

This is an example of both posterization and dithering at 8 levels:





and the same thing at 16 levels:





You might even be able to get away with posterization at 16 levels of gray, but I would submit that the dithered photo looks better.

Last edited by RickyMaveety; 06-22-2008 at 03:05 PM.
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Old 06-22-2008, 02:54 PM   #5
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Originally Posted by Jellby View Post
With ImageMagick, you can use -resize 600x800 and it will automatically choose the correct size (i.e., maximum 600 width and 800 height).

When it comes to reducing the number of colours, you can use the -map option, which gives the exact colours to be used in the output image (that's good if we know which are the exact grey intensities the eBook screen will display).
So, if I hear you right, you are saying that ImageMagick will also automatically crop the image so that you end with a 600x800 dimension?

And, does the user have no control over the cropping?? Because I'm not certain that would be a plus.

Here I've taken the photo and simply resized it to 600x800 without appropriate cropping.



End result ... the kid gets distorted.

This is as opposed to cropping and resizing in a manner that preserves the subject of the image ... (the example is done in 4 levels of gray).


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Old 06-22-2008, 03:49 PM   #6
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Quote:
Originally Posted by RickyMaveety View Post
In which case, in order to get the best presentation of your image on those screens, you should reduce the number of levels to either 8 or 16.

This is an example of both posterization and dithering at 8 levels:

http://www.geocities.com/ricky1750/Graphics/A62E8p.jpg

http://www.geocities.com/ricky1750/Graphics/A62E8gs.jpg

and the same thing at 16 levels:

http://www.geocities.com/ricky1750/Graphics/A62E16p.jpg

http://www.geocities.com/ricky1750/G...s/A62E16gs.jpg

You might even be able to get away with posterization at 16 levels of gray, but I would submit that the dithered photo looks better.
In my experience you don't want to dither too early if a all. Dithering fills the image with little white or black dots to try and achieve additional gray levels. Once done it is not reversible. Usually I try to avoid dithering but if I need it I reduce the colors to 256 and then grayscale prior to attempting any dithering. I will also try and balance the image so that everything is not at one end of the darkness spectrum. It is a bit of art but the resutls can be pretty good. I usually don't drop below 16 levels and let the device itself do the final reduction if needed. After all you might buy a better device in the future.

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Old 06-22-2008, 07:27 PM   #7
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In my experience you don't want to dither too early if a all. Dithering fills the image with little white or black dots to try and achieve additional gray levels. Once done it is not reversible. Usually I try to avoid dithering but if I need it I reduce the colors to 256 and then grayscale prior to attempting any dithering. I will also try and balance the image so that everything is not at one end of the darkness spectrum. It is a bit of art but the resutls can be pretty good. I usually don't drop below 16 levels and let the device itself do the final reduction if needed. After all you might buy a better device in the future.

Dale
I too first place the image in grayscale. It's a very (very) bad idea to try to reduce colors on a color image ... unless you are trying to posterize and you don't mind getting some really funky results.

I never dither until I am absolutely satisfied with the contrast in the image. In addition, I always work on a copy of my original image. I never do anything to an image that cannot be undone.

However, dithering can be undone by any graphics program with an undo feature. In addition, most will allow you to preview the dither before you do it.

Since I will not be putting thousands and thousands of pictures on my e-book, I don't much worry about taking the images all the way down to 4 levels. If I want to take the same images and make them 16 levels some day because I've gotten a different reader ... I'll do it then. It takes less than 30 seconds for me to reduce an image. Further, it can be done in certain programs as a batch process (both PSP and PS allow for this).

Having the e-book determine how it is going to display the additional levels of gray that are beyond its capacity may work for you. I prefer the control that comes with knowing exactly what will be displayed, but then graphics are my passion.

In fact, I noticed when I downloaded the Beatrix Potter books from PG, that the images display very badly on the Kindle. I doubt they are much better on a 16 level display. That is why I am now preparing my own editions of these books, with illustrations that are (I hope) optimized for the Kindle.

Hey .... you know, some people are anal about justification, others about the color of their e-book. I am anal about graphics.
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Old 06-22-2008, 08:08 PM   #8
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The 505 can also rotate the image so you can get it landscape or portrait depening what's best for the aspect ratio. Also, I've found the 505 does a very good job of dithering on it's own. So if you want to reduce the photo to 356 shades then the 505 will do a nice job displaying this using it's own internal dithering. No need to downshift to only 8 shades.
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Old 06-22-2008, 09:28 PM   #9
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The 505 can also rotate the image so you can get it landscape or portrait depening what's best for the aspect ratio. Also, I've found the 505 does a very good job of dithering on it's own. So if you want to reduce the photo to 356 shades then the 505 will do a nice job displaying this using it's own internal dithering. No need to downshift to only 8 shades.
Well, that's a handy trick then. I haven't found that the Kindle dithers very well, but then maybe I need to experiment more.

It would be interesting to see photos on the various devices, either in 256 shades of gray or reduced to the level of gray intended for that device, and side by side for a comparison. Same photo, different set ups ... different devices.

I'm still too much of a control freak to have the ebook decide on how my images are displayed ... but again, that's just me.
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Old 06-22-2008, 09:36 PM   #10
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if I can remember, I'll try to get some photos of my 505 showing photos.
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Old 06-22-2008, 10:21 PM   #11
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if I can remember, I'll try to get some photos of my 505 showing photos.
I'd like to see them. I think the automatic rotation is an interesting idea ... although, I just make certain that the images are properly rotated before I put them on a Kindle.

You know what would really be a help?? Download The Tale of Samuel Whiskers from this site (or PG ... whatever works), and display one of the color images on your ebook.

I would really like to see how well one of the images (like the one of the chimney and roof with the hills in the background) that isn't very high contrast displays.

I'm working on that book right now and converting the color plates to dithered 4 level gray scale, which I think looks much better. That's the screen shot I could really use.
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Old 06-23-2008, 03:59 AM   #12
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So, if I hear you right, you are saying that ImageMagick will also automatically crop the image so that you end with a 600x800 dimension?

And, does the user have no control over the cropping?? Because I'm not certain that would be a plus.
No, it does not crop anything. It resizes the image, keeping its proportion, so that it fits in a 600x800 screen (the width is less than 601 and the height is less than 801).

A 1000x1000 image will be reduced to 600x600.

A 500x1000 image will be reduced to 400x800.

A 300x100 image will be enlarged to 600x200 (but you can use "-resize 600x800\>", and then it will not be changed.
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Old 06-23-2008, 04:15 AM   #13
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One tip - if you're going to resize an image, make sure that it's in 24-bit colour before you do the resize. Resizing with a limited colour palette will give poor results. Only convert to grey-scale once the image is the correct size.
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Old 06-23-2008, 03:45 PM   #14
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Four shades is true of the Cybook, but not of the PRS-505, which does 8, or of the Iliad, which does sixteen.
The PRS-505 is 8bits so thats 2^8 = 256 shades.
I don't think the cybook is 4 shades is probably 4bits, like the Kindle. So that would be 2^4= 16 shades.


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Old 06-23-2008, 04:10 PM   #15
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The PRS-505 is 8bits so thats 2^8 = 256 shades.
I don't think the cybook is 4 shades is probably 4bits, like the Kindle. So that would be 2^4= 16 shades.
PRS-505 is 3-bits (8 shades), most other devices with 6" screens are 2-bits (4 shades) and the iLiad is 4-bits (16 shades). This is what gets displayed on the screen, they all accept 8-bit or more images and color images.
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