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Technical Questions

How to correct this

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gordg3
 
Posts: 42

How to correct this

Post Tue Oct 20, 2009 3:02 am


I just purchased a canon 14mm f/2/8 lens. When shooting a deep blue sky in raw mode it looks fine in RAW and JPG (large). When I shrink it to 11.333 x 17 inches (72 dpi) JPG the sky shows gradient lines. Any suggestions? Here is the image: http://www.pbase.com/gordg3/image/118460016. I would like to continue shooting in the highest resolution.

prinothcat
 
Posts: 662

Re: How to correct this

Post Tue Oct 20, 2009 3:24 am


how are you doing the Jpg compression? That look like a compression artifact, not necessarily a problem with the base image.

dougj
 
Posts: 2276

Re: How to correct this

Post Tue Oct 20, 2009 4:33 am


In addition to Chris' comment, when you do your post processing, are you using 8 or 16 bit mode?

gordg3
 
Posts: 42

Re: How to correct this

Post Tue Oct 20, 2009 4:44 am


I do some processing in RAW mode use Canon Digital Photo Professional 3.6.1then convert and save to 8-bit JPG. I finish whatever processing is need and resize to 17x11.333 at 72 dpi and save using "baseline standard" in PS3. I am sure it is from the compression as the RAW image and large JPG (after conversion in Canon DPP) shoes no artifacts.

dougj
 
Posts: 2276

Re: How to correct this

Post Tue Oct 20, 2009 5:31 am


A suggestion - if you intend to do processing after DPP, try saving the photo in 16-bit TIF format and use this in PS, this will reduce the loss of detail and subtle tones. I don't know if DPP can directly send an image to PS3, the CS versions have enabled this and they transfer as a 16-bit TIF.

A minor point - for use on the web the physical dimensions and DPI do not come into play, these are more relevant to printing and 72 DPI is too low.

gordg3
 
Posts: 42

Re: How to correct this

Post Tue Oct 20, 2009 5:44 am


Thanks. I saved the image as a 16-bit TIFF. Did the processing in that mode then used the "save for web" command and that did the trick. Thanks for the responses. I appreciate them.

dougj
 
Posts: 2276

Re: How to correct this

Post Tue Oct 20, 2009 10:37 am


I'm glad it worked for you. Chris is definitely right that compression can seriously degrade a photo and we'll see it in banding, etc. Also, a photo with very subtle changes in tones, like a sky, may need more than 8 bit limitation of 256 steps/shades per color, so we see steps, banding or sometimes blotches in some areas. 16 bits gives us 65,536 shades of each color, and more is better in this case. Processing in 16 bit from start up to the finish helps avoid this, then convert to 8 bits for web use at the end. If you're printing, I suggest to stay with 16 bit TIF.

Here's an article from Photoshop Essentials that discusses this, the examples they have are not as pronounced as a sky, but the effects are the same.
http://www.photoshopessentials.com/essentials/16-bit/

gordg3
 
Posts: 42

Re: How to correct this

Post Tue Oct 20, 2009 5:10 pm


Thanks. Is it just me or is the website having a problem displaying EXIF info. I just uploaded an image and there is no EXIF data today. There was no problem yesterday. Can someone else confirm.

sheila
 
Posts: 1303

Re: How to correct this

Post Wed Oct 21, 2009 1:12 am


I could be that CS3 "Save for web" still strips the EXIF data from images whereas CS4 doesn't. I may be wrong..I think I was once about 20 years ago :lol:

Sheila
Sheila Smart
Canon 5D Mark III; 17-40L; 24-70 f/2.8L; 70-300 f.4-5.6 L USM; 135 f/2L; 100 f/2.8 macro; 8-15 f/4 L fisheye

Blog: http://sheilasmartphotography.blogspot.com/

gordg3
 
Posts: 42

Re: How to correct this

Post Wed Oct 21, 2009 5:46 am


Yes it does. I must have been doing something differently to get the EXIF information to show up on the web page. Anyhow experimenting with different compression. To display some images I will just have to load larger (quality) sized images converted from from TIFFs.

waggonerphotos
 
Posts: 176

Re: How to correct this

Post Wed Oct 21, 2009 8:07 am


Question? If you downsize your image manually to say 800px on the long side, then use the save as command rather than the save for web, would this still strip your exif data?
Bob Waggoner
Photographs comprise the communal memory of our times. (Unknown)

ernst
 
Posts: 537
Location: Maastricht, Netherlands

Re: How to correct this

Post Wed Oct 21, 2009 11:25 am


waggonerphotos wrote:Question? If you downsize your image manually to say 800px on the long side, then use the save as command rather than the save for web, would this still strip your exif data?

No, it doesn't. All info will be there after uploading to Pbase. :D
This is how I prepare my photos too and I am happy with a file size approx. 200 kB, but with minimum jpg setting of 8.
By the way, don't forget to sharpen (a little bit) after downsizing...


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