Old 06-26-2009, 03:44 PM   #1
David Harrison
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Default What is "Too Much Compression"

This shot has been submitted multiple times for bad cropping. Now I get "Too Much Compression: Using too much JPEG compression when saving pixelates the image."

Please believe me that I do not know what any of this means. I am shooting with a Panasonic FZ50. The telephoto lens is 1:2.8-3.7 / 7.4- 88.8.

I edit on a Mac Book Pro using iPhoto.

Here's the last photo

http://www.railpictures.net/viewreje...&key=969118896

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Old 06-26-2009, 04:51 PM   #2
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Originally Posted by David Harrison View Post
This shot has been submitted multiple times for bad cropping. Now I get "Too Much Compression: Using too much JPEG compression when saving pixelates the image."

Please believe me that I do not know what any of this means. I am shooting with a Panasonic FZ50. The telephoto lens is 1:2.8-3.7 / 7.4- 88.8.

I edit on a Mac Book Pro using iPhoto.

Here's the last photo

http://www.railpictures.net/viewreje...&key=969118896

David Harrison
I'm not actually seeing it in your photo, but my eyes never did see those kinds of details. If I understand correctly, it shows 'blotches' in colors that should be solid.

What causes it-Using 'Save For Web' or when you re-working a rejected photo instead of starting over with the original. Always use the custom Save As, and ALWAYS start over with the original when re-working a rejection, instead of just tweaking the rejected version. Each time you do that, you lose more and more quality.
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Old 06-26-2009, 05:20 PM   #3
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Thanks EMT...I'm not seeing anything either. Yes, I always go back to the original version before attempting a cure of the latest rejection.

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Old 06-26-2009, 05:38 PM   #4
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This is longer than it needs to be but I'm bored... skip down to the bottom if you don't want to read too much.

The JPEG format compresses the data in your image in order to save space. It does this by taking advantage of the fact that colors in images frequently get grouped together.

Imagine that you had a very small 10 pixel by 10 pixel image - in order to save the data for that small picture, an uncompressed image would require 100 memory units (10 pixels x 10 pixels = 100 pixels. Each pixel requires one memory unit). Imagine that the 10 pixel by 10 pixel image you're saving is completely black. If you saved that image as a compressed JPEG file, it would only require one memory unit, because all 100 pixels are the same, so we'd only need to store information for one of them.

Similarly, if you take a picture of a train on a clear, sunny day, JPEG will consolidate many of the blue pixels in the sky into larger blocks. It will look at an area of the image and see something like "hey, these 8 pixels here are all about the same color - let's save some space and apply this blue color to all 8 pixels." Doing this would reduce the number of memory units needed from 160,000 to something like 20,000. Compression applies this process to the entire image - any area with similar colors would be reduced into a larger block of a single color. This is why you'll often see blocky artifacts in the sky portion of your photos - the sky is generally a large area of similar color.

There are varying levels of compression - a high quality image may only consolidate from a group of 4 similarly colored pixels into one block instead of grouping 8 pixels together. The level of compression can be set in your image editor.

In your specific photo, you can see the compression where the image is "blocky," "splotchy," or "pixely." It's very noticeable on the smooth gray areas of the left train, as well as the black corrugation lines on the right train.

There are two causes of excessive JPEG compression
- The image is saved with a high degree of compression (low quality)
- A previously compressed image is reopened and compressed further

To avoid the first cause, make sure you save your images with a high quality setting. I did some googling and it looks like iPhoto will allow you to select a quality setting between 1 and 12 when you save a JPEG. Use 11 or 12 and you'll be all set.

To avoid the second cause, make changes to the original image from the camera, then use "Save As" to save the edited image to a new file. If the new file is submitted and rejected, make the next round of adjustments on the original file from your camera, not the more recent (and more compressed) version you just sent in.

Hopefully that was useful and reduced confusion instead of increasing it.
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Last edited by ottergoose; 06-26-2009 at 09:25 PM.
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Old 06-26-2009, 05:40 PM   #5
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So Nick would that explain why images very in file size when taken with the same camera? (i.e. a more complicated image requires less grouping of colors).
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Old 06-26-2009, 05:43 PM   #6
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So Nick would that explain why images very in file size when taken with the same camera? (i.e. a more complicated image requires less grouping of colors).
Yep, that explains most of it.
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Old 06-26-2009, 06:53 PM   #7
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Hi David,

I don't see it mentioned in this thread and you're probably already doing this, but make sure you are shooting your JPEGs at your camera's maximum resolution. Most camera's have 3 settings for size and resolution. You want to max those settings out. Typically, the best quality is referred to as Large, Fine JPEG.

If you shoot LF JPEG and always go back to a copy of the original to reprocess, you should never come up against this problem. It's when you start with a low-resolution file to begin with, or continually re-edit and save any JPEG that compression rears its ugly head. Every time you save a JPEG, you stomp on it just a bit more.

Here's a tip: When editing your files, keep a log of the changes you make (actually write down the numbers when you move the brightness, contrast, shadows etc etc sliders). That makes it much easier to re-process the files when you need to go back and tweak ONE thing...like cropping or sharpness and you want everything else to be the same as on the last version.
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Old 06-26-2009, 07:31 PM   #8
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Nick....any time you see a topic of mine, please become bored. You are a great teacher. I am looking up controlling the input quality of my iPhoto. Thanks.

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Old 06-26-2009, 08:50 PM   #9
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Honestly, there is no way for the screeners to tell the compression ratio of a said photo..... I cannot see the reasoning behind the rejection myself, even on my large monitor.
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Old 06-26-2009, 09:23 PM   #10
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Honestly, there is no way for the screeners to tell the compression ratio of a said photo..... I cannot see the reasoning behind the rejection myself, even on my large monitor.
Just because you can't see it doesn't mean it's not there.

EXIF data in the image in question indicates that the compression level was set at 6 (out of 12). Look at the smooth gray areas and the "Howard" on the left train, as well as the black corrugation lines on the right train... blotchety blotch blotch blotch.
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Old 06-26-2009, 10:42 PM   #11
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Originally Posted by ottergoose View Post
Just because you can't see it doesn't mean it's not there.

EXIF data in the image in question indicates that the compression level was set at 6 (out of 12). Look at the smooth gray areas and the "Howard" on the left train, as well as the black corrugation lines on the right train... blotchety blotch blotch blotch.
This may be true but, the screeners STILL cannot tell the level of compression from the submitted photo. This is one that is not really obvious to the average person. Is this photo RP material? Maybe but, thats not my point here. This is all that I am going to say on this matter.

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Old 06-26-2009, 10:55 PM   #12
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I can look at a photo and see smooth tonal gradients or choppy tonal gradients. This is especially apparent when I view my monitor from extreme angles. If I can see it, the screeners can too.
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Old 06-26-2009, 11:12 PM   #13
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We can see that in plenty of photos excepted to this site tho! Not with the picture in question, on my end atleast.
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Old 06-27-2009, 12:42 AM   #14
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Honestly, there is no way for the screeners to tell the compression ratio of a said photo..... I cannot see the reasoning behind the rejection myself, even on my large monitor.
I don't think the screeners are actually interpreting compression ratios when they use that rejection. Quite simply, if they view the photo and it appears to be over-compressed by saving at a smaller quality (ie: in photoshop, saving a jpg at 5 instead of 12), they select that rejection.
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Old 06-27-2009, 03:41 AM   #15
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Originally Posted by ottergoose View Post
Just because you can't see it doesn't mean it's not there.

EXIF data in the image in question indicates that the compression level was set at 6 (out of 12). Look at the smooth gray areas and the "Howard" on the left train, as well as the black corrugation lines on the right train... blotchety blotch blotch blotch.
Hey Nick...how did you find this EXIF data. And that's the number, the 6 I'm trying to change to 11 or 12, right?

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Old 06-27-2009, 02:20 PM   #16
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Hey Nick...how did you find this EXIF data. And that's the number, the 6 I'm trying to change to 11 or 12, right?

David
When you save in photoshop, do a "save as" and choose the highest quality. On my PS7 you can choose 1-12, 12 being the highest. The exif data is also viewable in photoshop under one of the menu selections. Or, you could simply add an exif viewer to your browser. Just google "exif viewer" and you'll find one right away.
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Old 06-27-2009, 02:33 PM   #17
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In PS CS-3 you have to "Save as" a TIFF then convert it to a JPEG.
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Old 06-27-2009, 03:01 PM   #18
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Hey Nick...how did you find this EXIF data. And that's the number, the 6 I'm trying to change to 11 or 12, right?
If you're running FireFox, which I do, you can install this plugin to see EXIF data:

https://addons.mozilla.org/en-US/firefox/addon/3905

It's probable that other browsers have plugins that do the same thing - as Jim suggested, do a search and see what you can find.
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Old 07-01-2009, 08:14 PM   #19
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It seems that I am limiting myself using the packaged iPhoto that comes with my Mac Lapbook Pro. There is a workshop at the Apple Store here in Chicago and I've signed up. However, iPhoto help desk says there's no such thing as controlling or selecting the import compression (1 -12 has been mentioned) in iPhoto. These compression and quality issues arise when I crop telephoto shots. I need to learn to let the train get closer so that I won't have to crop.

I've also been reading about histograms. A lot of my rejections include "overexposed" but there is little in the photo that looks overexposed to me. On the histogram, however, many times there is a blue spike at the far right. Using crops, the blue turns out to be the sky. Crop out the sky and the overexposure goes away. So the question is, are the screeners looking at the photo or the histogram and if they see the spike, they hit the OE button. Sometimes I can move the spike off the screen to the right...would the screeners still note the OE?

David

Last edited by David Harrison; 07-01-2009 at 08:15 PM. Reason: spelling
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Old 07-01-2009, 09:30 PM   #20
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However, iPhoto help desk says there's no such thing as controlling or selecting the import compression (1 -12 has been mentioned) in iPhoto.
Did you mean export compression? Did you mistakenly ask them about import compression? I'm confused.

Quote:
These compression and quality issues arise when I crop telephoto shots. I need to learn to let the train get closer so that I won't have to crop.
Bingo!

Quote:
So the question is, are the screeners looking at the photo or the histogram and if they see the spike, they hit the OE button.
I don't know but I presume they are looking at the results of the spike, or rather the way the image appears, which is reflected in the spike.
Quote:
Sometimes I can move the spike off the screen to the right...would the screeners still note the OE?
I'm not sure how you would do that, or rather, what that even means. You could increase exposure (or brightness) but that would result in more blown out highlights and a higher spike. Cropping the sky away does result in the spike going away, because the pixels that were represented by the spike no longer exist.
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Old 07-02-2009, 12:11 AM   #21
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Hi JRMDC...I may be misreading what Nick posted in this topic..."There are two causes of excessive JPEG compression
- The image is saved with a high degree of compression (low quality)
- A previously compressed image is reopened and compressed further

To avoid the first cause, make sure you save your images with a high quality setting. I did some googling and it looks like iPhoto will allow you to select a quality setting between 1 and 12 when you save a JPEG. Use 11 or 12 and you'll be all set."

To me it sounded like iPhoto has controls for import. Then Nick said the EXIF data showed my compression to be 6 out of 12. I asked where this data is because the EXIF on this site doesn't list anything to do with compression? Didn't get a response except that there are other sources of EXIF data, besides RP.

Thanks again.

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Old 07-02-2009, 01:11 AM   #22
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To me it sounded like iPhoto has controls for import. Then Nick said the EXIF data showed my compression to be 6 out of 12. I asked where this data is because the EXIF on this site doesn't list anything to do with compression? Didn't get a response except that there are other sources of EXIF data, besides RP.
Export is when you save an image (and set the quality level), import is when you open an image (at that point you're at the mercy of whoever saved it before, you you can't really set a quality level for import). To clarify, you're looking to set the quality of your image when you export it as a JPEG.

To answer your question "where is the EXIF data," the answer is "it's in your photo, but you need some software to see it." If you use FireFox and install the plugin I mentioned, you can right click (or "command" + click on a Mac) on any image on the web and view its EXIF data.

I did some more googling and found this:

http://maccreate.com/iphoto/export-files-from-iphoto

Take a look at that and see where it gets you... I don't see any mention of the 1-12 quality scale there.
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Old 07-02-2009, 01:14 AM   #23
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Hi JRMDC...I may be misreading what Nick posted in this topic..."There are two causes of excessive JPEG compression
- The image is saved with a high degree of compression (low quality)
- A previously compressed image is reopened and compressed further

To avoid the first cause, make sure you save your images with a high quality setting. I did some googling and it looks like iPhoto will allow you to select a quality setting between 1 and 12 when you save a JPEG. Use 11 or 12 and you'll be all set."

To me it sounded like iPhoto has controls for import
Saving a jpg means you get whatever image into iPhoto (raw, jpg, tiff, whatever it accepts, don't know), process it, then when you are done, save it with some level of quality, aka some level of compression. So it is at the end of the process, which I think of as analogous to an export. But it is just saving the work in a particular format.

Quote:
Then Nick said the EXIF data showed my compression to be 6 out of 12. I asked where this data is because the EXIF on this site doesn't list anything to do with compression? Didn't get a response except that there are other sources of EXIF data, besides RP.
That is a full response! The data is stored within the jpg, and software then reads and displays that info. Apparently the RP website software doesn't display everything.
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Old 07-02-2009, 02:25 AM   #24
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Thanks Nick and JR..Here's the process...download from camera to iPhoto, pics are thumbs which can be sized 36 to one per page, but that wouldn't affect the quality, would it? Apple says whatever level was in the camera is imported (10M at FINE-low compression).

Do post processing in iPhoto and click "DONE". When I'm ready to send to RP, click Export (next submission reads full size, length 3258 X height 2422) I click "scale image no larger than..." and enter 1024 and heights changes to 761. Export to Documents. Why don't I export to "Pictures"???? Does it make a difference??? i need to investigate.

In RP they ask "choose file".

Hate to admit it but I just found I have histogram feature in my camera. Plus there's some sort of "arrow matchup" to avoid overexposure. Back to school for me.

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Old 07-02-2009, 04:44 AM   #25
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Thanks Nick and JR..Here's the process...download from camera to iPhoto, pics are thumbs which can be sized 36 to one per page, but that wouldn't affect the quality, would it?
No.

Quote:
click Export (next submission reads full size, length 3258 X height 2422) I click "scale image no larger than..." and enter 1024 and heights changes to 761.
I'd guess it's somewhere in that neighborhood where you get to set the quality of the image that you're exporting.

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Export to Documents. Why don't I export to "Pictures"???? Does it make a difference???
No.
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