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01/02/2003 09:36:07 AM · #1 |
I keep reading your file size is only 76 you know you can go up to 150. What determines the file size. When I get everything ready to submit and resize to the legal dimensions my file size may only be 38. I need some help here. What actually is "file size", how does it help, how do I change from a small file size to a larger size, will it affect the quality of my photo, if so good or bad? This is a serious question. I'm new at doing my own printing.
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01/02/2003 09:54:28 AM · #2 |
i have the oposite problem, i can't get my file size to get down to 150 without significantly reducing its size
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01/02/2003 10:08:55 AM · #3 |
If you got Photoshop use "Save for web" under File.
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01/02/2003 10:11:34 AM · #4 |
PTL, what is the size of your picture when taken from your camera??
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01/02/2003 10:12:17 AM · #5 |
You have to adjust the jpeg quality setting to get your file size down to just under 150 KB. Every time you re-save a JPEG image you lose image quality. Only save your file once. Download the image from your camera, make any color, levels, etc adjustments, add your frame (if desired). Once this is done you want to save your resulting image to your hard drive in an uncompressed or a lossless compressed image format (tiff, bmp, psd, etc). DO NOT SAVE YOUR WORKING IMAGE AS A GIF OR JPEG FILE. Gif images are limited to 256 colors and JPEG images ALWAYS result in lost image quality. Now, once you have your working image saved, resize your image to the size you wish to submit to dpchallenge. You probably want to sharpen your image a little (not too much) after resizing since the resize operation always blurs the image a bit. Now, and only now, are you ready to save the image as a JPEG image. Keep adjusting your JPEG image quality settings in your "Save As" (or "Save for Web" with PhotoShop) properties until the resulting JPEG file size is just under 150 KB.
NOTE: You may get slightly better results by adding your frame after resizing your image instead of before resizing it. This will prevent slight bluring of your frame when the resizing is done.
Shawn
Message edited by author 2003-01-02 10:17:12.
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01/02/2003 10:12:32 AM · #6 |
I mean what is the size like 640 by 480. or is it bigger?
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01/02/2003 10:40:12 AM · #7 |
The jpeq quality setting is the most important thing that determines the file size. Another is: color vs black and white; emptyness vs detail and the other important one is the resolution.
Most imaging programs let you determine the quality level when you save in the jpeg format. They show a box where you can enter a number 1-12 for example or a percentage 0-100%. Others show a slider.
The most common is that the higher the number and the higher the percentage, the higher is the image quality and the lower is the image compression and the bigger is the filesize.
The image size can be explained in two ways. The first is the resolution size: 2048x1536 / 640x480 / 600x600 pixels. That is how big the image will look on the screen. The second is the image file size: 18 megabytes / 150 kilobytes / 76 kilobytes.
The image file size is affected by the compression
The image resolution is determined through resizing, resampling and cropping.
A big resolution contains a lot of data and needs a lot of filesize to be able to show that. The same image at different resolutions has very different filesizes but can have the same quality level, for example:
2048x1536 pixels = 1.5 mb
640x480 = 250kb
400x300 = 100kb
(file sizes are examples only!)
Hard compression (a low file size for a big resolution shows that) causes jpeg artifacts and jpeg compression blocks in the image you are viewing. It takes away the detail, it ruins sharpness and can affect the colors. I have uploaded an example earlier today for someone who asked me to explain what I ment by jpeg artefacts, so check this link to see what happens with file size and image quality in relation to how I set the slider:
//www.pbase.com/azrifel/jpeg_compression
Dpchallenge allows your filesize to be 150kb, that is enough in most cases to ensure that the quality of the file is very good for viewing on a monitor. 76kb is a small filesize for a 640x480 resolution, but big for a 200x300.
(This isn't tutorial quality, but I hope that you see what I mean)
To come back on how the contents of an image can affect the relation between quality and filesize;
Big empty spaces like white paper, a perfectly blue sky, big patches of the same color are very easy to compress without loosing quality. The jpeg algoritm just takes a big area of the same color and for example says that 50x50 pixels of white's (uncompressed that is 2500 parts of information) is one big white square of 50x50 (1 part of information).
It can't do that with details of course. When all pixels in the 50x50 area all have a different color (2500 parts of information) it cannot average that to one color and say that it is a single color square of 50x50. It will try though and that's when you have got to find a balance between the quality setting and filesize.
Do you want all the 2500 different pixels to be visible in the end, you will need a 100% quality and a filesize that can explain 2500 different pixels. On the other end you can get an average color square at 1% quality in a filesize that can explain only 1 pixel and tells the computer to multiply that 2500 times in a 50x50 box.
In reality it isn't as simple as this. It is a very complex algorithm, but this what it basically comes down to.
Message edited by author 2003-01-02 18:49:37.
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01/02/2003 03:41:22 PM · #8 |
Here's another example. The original logo can be found in the top left corner of your browser and this version was saved at the highest PhotoShop 7 compression level (0%).
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01/02/2003 04:14:15 PM · #9 |
Photoshop has a very sophisticated algorithm.
I tried the same with the free Irfanview and the results are much worse (1% quality = 778 bytes). The ribbon is unrecognizable (a gray clutter with a purple square), "a digital photography contest" is unreadable and "dpchallenge" is divided in squares.
Microsoft Photo Editor (1% quality 1226 bytes) looks almost the same as Irfanview. one or two compression block are different.
MGI Photosuite (didn't want to go lower as 25% = 5043 bytes) looks slightly worse than the result of Photoshop 7.
Photoshop 6 produced the same result as 7 at app. the same file size.
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01/02/2003 05:25:01 PM · #10 |
Thank you all for the clear explanation.
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01/02/2003 09:17:41 PM · #11 |
Originally posted by Sonifo:
I mean what is the size like 640 by 480. or is it bigger? |
It's a lot bigger - usually, before cropping any at all, it is over 2000 on one side. Anytime I do any ajustments I save as "a", "b", "b as is sharpened", etc. I always leave the original just as it came from the camera. After I get what I want, saving only one time, I go to the program that re-sizes it to 640 x whatever, always same ratio, and increase dpi from 200 to 300 by 5% increments as stated in the tutorial. When I look at it again it is 78kb, or 38 kb. I don't understand changing the saves from jpeg to something else.
By the way I use MGI PhotoSuite 4 Platnium Edition and re-size with ArcPhoto which came on my HP computer. MGI doesn't have a re-sizer or dpi changer. Maybe this is important in helping me. This is why I've been here so long and haven't submitted.
Checked one out. From the camera it was 2048 x 1536 @ 558kb. Resized it was 402 x 636 @ 44 kb.
Am I just dumb?
Message edited by author 2003-01-02 21:29:51.
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01/02/2003 11:32:54 PM · #12 |
It sounds like you're simply resizing the image and clicking save. When you do that the software is most likely keeping the same level of JPEG compression that was used in the original image from the camera. This is NOT what you want to do. You might try looking under Save As for compression level options. I'm not familiar with the software you're using, so you might have to look around in the various settings for a compression level adjustment (may be called JPEG Quality also).
Shawn
Message edited by author 2003-01-02 23:33:57. |
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