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Maintaining or Reducing Large Jpg to 8 Bit


Mike Mc

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I download many large jpg images that are Resolution - 96 dpi - Bit Depth - 8. But, as soon as I edit them they become 24 Bit and almost double in size.

How can I save them to the original 8 Bit. I cannot upload a sample as they are over 1,000 KB.

TY in Advance

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I am concerned about the size. They are 8 bit B&W pages from large ledgers; example 31.63 X 37.90. But they can be cropped and edited to a smaller size. Yet, when saved it becomes 24 bit and actually larger than the original

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Currently I work with images that start at 5000 x 5000 pixels (52.09 x 52.09 inches), at 96 dpi and a bit depth of 32. When I save to a TIFF in Paint.NET, I get a file that is ~ 3 million bytes. When I save the same image as a JPEG with a bit depth of 24 (at 95% compression) it is half that size. When I save it as a PNG with a bit depth of 8 it is about the same file size as the JPEG. If you need to have a small JPEG file size you will have to increase the compression to ~ 50%. When I save the same file as a 50% compression JPEG, I got the file size down to ~ 0.5 million bytes.

Is there some reason that the bit depth must be 8? If you need a bit depth of 8; you may want to save the file as a GIF.

(The Paint.NET JPEG compression is defaulted at 95%). Remember to set it back if you are going to do other projects during the same session. I will often just close out one session and start a new project in PDN rather than restarting.

Also, JPEG file compression is a lossy file format! Each time a JPEG is open re-worked and saved again, you run the risk of losing image data to each iteration.

As I attempt to live up to the name of "HyReZ", I shoot all of my photos as RAW and convert copies to various file formats depending upon the project or purpose.

 

Edited by HyReZ
Correcting spelling and adding more nfo!


 

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I found that it can be done in GIMP. But, GIMP has an very confusing interface and you cannot change default format of any image. Must be saved in GIMP format OR EXPORTED as jpg.

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Greetings Mike Mc,
 

I had forgotten about the best freeware image file conversion software around.
IranView by Irfan Skiljan, can convert to an 8 bit color depth gray-scale JPEG
When you save as a JPEG make sure that the gray-scale box is checked. That's it!
 

https://www.irfanview.com/

You can also save in batch mode and do all of your image files in one operation!

Edited by HyReZ
inserting additional information
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