Help for PNGOUTwin

Help Topics

Image Conversion with PNGOUTWin

Use the New File Conversion button or menu to browse to a file and convert it. You can select one or more files to convert.

Use the New Folder Conversion button or menu to convert all of the images of the specified type.

About Image Formats

PNG is a lossless image format: no data is lost when compressing the image. In addition to preserving image fidelity, a PNG image made with PNGOUTWin using a static GIF image as the source will often result in a much smaller file. PNGOUTWin does not support animated GIF conversion.

JPEG is a lossy image file format that sacrifices image fidelity for smaller file size. PNGOUTWin will probably not be able to create a smaller file based on a JPEG source file. If your image flow requires the conversion from JPEG to PNG for a reason other than file size, then PNGOUTWin will be of value to you.

Supported Image Formats

The table below shows the PNG image formats supported by PNGOUTWin.

Indexed color in bit depths 1, 2, 4, 8 with 8 bit transparency Also called PNG8 + 8 bit alpha channel, or palette + alphaYY
Indexed color with 1 bit (GIF) transparency Also called indexed color or paletteYY
Greyscale in bit depths of 1, 2, 4, and 8YY
Greyscale+alpha in bit depths of 1, 2, 4, and 8YY
True Color, also called PNG24YY
True color + alpha, also called PNG24+8 bit alpha channel or PNG32YY

In addition, PNGOUTWin can read many formats, including GIF, TIFF, BMP, and JPG.



The output settings determine where the compressed results created by PNGOUTWin are placed.

Select Put output files in the folder if all output files should go into a designated folder. Click the Change button to choose the folder.
Select Overwrite original file if the file that results should replace the source file. If the result is larger than the source, then the source file is not overwritten.

Select Put output in the same folder as source to create the output file in the same folder as the source file.

Select Preserve file times to set the file time of the result file to that of the source file.

Select the Create new file only when smaller check box to prevent the creation of files that are larger than the source file.

Performance Settings


Change the priority setting to control the level of multitasking support you need. With the priority set to Background you will be able to do more with your PC while PNGOUTWin compresses images, but it will take longer to compress a file. With the priority set to Foreground, PNGOUTWin will compress files the fastest, but your ability to do other tasks on your PC may be diminished. With the priority set to Smart, the priority is set to Background when the application is minimized; otherwise, it runs as with Foreground priority.

PNGOUT Threads

The PNGOUT threads controls the number of worker threads PNGOUTWin uses to compress images. In order for this setting to take effect, the application must be restarted.

Check the Minimize PNGOUTWin Window to System Tray checkbox if you would like to put the application in the taskbar when it is minimized.

Check the Show PNGOUT options after folder/file operation checkbox to be prompted with an advanced dialog before a file or folder is processed. This dialog allows the file to be processed over multiple trials, which can result in smaller files.

Strategy Settings

The strategy setting determines which algorithm will be used to convert or compress an image in the simple UI. The advanced UI, which can be enabled in the Performance page, ignores this setting.

The strategies are listed by increasing computation time. The slower strategies usually result in smaller files.

Chunk Settings

The PNG image format includes chunk data, which includes required and optional information in addition to the image itself. The chunk settings determine which of the optional chunks will be retained in the output file.

By default, no chunks are retained. Choose All to include all chunk data from the source file, even those chunks not listed in the dialog box. If you want to retain only specific chunks, then uncheck None and check the box for those chunks which should be kept.

If a specific chunk is not listed here and you don't need to keep all of the chunks in the source file, then check the Custom checkbox and enter the four letter name for the chunk. Sample chunk names are tEXt and gAMA

Multiple Trials

The strategies in PGNOUTWin for compressing an image can usually make most PNG images smaller, and the same goes for GIF images that are not animated. It is often possible to improve on a single attempt at compressing an image by running multiple trials with different sets of compression parameters.
The Multiple Trials dialog box allows you to run multiple trials over the same file by choosing multiple options. The cross product of the options--that is, all possible combinations of the selected options--will each be attempted on the selected image file or files.

Before we dive into the specifics of the compression parameters, there are a few general guidelines for some common image types

General tips: GIF images will always use paletted mode by default. Therefore, it is often advantageous to play around with the palette options. Keep in mind that some images that have 16 or fewer colors may compress better by using a bit depth of 8 (as counter-intuitive as it may seem). For images with smooth gradients, you will get the most benefit by playing around with the filter options. Mixed filter is often a good guess, but it isn't always the best.

Color Type

If no color type is set, then the same format as the input file will be used.


For paletted images, None is best. Adaptive (mixed) is often the best for grayscale or true color images, but not always.

If auto is chosen, then the same guidelines for filters and color types will be used.

Palette Order

This setting only applies if the color type is Palette or Gray and there are 256 or fewer colors in the image.


This will keep the palette from the source image file without changing its contents or the order of its entries. Using this may hurt compression slightly, but it may be necessary for certain applications (often on small electronic devices) that need to share a common palette.


This starts with the palette from the input file on the initial pass.


This generates a palette from scratch (by converting to RGB and back).

Block Split Threshold

This value is used by the special compression algorithms used in PNGOUTWin. Different values can save a few bytes, although usually the default value is the best.

PNGOUTWin examines the distribution of each file before compression and makes a guess at the optimal number of blocks. Sometimes it makes a good guess. Sometimes it's not the best. This is when it becomes advantageous to fiddle with the block split threshold. Smaller values give more blocks per file, while bigger values result in fewer blocks. Trying different values often results in some savings. There is no way to predict what values work best for a given file.

As a convenience, you can use a threshold value of 0 to specify that whole file should be compressed as 1 big block.

Initial Huffman Tables

The default behavior is to keep the Huffman table from the source files. Randomize is useful for moving out of a local minima: if a file cannot be made smaller with multiple trials and the default Huffman tables, then selecting this option may compress the file a few more bytes. Use this option in trials after the file has been compressed using trials without this setting.

You can often knock off a few extra bytes by running many trials with randomized initial Huffman tables. This feature causes the compression to follow a different path, which affects the ultimate file size by a few bytes. Randomize should always be the last step of the trial process since it has less impact than most other options.

Using Default will result in consistent output sizes. Some people like consistency. That's the only benefit. (Note: Using 'Optimize' palette may result in inconsistent file sizes as well. This is expected behavior).

Bit Depth

This sets the color bit depth to be used in a trial. Auto will minimize the bit depth based on the number of colors in the image.

KSFlate Strategy

No Compression

This is the fastest strategy, but it will result in the largest files. This is useful for when you simply need a conversion to get an image from one system to another that only accepts PNG.

Huffman only

This is faster than all the other strategies except the No Compression strategy, and this provides the least amount of compression.

Longest Match

This strategy is fast and provides a moderate amount of compression.


This strategy is slow and it provides a high level of compression.


Xtreme! is the slowest strategy and it produces the smallest files of all the strategies.

Reset Defaults

Click this button to set all options to their default values.

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