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Find Similar Pictures
This search method enables you to find similar or almost identical pictures between the image file formats BMP, JPEG, GIF, PNG and TIF. For each image will be a checksum calculated for further comparison with all other images.The following files will be automatically excluded from the search:
- Files without the extension BMP, JPG, JPEG, GIF, PNG and TIF
- Files with a size of 0 bytes
- Pictures with a width or height smaller than the specified compare size
- Corrupted, invalid or incomplete pictures (*)
- Files with a blocked read access (*)
Comparison Method
The comparison methods aHash, bHash, dHash and pHash enables you to find similar or almost identical pictures by using a percent match lower than 100%. If you want find exactly the same pictures you have to use a percent match of 100% or the comparison methods MD5/SHA.-
aHash
The comparison method aHash (Average Hash) resizes the image to 8x8 or 16x16 pixel. The image will be converted to grayscale and the average color of the all image pixel will be calculated. Now the checksum will be created based on whether the pixel's value is greater than the average color of the image. The checksum can be 64-bit (8x8 pixel) or 256-bit (16x16 pixel). -
bHash
The comparison method bHash (Blockhash) resizes the image to 128x128, 256x256 or 512x512 pixel. The image will be divided into a block matrix and the median value of all blocks will be calculated to create the checksum. The checksum can be 64-bit or 256-bit. The options "Fast" and "Precise" enables you to influence the accuracy of the checksum calculation. -
dHash
The comparison method dHash (Difference Hash) resizes the image to 8x8 or 16x16 pixel. The image will be converted to grayscale and the relative change in brightness intensity between two pixels will be calculated to create the checksum. The checksum can be 64-bit (8x8 pixel) or 256-bit (16x16 pixel). -
pHash
The comparison method pHash (Perceptual Hash) resizes the image to 8x8, 16x16 or 24x24 pixel. The image will be converted to grayscale and the 64-bit checksum will be calculated based on the frequency spectrum data and a distance calculation doing a discrete cosine transform (DCT). -
MD5, SHA
These comparison methods enables you to find exactly the same pictures. The following comparison methods are available:
Percentage Match
Here you can specify the minimum percentage matching of two pictures. The calculated percentage matching between two pictures will be shown at the column Match. The percentage always refers to the reference picture of a group which will be shown in a different text color.Picture Area
This option enables you to specify the picture area to be used to create the checksum. The following options are available:- entire picture
- area at the upper left corner
- area at the upper right corner
- area at the lower left corner
- area at the lower right corner
Compare Size
Here you can specify the maximum width and height of the pictures to be compared. A lower compare size finds more similar pictures and speeds up the comparison time. A higher compare size finds more identical pictures and less similar pictures and of course needs more time to compare them.Checksum
The size of the checksum in bits is shown here.Compare only pictures with the same properties
This option will be performed before the option Detect picture modifications.File Name
This option enables you to compare only pictures with the same file name.File Extension
This option enables you to compare only pictures with the same file extension.Width and Height
This option enables you to compare only pictures with the same width and height.Orientation
This option enables you to compare only pictures with the same orientation (portrait or landscape).Aspect Ratio
This option enables you to compare only pictures with the same aspect ratio. The calculation of the aspect ratio is done by the formula "width divided by height". The result of the calculation is truncated to one decimal place. A picture with 1920x1080 pixel has an aspect ratio of "1.7".
Detect picture modifications (slower)
This option enables you to detect different picture modifications when comparing two pictures. For this purpose, each picture modification will be performed with the picture to be compared and in each case an additional checksum will be created. The following picture modifications can be detected:- Rotated 90° to the right
- Rotated 180° to the right
- Rotated 90° to the left
- Flipped horizontally
- Rotated 90° to the right and flipped horizontally
- Flipped vertically
- Rotated 90° to the left and flipped horizontally
Recognition Rate
We have done several tests with the comparison methods to determine the recognition rate with different image changes. For the test we have created several copies of a JPEG image (2304x3072px, 1.57MB) and changed the color, size or format of the copies. At all tests the original JPEG image and one altered copy of the image have been compared. The following table gives you an overview how good the comparison methods recognize the changes at the image copies. A value of 100% means that the modified image copy will be seen as a full duplicate of the original image.| Modification of the image copy | Compare size |
aHash | dHash | pHash |
|---|---|---|---|---|
| Reduction of the JPG quality to 25% | 8x8 16x16 | 100% 100% | 98% 98% | 97% 100% |
| Reduction of the JPG quality to 50% | 8x8 16x16 | 98% 100% | 98% 98% | 97% 100% |
| Reduction of the JPG quality to 75% | 8x8 16x16 | 100% 100% | 98% 98% | 97% 100% |
| Conversion to grayscale | 8x8 16x16 | 98% 100% | 98% 99% | 97% 100% |
| Conversion to negative | 8x8 16x16 | 2% 0% | 3% 2% | 6% 6% |
| Reduction of the picture size by 50% | 8x8 16x16 | 83% 100% | 75% 97% | 53% 100% |
| Reduction of the picture size by 75% | 8x8 16x16 | 83% 100% | 73% 98% | 53% 100% |
| Enlargement of the picture size by 50% | 8x8 16x16 24x24 | 95% 95% | 92% 85% | 91% 88% 100% |
| Enlargement of the picture size by 100% | 8x8 16x16 24x24 | 94% 91% | 88% 64% | 91% 81% 97% |
| Enlargement of the picture size by 200% | 8x8 16x16 24x24 | 95% 91% | 84% 65% | 88% 78% 88% |
| Reduction of the picture height by 20% | 8x8 16x16 | 95% 100% | 92% 98% | 84% 100% |
| Reduction of the picture width by 20% | 8x8 16x16 | 97% 100% | 86% 98% | 72% 100% |
| Picture rotation by 90° to the left | 8x8 16x16 | 64% 56% | 58% 55% | 56% 53% |
| picture rotation by 90° to the right | 8x8 16x16 24x24 | 56% 56% | 50% 54% | 62% 50% 47% |
| Picture flipped vertically | 8x8 16x16 24x24 | 31% 38% | 59% 58% | 59% 56% 53% |
| Picture flipped horizontally | 8x8 16x16 | 89% 79% | 59% 55% | 56% 50% |
| Removed 100 pixel from the left edge | 8x8 16x16 | 97% 96% | 73% 80% | 75% 91% |
| Removed 100 pixel from the right edge | 8x8 16x16 | 100% 97% | 89% 80% | 97% 91% |
| Removed 100 pixel from the top edge | 8x8 16x16 | 94% 97% | 89% 88% | 84% 97% |
| Removed 100 pixel from the bottom edge | 8x8 16x16 | 100% 96% | 95% 90% | 100% 97% |
| Removed 100 pixel from the left, right, top and bottom edge | 8x8 16x16 | 95% 97% | 73% 79% | 84% 91% |
| Conversion to PNG 24bit | 8x8 16x16 | 100% 100% | 100% 100% | 100% 100% |
| Conversion to PNG 256 colors | 8x8 16x16 | 98% 100% | 98% 98% | 97% 100% |
| Conversion to PNG black/white | 8x8 16x16 | 97% 96% | 81% 70% | 88% 91% |
| Conversion to TIF | 8x8 16x16 | 100% 100% | 100% 100% | 100% 100% |
| Conversion to GIF 256 colors | 8x8 16x16 | 98% 100% | 98% 98% | 97% 100% |
| Conversion to GIF 128 colors | 8x8 16x16 | 100% 99% | 100% 98% | 97% 100% |
| Conversion to GIF 64 colors | 8x8 16x16 | 98% 99% | 97% 98% | 97% 100% |
| Conversion to GIF 32 colors | 8x8 16x16 | 98% 99% | 98% 95% | 97% 100% |
| Conversion to GIF 16 colors | 8x8 16x16 24x24 | 98% 100% | 98% 91% | 97% 97% 100% |
| Conversion to GIF 8 colors | 8x8 16x16 | 98% 100% | 94% 88% | 97% 97% |
| Conversion to GIF 4 colors | 8x8 16x16 | 98% 98% | 89% 84% | 91% 94% |
| Conversion to GIF black/white | 8x8 16x16 | 97% 96% | 81% 70% | 88% 91% |
| Conversion to BMP 24bit | 8x8 16x16 | 100% 100% | 100% 100% | 100% 100% |
| Conversion to BMP 256 colors | 8x8 16x16 | 98% 100% | 98% 98% | 97% 100% |
| Conversion to BMP 16 colors | 8x8 16x16 24x24 | 98% 100% | 98% 91% | 97% 97% 100% |
